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/F0 12/Times-Bold@0 SF(Pr)206.742 192 Q(ogramming in C \255 A T)-.216 E
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G(ernighan)-2.75 E/F2 10/Times-Italic@0 SF(Bell Labor)214.245 240 Q
(atories, Murr)-.15 E(ay Hill, N. J)-.15 E(.)-.25 E/F3 10/Times-Bold@0
SF 2.5(1. Intr)72 319.2 R(oduction)-.18 E F1 3.174(Ci)97 334.8 S 3.174
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(ilable on the).25 F/F4 8/Times-Roman@0 SF(GCOS)3.174 E F1(and)3.174 E
F4(UNIX)3.174 E F1 .673(operating systems at Murray Hill and \(in)3.174
F .633(preliminary form\) on OS/360 at Holmdel.)72 346.8 R 3.133(Cl)
5.633 G .634
(ets you write your programs clearly and simply \255 it has de-)-3.133 F
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(acilities so your code can be read straight do)-3.351 F .751
(wn the page, without labels or GO)-.25 F -.18(TO)-.4 G -.55('s).18 G
3.251(;i).55 G(t)-3.251 E .579(lets you write code that is compact with\
out being too cryptic; it encourages modularity and good program)72
370.8 R(or)72 382.8 Q -.05(ga)-.18 G(nization; and it pro).05 E
(vides good data-structuring f)-.15 E(acilities.)-.1 E .1
(This memorandum is a tutorial to mak)97 398.4 R 2.599(el)-.1 G .099
(earning C as painless as possible.)-2.599 F .099
(The \214rst part concentrates)5.099 F .271(on the central features of \
C; the second part discusses those parts of the language which are usef\
ul \(usually)72 410.4 R .251(for getting more ef)72 422.4 R .251
(\214cient and smaller code\) b)-.25 F .251
(ut which are not necessary for the ne)-.2 F 2.751(wu)-.25 G(ser)-2.751
E 5.251(.T)-.55 G .251(his is)-5.251 F F2(not)2.751 E F1 2.751(ar)2.751
G(ef-)-2.751 E .57(erence manual.)72 434.4 R .57
(Details and special cases will be skipped ruthlessly)5.57 F 3.07(,a)
-.65 G .57(nd no attempt will be made to co)-3.07 F -.15(ve)-.15 G(r).15
E -2.15 -.25(ev e)72 446.4 T .735(ry language feature.).25 F .734
(The order of presentation is hopefully pedagogical instead of logical.)
5.735 F .734(Users who)5.734 F -.1(wo)72 458.4 S .078(uld lik).1 F 2.579
(et)-.1 G .079(he full story should consult the)-2.579 F F2 2.579(CR)
2.579 G(efer)-2.579 E .079(ence Manual)-.37 F F1 .079
(by D. M. Ritchie [1], which should be read)2.579 F .305(for details an)
72 470.4 R(yw)-.15 E(ay)-.1 E 5.305(.R)-.65 G .305
(untime support is described in [2] and [3]; you will ha)-5.305 F .605
-.15(ve t)-.2 H 2.805(or).15 G .305(ead one of these to learn)-2.805 F
(ho)72 482.4 Q 2.5(wt)-.25 G 2.5(oc)-2.5 G(ompile and run a C program.)
-2.5 E 2.024 -.8(We w)97 498 T .424(ill assume that you are f).8 F .424
(amiliar with the mysteries of creating \214les, te)-.1 F .425
(xt editing, and the lik)-.15 F 2.925(ei)-.1 G(n)-2.925 E
(the operating system you run on, and that you ha)72 510 Q .3 -.15(ve p)
-.2 H(rogrammed in some language before.).15 E F3 2.5(2. A)72 534 R
(Simple C Pr)2.5 E(ogram)-.18 E/F5 10/Courier@0 SF 1.5(main\( \) {)108
554.6 R 1.5(printf\("hello, world"\);)144 566.6 R(})108 578.6 Q F1 2.719
(ACp)97 599.2 S .218(rogram consists of one or more)-2.719 F F2
(functions,)2.718 E F1 .218
(which are similar to the functions and subroutines of)2.718 F 3.254(aF)
72 611.2 S .754
(ortran program or the procedures of PL/I, and perhaps some e)-3.404 F
.754(xternal data de\214nitions.)-.15 F F5(main)5.754 E F1 .755
(is such a)3.254 F .061(function, and in f)72 623.2 R .061
(act all C programs must ha)-.1 F .361 -.15(ve a)-.2 H F5(main)2.711 E
/F6 16/Courier@0 SF(.)A F1(Ex)5.06 E .06(ecution of the program be)-.15
F .06(gins at the \214rst state-)-.15 F .252(ment of)72 635.2 R F5(main)
2.752 E F6(.)A F5(main)5.252 E F1 .252(will usually in)2.752 F -.2(vo)
-.4 G .452 -.1(ke o).2 H .253
(ther functions to perform its job, some coming from the same).1 F
(program, and others from libraries.)72 647.2 Q .717
(One method of communicating data between functions is by ar)97 662.8 R
3.216(guments. The)-.18 F .716(parentheses follo)3.216 F(wing)-.25 E .92
(the function name surround the ar)72 674.8 R .92(gument list; here)-.18
F F5(main)3.42 E F1 .92(is a function of no ar)3.42 F .92
(guments, indicated by \()-.18 F(\).)2.5 E .889
(The {} enclose the statements of the function.)72 686.8 R(Indi)5.889 E
.889(vidual statements end with a semicolon b)-.25 F .888(ut are other)
-.2 F(-)-.2 E(wise free-format.)72 698.8 Q F5(printf)97 714.4 Q F1 .551
(is a library function which will format and print output on the termin\
al \(unless some other)3.05 F(destination is speci\214ed\).)72 726.4 Q
(In this)5 E(case it prints)5 E EP
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.208(unction is in)-2.708 F -.2(vo)-.4 G -.1(ke).2 G 2.708(db).1 G 2.708
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F .208(guments in parentheses.)-.18 F .208(There is no)5.208 F/F2 8
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-.75(Wo)2.5 G(rking C Pr).75 E(ogram; V)-.18 E(ariables; T)-.92 E
(ypes and T)-.74 E(ype Declarations)-.74 E F0(Here')97 157.6 Q 2.5(sab)
-.55 G(igger program that adds three inte)-2.5 E
(gers and prints their sum.)-.15 E F1 1.5(main\( \) {)108 174.6 R 1.5
(int a, b, c, sum;)144 186.6 R 7.5(a=1)144 198.6 S 15(;b)-7.5 G 7.5(=2)
-7.5 G 15(;c)-7.5 G 7.5(=3)-7.5 G(;)-7.5 E 1.5(sum = a + b + c;)144
210.6 R 1.5(printf\("sum is %d", sum\);)144 222.6 R(})108 234.6 Q F0
1.621
(Arithmetic and the assignment statements are much the same as in F)97
255.2 R 1.621(ortran \(e)-.15 F 1.621(xcept for the semi-)-.15 F .09
(colons\) or)72 267.2 R F2(PL/I.)2.59 E F0 .09
(The format of C programs is quite free.)5.09 F 1.69 -.8(We c)5.09 H .09
(an put se).8 F -.15(ve)-.25 G .089(ral statements on a line if we w).15
F(ant,)-.1 E .589(or we can split a statement among se)72 279.2 R -.15
(ve)-.25 G .59
(ral lines if it seems desirable. The split may be between an).15 F 3.09
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303.2 Q(wlines should be used freely to enhance readability)-.25 E(.)
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(of v)2.5 E(ariables:)-.25 E F1(int)108 336.8 Q F0(inte)18 E
(ger \(PDP-11: 16 bits; H6070: 36 bits; IBM360: 32 bits\))-.15 E F1
(char)108 348.8 Q F0
(one byte character \(PDP-11, IBM360: 8 bits; H6070: 9 bits\))12 E F1
(float)108 360.8 Q F0(single-precision \215oating point)6 E F1(double)
108 372.8 Q F0(double-precision \215oating point)36 E .696
(There are also)72 390.8 R F4(arr)3.196 E(ays)-.15 E F0(and)3.196 E F4
(structur)3.196 E(es)-.37 E F0 .696(of these basic types,)3.196 F F4
(pointer)3.197 E(s)-.1 E F0 .697(to them and)3.197 F F4(functions)3.197
E F0 .697(that return them,)3.197 F(all of which we will meet shortly)72
402.8 Q(.)-.65 E F4(All)97 418.4 Q F0 -.25(va)3.598 G 1.097(riables in \
a C program must be declared, although this can sometimes be done impli\
citly by).25 F(conte)72 430.4 Q 2.5(xt. Declarations)-.15 F
(must precede e)2.5 E -.15(xe)-.15 G(cutable statements.).15 E
(The declaration)5 E F1 1.5(int a, b, c, sum;)108 447.4 R F0(declares)72
464.4 Q F1 -3.5(a, b, c,)2.5 F F0(and)2.5 E F1(sum)2.5 E F0(to be inte)
2.5 E(gers.)-.15 E -1.11(Va)97 480 S .46(riable names ha)1.11 F .76 -.15
(ve o)-.2 H .4 LW 414.485 482.5 409.485 482.5 DL .46
(ne to eight characters, chosen from A-Z, a-z, 0-9, and)188.28 480 R
2.961(,a)7.961 G .461(nd start with a non-)-2.961 F 4.159
(digit. Stylistically)72 492 R 4.159(,i)-.65 G(t')-4.159 E 4.159(sm)-.55
G 1.659(uch better to use only a single case and gi)-4.159 F 1.958 -.15
(ve f)-.25 H 1.658(unctions and e).15 F 1.658(xternal v)-.15 F(ariables)
-.25 E .243(names that are unique in the \214rst six characters.)72 504
R .243(\(Function and e)5.243 F .243(xternal v)-.15 F .243
(ariable names are used by v)-.25 F(arious)-.25 E 1.077(assemblers, som\
e of which are limited in the size and case of identi\214ers the)72 516
R 3.577(yc)-.15 G 1.076(an handle.\))-3.577 F(Furthermore,)6.076 E -.1
(ke)72 528 S(yw)-.05 E
(ords and library functions may only be recognized in one case.)-.1 E F3
2.5(4. Constants)72 552 R F0 1.842 -.8(We h)97 567.6 T -2.25 -.2(av e).8
H .242(already seen decimal inte)2.942 F .242(ger constants in the pre)
-.15 F .243(vious e)-.25 F .243(xample _ 1, 2, and 3.)-.15 F .243
(Since C is of-)5.243 F 1.359(ten used for system programming and bit-m\
anipulation, octal numbers are an important part of the lan-)72 579.6 R
2.799(guage. In)72 591.6 R .299(C, an)2.799 F 2.799(yn)-.15 G .299
(umber that be)-2.799 F .299(gins with 0 \(zero!\))-.15 F .299
(is an octal inte)5.299 F .299(ger \(and hence can')-.15 F 2.799(th)-.18
G -2.25 -.2(av e)-2.799 H(an)2.999 E 2.799(y8)-.15 G 1.399 -.55('s o)
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(Thus 0777 is an octal constant, with decimal v)5 E(alue 511.)-.25 E
3.108(A`)97 619.2 S(`character')-3.848 E 3.108('i)-.74 G 3.108(so)-3.108
G .608(ne byte \(an inherently machine-dependent concept\).)-3.108 F
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F4 -.15(ch)2.759 G(ar).15 E .259(acter constant,)-.15 F F0 .259
(which is one character enclosed in single quotes.)2.759 F(Ho)5.26 E(we)
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643.2 Q F1(flags)2.5 E F0(belo)2.5 E(w:)-.25 E F1 1.5
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/F0 10/Times-Roman@0 SF 2.5(CT)72 36 S 182.23(utorial -)-2.95 F 2.5(3-)
2.5 G .625(The sequence `\\n' is C notation for `)97 87.6 R(`ne)-.74 E
.625(wline character')-.25 F .624
(', which, when printed, skips the terminal to)-.74 F .704(the be)72
99.6 R .704(ginning of the ne)-.15 F .704(xt line.)-.15 F .704
(Notice that `\\n' represents only a single character)5.704 F 5.704(.T)
-.55 G .704(here are se)-5.704 F -.15(ve)-.25 G .705(ral other).15 F
-.74(``)72 111.6 S(escapes').74 E 5.033('l)-.74 G(ik)-5.033 E 5.033(e`)
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F 2.532(visible characters, such as `\\t' for tab, `\\b' for)-.4 F(back\
space, `\\0' for end of \214le, and `\\\\' for the backslash itself.)72
123.6 Q/F1 10/Courier@0 SF(float)97 139.2 Q F0(and)2.5 E F1(double)2.5 E
F0(constants are discussed in section 26.)2.5 E/F2 10/Times-Bold@0 SF
2.5(5. Simple)72 163.2 R(I/O _ getchar)2.5 E 2.5(,p)-.92 G(utchar)-2.5 E
2.5(,p)-.92 G(rintf)-2.5 E F1 1.5(main\( \) {)108 183.8 R 1.5(char c;)
144 195.8 R 7.5(c=g)144 207.8 S 1.5(etchar\( \);)-7.5 F(putchar\(c\);)
144 219.8 Q(})108 231.8 Q(getchar)97 252.4 Q F0(and)3.251 E F1(putchar)
3.251 E F0 .751(are the basic I/O library functions in C.)3.251 F F1
(getchar)5.752 E F0 .752(fetches one character)3.252 F .516(from the st\
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ns that character as the v)72 264.4 R(alue)-.25 E .045(of the function.)
72 276.4 R .045(When it reaches the end of whate)5.045 F -.15(ve)-.25 G
2.545<728c>.15 G .046
(le it is reading, thereafter it returns the character rep-)-2.545 F
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(So the program abo)72 316 R .985 -.15(ve r)-.15 H .685
(eads one character and writes it back out.).15 F .686
(By itself, this isn')5.686 F 3.186(tv)-.18 G .686(ery interesting, b)
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(ying one \214le to another)-.1 E(.)-.55 E F1(printf)97 355.6 Q F0 .141
(is a more complicated function for producing formatted output.)2.641 F
1.742 -.8(We w)5.141 H .142(ill talk about only the).8 F .216
(simplest use of it.)72 367.6 R(Basically)5.216 E(,)-.65 E F1(printf)
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(gument as formatting information, and an)-.18 F 2.716(ys)-.15 G
(uccessi)-2.716 E -.15(ve)-.25 G(ar)72 379.6 Q(guments as v)-.18 E
(ariables to be output.)-.25 E(Thus)5 E F1 1.5
(printf \("hello, world\\n"\);)108 396.6 R F0 .259
(is the simplest use _ the string `)72 413.6 R .259(`hello, w)-.74 F
(orld\\n')-.1 E 2.759('i)-.74 G 2.759(sp)-2.759 G .26(rinted out.)-2.759
F .26(No formatting information, no v)5.26 F .26(ariables, so)-.25 F
.678(the string is dumped out v)72 425.6 R 3.178(erbatim. The)-.15 F(ne)
3.178 E .677(wline is necessary to put this out on a line by itself.)
-.25 F .677(\(The con-)5.677 F(struction)72 437.6 Q F1 1.5
("hello, world\\n")108 454.6 R F0(is really an array of)72 471.6 Q F1
(chars)2.5 E/F4 16/Courier@0 SF(.)A F0(More about this shortly)5 E(.\))
-.65 E(More complicated, if)97 487.2 Q F1(sum)2.5 E F0(is 6,)2.5 E F1
1.5(printf \("sum is %d\\n", sum\);)108 504.2 R F0(prints)72 521.2 Q F1
1.5(sum is 6)108 538.2 R F0 -.4(Wi)72 555.2 S .234(thin the \214rst ar)
.4 F .234(gument of)-.18 F F1(printf,)2.734 E F0 .234(the characters `)
2.734 F(`%d')-.74 E 2.734('s)-.74 G .235(ignify that the ne)-2.734 F
.235(xt ar)-.15 F .235(gument in the ar)-.18 F(gument)-.18 E
(list is to be printed as a base 10 number)72 567.2 Q(.)-.55 E .158
(Other useful formatting commands are `)97 582.8 R(`%c')-.74 E 2.658('t)
-.74 G 2.658(op)-2.658 G .158(rint out a single character)-2.658 F 2.657
(,`)-.4 G(`%s')-3.397 E 2.657('t)-.74 G 2.657(op)-2.657 G .157
(rint out an en-)-2.657 F(tire string, and `)72 594.8 Q(`%o')-.74 E 2.5
('t)-.74 G 2.5(op)-2.5 G
(rint a number as octal instead of decimal \(no leading zero\).)-2.5 E
-.15(Fo)5 G 2.5(re).15 G(xample,)-2.65 E F1 7.5(n=5)108 611.8 S(11;)-7.5
E 1.5(printf \("What is the value of %d in octal?", n\);)108 623.8 R 1.5
(printf \(")108 635.8 R 1.5
(%s! %d decimal is %o octal\\n", "Right", n, n\);)15 F F0(prints)72
652.8 Q F1 2.375(What is the value of 511 in octal?)108 669.8 R 2.375
(Right! 511 decimal is 777)15.875 F(octal)108 681.8 Q F0 1.514
(Notice that there is no ne)72 698.8 R 1.514
(wline at the end of the \214rst output line.)-.25 F(Successi)6.514 E
1.814 -.15(ve c)-.25 H 1.514(alls to).15 F F1(printf)4.013 E F0
(\(and/or)4.013 E F1(putchar,)72 710.8 Q F0 .912
(for that matter\) simply put out characters.)3.411 F .912(No ne)5.912 F
.912(wlines are printed unless you ask for them.)-.25 F(Similarly)72
722.8 Q 2.688(,o)-.65 G 2.688(ni)-2.688 G .188
(nput, characters are read one at a time as you ask for them.)-2.688 F
.188(Each line is generally terminated)5.188 F EP
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/F0 10/Times-Roman@0 SF 2.5(CT)72 36 S 182.23(utorial -)-2.95 F 2.5(4-)
2.5 G(by a ne)72 84 Q(wline \(\\n\), b)-.25 E
(ut there is otherwise no concept of record.)-.2 E/F1 10/Times-Bold@0 SF
2.5(6. If;)72 108 R -.18(re)2.5 G
(lational operators; compound statements).18 E F0
(The basic conditional-testing statement in C is the)97 123.6 Q/F2 10
/Courier@0 SF(if)2.5 E F0(statement:)2.5 E F2 7.5(c=g)108 140.6 S 1.5
(etchar\( \);)-7.5 F 1.5(if\( c)108 152.6 R F0(==)7.5 E/F3 10/Symbol SF
<a2>7.5 E F2(?)A F3<a2>A F2(\))7.5 E 1.5
(printf\("why did you type a question mark?\\n"\);)144 164.6 R F0
(The simplest form of)72 181.6 Q F2(if)2.5 E F0(is)2.5 E F2 1.5
(if \(expression\) statement)108 198.6 R F0 .735
(The condition to be tested is an)97 219.2 R 3.236(ye)-.15 G .736
(xpression enclosed in parentheses.)-3.386 F .736(It is follo)5.736 F
.736(wed by a statement.)-.25 F 1.316(The e)72 231.2 R 1.316
(xpression is e)-.15 F -.25(va)-.25 G 1.316(luated, and if its v).25 F
1.316(alue is non-zero, the statement is e)-.25 F -.15(xe)-.15 G 3.815
(cuted. There').15 F 3.815(sa)-.55 G 3.815(no)-3.815 G(ptional)-3.815 E
F2(else)72 243.2 Q F0(clause, to be described soon.)2.5 E
(The character sequence `==')97 258.8 Q
(is one of the relational operators in C; here is the complete set:)5 E
(==)108 275.8 Q F2 1.5(equal to \()24.72 F/F4 16/Courier@0 SF(.)A F2(EQ)
A F4(.)A F2 1.5(to Fortraners\))7.5 F 18(!= not)108 287.8 R 1.5
(equal to)7.5 F 30(>g)108 299.8 S 1.5(reater than)-30 F 30(<l)108 311.8
S 1.5(ess than)-30 F 18(>= greater)108 323.8 R 1.5(than or equal to)7.5
F 18(<= less)108 335.8 R 1.5(than or equal to)7.5 F F0 1.426(The v)97
356.4 R 1.426(alue of)-.25 F F2 -2.074
(``expression relation expression'')3.926 F F0 1.426
(is 1 if the relation is true, and 0 if)3.926 F -.1(fa)72 368.4 S 2.581
(lse. Don').1 F 2.581(tf)-.18 G(or)-2.581 E .08(get that the equality t\
est is `=='; a single `=' causes an assignment, not a test, and in)-.18
F -.25(va)-.4 G(riably).25 E(leads to disaster)72 380.4 Q(.)-.55 E -.7
(Te)97 396 S .583(sts can be combined with the operators).7 F F2(`&&')
3.084 E/F5 8/Times-Roman@0 SF(\(AND\),)3.084 E .4 LW 330.788 389.25
330.788 396 DL 334.454 389.25 334.454 396 DL F2 5.666(`')323.788 396 S
F5(\(OR\),)-2.582 E F0(and)3.084 E F2(`!')3.084 E F5(\(NO)5.584 E(T\).)
-.32 E F0 -.15(Fo)5.584 G 3.084(re).15 G .584(xample, we)-3.234 F
(can test whether a character is blank or tab or ne)72 408 Q(wline with)
-.25 E F2 1.5(if\( c)108 425 R F0(==)A 171.72 418.25 171.72 425 DL
175.386 418.25 175.386 425 DL F3 7.5<a2a2>150.78 425 S F2(c)13.166 E F0
(==)A F3<a2>A F2(\\t)A 226.606 418.25 226.606 425 DL 230.272 418.25
230.272 425 DL F3<a2>215.636 425 Q F2(c)20.666 E F0(==)A F3<a2>A F2(\\n)
A F3<a2>A F2(\))7.5 E F4(...)7.5 E F0 2.5(Cg)72 442 S(uarantees that)
-2.5 E F2(`&&')2.5 E F0(and)2.5 E 194.37 435.25 194.37 442 DL 198.036
435.25 198.036 442 DL F2 5.666(`')187.37 442 S F0(are e)-3.166 E -.25
(va)-.25 G
(luated left to right _ we shall soon see cases where this matters.).25
E .158(One of the nice things about C is that the)97 457.6 R F2
(statement)2.658 E F0 .158(part of an)2.658 F F2(if)2.658 E F0 .158
(can be made arbitrarily compli-)2.658 F .107
(cated by enclosing a set of statements in {}.)72 469.6 R .108
(As a simple e)5.108 F .108(xample, suppose we w)-.15 F .108
(ant to ensure that)-.1 F F2(a)2.608 E F0 .108(is big-)2.608 F .575
(ger than)72 481.6 R F2(b,)3.075 E F0 .575(as part of a sort routine.)
3.075 F .575(The interchange of)5.575 F F2(a)3.075 E F0(and)3.075 E F2
(b)3.075 E F0(tak)3.075 E .574(es three statements in C, grouped to-)-.1
F(gether by {}:)72 493.6 Q F2 1.5(if \(a < b\) {)108 510.6 R 7.5(t=a)144
522.6 S(;)-7.5 E 7.5(a=b)144 534.6 S(;)-7.5 E 7.5(b=t)144 546.6 S(;)-7.5
E(})108 558.6 Q F0 .626(As a general rule in C, an)97 579.2 R .626
(ywhere you can use a simple statement, you can use an)-.15 F 3.127(yc)
-.15 G .627(ompound state-)-3.127 F .063(ment, which is just a number o\
f simple or compound ones enclosed in {}.)72 591.2 R .063
(There is no semicolon after the })5.063 F(of a compound statement, b)72
603.2 Q(ut there)-.2 E/F6 10/Times-Italic@0 SF(is)2.5 E F0 2.5(as)2.5 G
(emicolon after the last non-compound statement inside the {}.)-2.5 E
1.001(The ability to replace single statements by comple)97 618.8 R
3.501(xo)-.15 G 1.001(nes at will is one feature that mak)-3.501 F 1.002
(es C much)-.1 F .36(more pleasant to use than F)72 630.8 R 2.86
(ortran. Logic)-.15 F(\(lik)2.86 E 2.86(et)-.1 G .36(he e)-2.86 F .36
(xchange in the pre)-.15 F .36(vious e)-.25 F .36(xample\) which w)-.15
F .36(ould require)-.1 F(se)72 642.8 Q -.15(ve)-.25 G 1.312(ral GO).15 F
-.18(TO)-.4 G 2.412 -.55('s a).18 H 1.312(nd labels in F).55 F 1.312
(ortran can and should be done in C without an)-.15 F 2.613 -.65(y, u)
-.15 H 1.313(sing compound state-).65 F(ments.)72 654.8 Q F1 2.5
(7. While)72 678.8 R(Statement; Assignment within an Expr)2.5 E
(ession; Null Statement)-.18 E F0 .169
(The basic looping mechanism in C is the)97 694.4 R F2(while)2.668 E F0
2.668(statement. Here')2.668 F 2.668(sap)-.55 G .168
(rogram that copies its input to)-2.668 F
(its output a character at a time.)72 706.4 Q
(Remember that `\\0' marks the end of \214le.)5 E F2 1.5(main\( \) {)108
723.4 R EP
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/F0 10/Courier@0 SF 7.5(CT)72 36 S(utorial)-7.5 E/F1 10/Symbol SF(-)
156.51 E F0(5)7.5 E F1(-)7.5 E F0 1.5(char c;)144 84 R 1.5
(while\( \(c=getchar\( \)\) !=)144 96 R F1<a2>7.5 E F0(\\0)A F1<a2>A F0
(\))7.5 E(putchar\(c\);)180 108 Q(})108 120 Q/F2 10/Times-Roman@0 SF
(The)72 137 Q F0(while)2.5 E F2
(statement is a loop, whose general form is)2.5 E F0 1.5
(while \(expression\) statement)108 154 R F2(Its meaning is)72 171 Q F0
1.5(\(a\) evaluate the expression)108 188 R 1.5
(\(b\) if its value is true \(i)108 200 R/F3 16/Courier@0 SF(.)A F0(e)A
F3(.)A F0 7.5(,n)C 1.5(ot zero\))-7.5 F 1.5
(do the statement, and go back to \(a\))180 212 R F2 .716(Because the e)
72 229 R .717(xpression is tested before the statement is e)-.15 F -.15
(xe)-.15 G .717(cuted, the statement part can be e).15 F -.15(xe)-.15 G
.717(cuted zero).15 F .352(times, which is often desirable.)72 241 R
.351(As in the)5.351 F F0(if)2.851 E F2 .351(statement, the e)2.851 F
.351(xpression and the statement can both be arbi-)-.15 F .15
(trarily complicated, although we ha)72 253 R -.15(ve)-.2 G(n').15 E
2.65(ts)-.18 G .15(een that yet.)-2.65 F .15(Our e)5.15 F .15
(xample gets the character)-.15 F 2.65(,a)-.4 G .15(ssigns it to)-2.65 F
F0(c,)2.65 E F2(and)2.65 E .028(then tests if it')72 265 R 2.528(sa`)
-.55 G(\\0')-2.528 E 2.528('. If)-.74 F .027
(it is not a `\\0', the statement part of the)2.527 F F0(while)2.527 E
F2 .027(is e)2.527 F -.15(xe)-.15 G .027(cuted, printing the character)
.15 F(.)-.55 E(The)72 277 Q F0(while)3.585 E F2 1.086(then repeats.)
3.585 F 1.086(When the input character is \214nally a `\\0', the)6.086 F
F0(while)3.586 E F2 1.086(terminates, and so does)3.586 F F0(main)72 289
Q F3(.)A F2(Notice that we used an assignment statement)97 304.6 Q F0
7.5(c=g)108 321.6 S 1.5(etchar\( \))-7.5 F F2 .611(within an e)72 338.6
R 3.111(xpression. This)-.15 F .611
(is a handy notational shortcut which often produces clearer code.)3.111
F .61(\(In f)5.61 F .61(act it is)-.1 F .133(often the only w)72 350.6 R
.133(ay to write the code cleanly)-.1 F 5.133(.A)-.65 G 2.633(sa)-5.133
G 2.633(ne)-2.633 G -.15(xe)-2.783 G .134
(rcise, re-write the \214le-cop).15 F 2.634(yw)-.1 G .134
(ithout using an assign-)-2.634 F .105(ment inside an e)72 362.6 R 2.604
(xpression.\) It)-.15 F -.1(wo)2.604 G .104
(rks because an assignment statement has a v).1 F .104(alue, just as an)
-.25 F 2.604(yo)-.15 G .104(ther e)-2.604 F(xpres-)-.15 E .571
(sion does.)72 374.6 R .571(Its v)5.571 F .571(alue is the v)-.25 F .571
(alue of the right hand side.)-.25 F .571
(This also implies that we can use multiple assign-)5.571 F(ments lik)72
386.6 Q(e)-.1 E F0 7.5(x=y=z=0)108 403.6 S(;)-7.5 E F2(Ev)72 420.6 Q
(aluation goes from right to left.)-.25 E .198(By the w)97 436.2 R(ay)
-.1 E 2.698(,t)-.65 G .198(he e)-2.698 F .198(xtra parentheses in the a\
ssignment statement within the conditional were really nec-)-.15 F
(essary: if we had said)72 448.2 Q F0 7.5(c=g)108 465.2 S 1.5
(etchar\( \) !=)-7.5 F F1<a2>7.5 E F0(\\0)A F1<a2>A F0(c)72 482.2 Q F2
-.1(wo)2.978 G .479
(uld be set to 0 or 1 depending on whether the character fetched w).1 F
.479(as an end of \214le or not.)-.1 F .479(This is be-)5.479 F 1.113
(cause in the absence of parentheses the assignment operator `=' is e)72
494.2 R -.25(va)-.25 G 1.113(luated after the relational operator).25 F
2.5(`!='. When)72 506.2 R(in doubt, or e)2.5 E -.15(ve)-.25 G 2.5(ni).15
G 2.5(fn)-2.5 G(ot, parenthesize.)-2.5 E(Since)97 521.8 Q F0
(putchar\(c\))3.43 E F2(returns)3.43 E F0(c)3.43 E F2 .93
(as its function v)3.43 F .931(alue, we could also cop)-.25 F 3.431(yt)
-.1 G .931(he input to the output by)-3.431 F(nesting the calls to)72
533.8 Q F0(getchar)2.5 E F2(and)2.5 E F0(putchar:)2.5 E 1.5(main\( \) {)
108 550.8 R 1.5(while\( putchar\(getchar\( \)\) !=)144 562.8 R F1<a2>7.5
E F0(\\0)A F1<a2>A F0 7.5(\);)7.5 G(})108 574.8 Q F2 .733
(What statement is being repeated?)72 591.8 R .733(None, or technically)
5.733 F 3.233(,t)-.65 G(he)-3.233 E/F4 10/Times-Italic@0 SF(null)3.232 E
F2 .732(statement, because all the w)3.232 F .732(ork is really)-.1 F
.46(done within the test part of the)72 603.8 R F0(while)2.96 E F3(.)A
F2 .46(This v)5.46 F .46(ersion is slightly dif)-.15 F .46
(ferent from the pre)-.25 F .46(vious one, because)-.25 F
(the \214nal `\\0' is copied to the output before we decide to stop.)72
615.8 Q/F5 10/Times-Bold@0 SF 2.5(8. Arithmetic)72 639.8 R F2 .172
(The arithmetic operators are the usual `+', `)97 655.4 R F1(-)A F2 .172
(', `*', and `/' \(truncating inte)B .172(ger di)-.15 F .171
(vision if the operands)-.25 F(are both)72 667.4 Q F0(int\),)2.5 E F2
(and the remainder or mod operator `%':)2.5 E F0 7.5(x=a)108 684.4 S
(%b;)-7.5 E F2(sets)72 701.4 Q F0(x)2.686 E F2 .186
(to the remainder after)2.686 F F0(a)2.686 E F2 .186(is di)2.686 F .186
(vided by)-.25 F F0(b)2.686 E F2(\(i.e.,)2.686 E F0 2.686(am)2.686 G
-3.314(od b\))-2.686 F F3(.)A F2 .186
(The results are machine dependent unless)5.186 F EP
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/F0 10/Times-Roman@0 SF 2.5(CT)72 36 S 182.23(utorial -)-2.95 F 2.5(6-)
2.5 G/F1 10/Courier@0 SF(a)72 84 Q F0(and)2.5 E F1(b)2.5 E F0
(are both positi)2.5 E -.15(ve)-.25 G(.).15 E .505(In arithmetic,)97
99.6 R F1(char)3.005 E F0 -.25(va)3.005 G .505
(riables can usually be treated lik).25 F(e)-.1 E F1(int)3.005 E F0 -.25
(va)3.005 G 3.005(riables. Arithmetic).25 F .505(on characters is)3.005
F(quite le)72 111.6 Q -.05(ga)-.15 G(l, and often mak).05 E(es sense:)
-.1 E F1 7.5(c=c+)108 128.6 S/F2 10/Symbol SF<a2>A F1(A)A F2 7.5<a22da2>
C F1(a)-7.5 E F2<a2>A F1(;)A F0(con)72 145.6 Q -.15(ve)-.4 G 1.159
(rts a single lo).15 F 1.159(wer case ascii character stored in)-.25 F
F1(c)3.659 E F0 1.159(to upper case, making use of the f)3.659 F 1.159
(act that corre-)-.1 F .916(sponding ascii letters are a \214x)72 157.6
R .916(ed distance apart.)-.15 F .916(The rule go)5.916 F -.15(ve)-.15 G
.916(rning this arithmetic is that all).15 F F1(chars)3.415 E F0(are)
3.415 E(con)72 169.6 Q -.15(ve)-.4 G .088(rted to).15 F F1(int)2.588 E
F0 .089(before the arithmetic is done.)2.588 F(Be)5.089 E -.1(wa)-.25 G
.089(re that con).1 F -.15(ve)-.4 G .089(rsion may in).15 F -.2(vo)-.4 G
(lv).2 E 2.589(es)-.15 G(ign-e)-2.589 E .089(xtension _ if the)-.15 F
.47(leftmost bit of a character is 1, the resulting inte)72 181.6 R .47
(ger might be ne)-.15 F -.05(ga)-.15 G(ti).05 E -.15(ve)-.25 G 5.47(.\()
.15 G .47(This doesn')-5.47 F 2.97(th)-.18 G .47(appen with genuine)
-2.97 F(characters on an)72 193.6 Q 2.5(yc)-.15 G(urrent machine.\))-2.5
E(So to con)97 209.2 Q -.15(ve)-.4 G(rt a \214le into lo).15 E
(wer case:)-.25 E F1 1.5(main\( \) {)108 226.2 R 1.5(char c;)144 238.2 R
1.5(while\( \(c=getchar\( \)\) !=)144 250.2 R F2<a2>7.5 E F1(\\0)A F2
<a2>A F1(\))7.5 E(if\()180 262.2 Q F2<a2>7.5 E F1(A)A F2<a2>A F1 1.5
(<=c && c<=)B F2<a2>A F1(Z)A F2<a2>A F1(\))7.5 E(putchar\(c+)216 274.2 Q
F2<a2>A F1(a)A F2<a22da2>A F1(A)A F2<a2>A F1(\);)A(else)180 286.2 Q
(putchar\(c\);)216 298.2 Q(})108 310.2 Q F0 .637(Characters ha)72 327.2
R .937 -.15(ve d)-.2 H(if).15 E .637(ferent sizes on dif)-.25 F .637
(ferent machines.)-.25 F(Further)5.637 E 3.137(,t)-.4 G .637(his code w)
-3.137 F(on')-.1 E 3.138(tw)-.18 G .638(ork on an IBM machine,)-3.238 F
(because the letters in the ebcdic alphabet are not contiguous.)72 339.2
Q/F3 10/Times-Bold@0 SF 2.5(9. Else)72 363.2 R(Clause; Conditional Expr)
2.5 E(essions)-.18 E F0 1.6 -.8(We j)97 378.8 T(ust used an).8 E F1
(else)2.5 E F0(after an)2.5 E F1(if)2.5 E/F4 16/Courier@0 SF(.)A F0
(The most general form of)5 E F1(if)2.5 E F0(is)2.5 E F1 1.5
(if \(expression\) statement1 else statement2)108 395.8 R F0(the)72
412.8 Q F1(else)2.5 E F0(part is optional, b)2.5 E(ut often useful.)-.2
E(The canonical e)5 E(xample sets)-.15 E F1(x)2.5 E F0
(to the minimum of)2.5 E F1(a)2.5 E F0(and)2.5 E F1(b:)2.5 E 1.5
(if \(a < b\))108 429.8 R 7.5(x=a)144 441.8 S(;)-7.5 E(else)108 453.8 Q
7.5(x=b)144 465.8 S(;)-7.5 E F0(Observ)72 482.8 Q 2.5(et)-.15 G
(hat there')-2.5 E 2.5(sas)-.55 G(emicolon after)-2.5 E F1(x=a)2.5 E F4
(.)A F0 2.65(Cp)97 498.4 S(ro)-2.65 E .15
(vides an alternate form of conditional which is often more concise.)
-.15 F .15(It is called the `)5.15 F(`conditional)-.74 E -.15(ex)72
510.4 S(pression').15 E 2.822('b)-.74 G .323
(ecause it is a conditional which actually has a v)-2.822 F .323
(alue and can be used an)-.25 F .323(ywhere an e)-.15 F(xpression)-.15 E
2.5(can. The)72 522.4 R -.25(va)2.5 G(lue of).25 E F1 1.5(a<b ? a : b;)
108 539.4 R F0(is)72 556.4 Q F1(a)2.5 E F0(if)2.5 E F1(a)2.5 E F0
(is less than)2.5 E F1(b;)2.5 E F0(it is)2.5 E F1(b)2.5 E F0 2.5
(otherwise. In)2.5 F(general, the form)2.5 E F1 1.5
(expr1 ? expr2 : expr3)108 573.4 R F0 .3(means `)72 590.4 R(`e)-.74 E
-.25(va)-.25 G(luate).25 E F1(expr1)2.8 E F4(.)A F0 .3
(If it is not zero, the v)5.3 F .3(alue of the whole thing is)-.25 F F1
(expr2;)2.8 E F0 .3(otherwise the v)2.8 F .3(alue is)-.25 F F1(expr3)72
602.4 Q F4(.)A F1('')A F0 1.6 -.8(To s)97 618 T(et).8 E F1(x)2.5 E F0
(to the minimum of)2.5 E F1(a)2.5 E F0(and)2.5 E F1(b,)2.5 E F0(then:)
2.5 E F1 7.5(x=\()108 635 S 1.5(a<b ? a : b\);)-7.5 F F0
(The parentheses aren')72 652 Q 2.5(tn)-.18 G(ecessary because)-2.5 E F1
(`?:')2.5 E F0(is e)2.5 E -.25(va)-.25 G(luated before `=', b).25 E
(ut safety \214rst.)-.2 E(Going a step further)97 667.6 Q 2.5(,w)-.4 G
2.5(ec)-2.5 G(ould write the loop in the lo)-2.5 E(wer)-.25 E
(-case program as)-.2 E F1 1.5(while\( \(c=getchar\( \)\) !=)108 684.6 R
F2<a2>7.5 E F1(\\0)A F2<a2>A F1(\))7.5 E 1.5(putchar\( \()144 696.6 R F2
<a2>A F1(A)A F2<a2>A F1 1.5(<=c && c<=)B F2<a2>A F1(Z)A F2<a2>A F1 7.5
(\)?c)C F2<2da2>-7.5 E F1(A)A F2<a2>A F1(+)A F2<a2>A F1(a)A F2<a2>A F1
7.5(:c\))7.5 G(;)-7.5 E EP
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/F0 10/Times-Roman@0 SF 2.5(CT)72 36 S 182.23(utorial -)-2.95 F 2.5(7-)
2.5 G/F1 10/Courier@0 SF(If's)97 87.6 Q F0(and)2.553 E F1(else's)2.553 E
F0 .053(can be used to construct logic that branches one of se)2.553 F
-.15(ve)-.25 G .054(ral w).15 F .054(ays and then rejoins,)-.1 F 2.5(ac)
72 99.6 S(ommon programming structure, in this w)-2.5 E(ay:)-.1 E F1
(if\()108 116.6 Q/F2 16/Courier@0 SF(...)A F1(\))A({)144 128.6 Q F2(...)
A F1(})A 1.5(else if\()108 140.6 R F2(...)A F1(\))A({)144 152.6 Q F2
(...)A F1(})A 1.5(else if\()108 164.6 R F2(...)A F1(\))A({)144 176.6 Q
F2(...)A F1(})A(else)108 188.6 Q({)144 200.6 Q F2(...)A F1(})A F0 .06
(The conditions are tested in order)72 217.6 R 2.56(,a)-.4 G .06(nd e)
-2.56 F .06(xactly one block is e)-.15 F -.15(xe)-.15 G .06
(cuted _ either the \214rst one whose).15 F F1(if)2.56 E F0 .06
(is satis-)2.56 F .348(\214ed, or the one for the last)72 229.6 R F1
(else)2.848 E F2(.)A F0 .348(When this block is \214nished, the ne)5.348
F .348(xt statement e)-.15 F -.15(xe)-.15 G .348(cuted is the one af-)
.15 F(ter the last)72 241.6 Q F1(else)2.5 E F2(.)A F0
(If no action is to be tak)5 E(en for the `)-.1 E(`def)-.74 E(ault')-.1
E 2.5('c)-.74 G(ase, omit the last)-2.5 E F1(else)2.5 E F2(.)A F0 -.15
(Fo)97 257.2 S 2.5(re).15 G(xample, to count letters, digits and others\
 in a \214le, we could write)-2.65 E F1 1.5(main\( \) {)108 274.2 R 1.5
(int let, dig, other, c;)144 286.2 R 1.5(let = dig = other = 0;)144
298.2 R 1.5(while\( \(c=getchar\( \)\) !=)144 310.2 R/F3 10/Symbol SF
<a2>7.5 E F1(\\0)A F3<a2>A F1(\))7.5 E 1.5(if\( \()180 322.2 R F3<a2>A
F1(A)A F3<a2>A F1 1.5(<=c && c<=)B F3<a2>A F1(Z)A F3<a2>A .4 LW 310.88
315.45 310.88 322.2 DL 314.546 315.45 314.546 322.2 DL F1 20.666(\)\()
296.38 322.2 S F3<a2>-20.666 E F1(a)A F3<a2>A F1 1.5(<=c && c<=)B F3<a2>
A F1(z)A F3<a2>A F1 7.5(\)\))C F0(++)7.5 E F1(let;)A 1.5(else if\()180
334.2 R F3<a2>7.5 E F1(0)A F3<a2>A F1 1.5(<=c && c<=)B F3<a2>A F1(9)A F3
<a2>A F1(\))7.5 E F0(++)15 E F1(dig;)A(else)180 346.2 Q F0(++)15 E F1
(other;)A 1.5
(printf\("%d letters, %d digits, %d others\\n", let, dig, other\);)144
358.2 R(})108 370.2 Q F0(The `++' operator means `)72 387.2 Q
(`increment by 1')-.74 E('; we will get to it in the ne)-.74 E
(xt section.)-.15 E/F4 10/Times-Bold@0 SF 2.5(10. Incr)72 411.2 R
(ement and Decr)-.18 E(ement Operators)-.18 E F0 .928
(In addition to the usual `)97 426.8 R F3(-)A F0 .928(', C also has tw)B
3.427(oo)-.1 G .927
(ther interesting unary operators, `++' \(increment\) and)-3.427 F(`)72
438.8 Q F3(--)A F0 2.5('\()C 2.5(decrement\). Suppose)-2.5 F(we w)2.5 E
(ant to count the lines in a \214le.)-.1 E F1 1.5(main\( \) {)108 455.8
R 1.5(int c,n;)144 467.8 R 7.5(n=0)144 479.8 S(;)-7.5 E 1.5
(while\( \(c=getchar\( \)\) !=)144 491.8 R F3<a2>7.5 E F1(\\0)A F3<a2>A
F1(\))7.5 E 1.5(if\( c)180 503.8 R F0(==)7.5 E F3<a2>7.5 E F1(\\n)A F3
<a2>A F1(\))7.5 E F0(++)216 515.8 Q F1(n;)A 1.5
(printf\("%d lines\\n", n\);)144 527.8 R(})108 539.8 Q F0(++)72 556.8 Q
F1(n)A F0 .99(is equi)3.49 F -.25(va)-.25 G .99(lent to).25 F F1(n=n+1)
3.49 E F0 -.2(bu)3.49 G 3.49(tc).2 G(learer)-3.49 E 3.49(,p)-.4 G .99
(articularly when)-3.49 F F1(n)3.49 E F0 .99(is a complicated e)3.49 F
3.49(xpression. `++')-.15 F .99(and `)3.49 F F3(--)A F0(')A
(can be applied only to)72 568.8 Q F1(int's)2.5 E F0(and)2.5 E F1
(char's)2.5 E F0(\(and)2.5 E F1(pointers)2.5 E F0(which we ha)2.5 E -.15
(ve)-.2 G(n').15 E 2.5(tg)-.18 G(ot to yet\).)-2.5 E .76
(The unusual feature of `++' and `)97 584.4 R F3(--)A F0 3.26('i)C 3.26
(st)-3.26 G .76(hat the)-3.26 F 3.259(yc)-.15 G .759
(an be used either before or after a v)-3.259 F 3.259(ariable. The)-.25
F -.25(va)72 596.4 S .376(lue of ++).25 F F1(k)A F0 .376(is the v)2.876
F .377(alue of)-.25 F F1(k)2.877 E/F5 10/Times-Italic@0 SF(after)2.877 E
F0 .377(it has been incremented.)2.877 F .377(The v)5.377 F .377
(alue of)-.25 F F1(k)2.877 E F0 .377(++ is)B F1(k)2.877 E F5(befor)2.877
E(e)-.37 E F0 .377(it is increment-)2.877 F 2.5(ed. Suppose)72 608.4 R
F1(k)2.5 E F0(is 5.)2.5 E(Then)5 E F1 7.5(x=)108 625.4 S F0(++)A F1(k;)A
F0(increments)72 642.4 Q F1(k)2.5 E F0(to 6 and then sets)2.5 E F1(x)2.5
E F0(to the resulting v)2.5 E(alue, i.e., to 6.)-.25 E(But)5 E F1 7.5
(x=k)108 659.4 S F0(++)-7.5 E F1(;)A F0 .7(\214rst sets)72 676.4 R F1(x)
3.2 E F0 .699(to to 5, and)3.199 F F5(then)3.199 E F0(increments)3.199 E
F1(k)3.199 E F0 .699(to 6.)3.199 F .699(The incrementing ef)5.699 F .699
(fect of ++)-.25 F F1(k)A F0(and)3.199 E F1(k)3.199 E F0 .699
(++ is the same, b)B(ut)-.2 E(their v)72 688.4 Q(alues are respecti)-.25
E -.15(ve)-.25 G(ly 5 and 6.).15 E 1.6 -.8(We s)5 H(hall soon see e).8 E
(xamples where both of these uses are important.)-.15 E EP
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/F0 10/Times-Roman@0 SF 2.5(CT)72 36 S 182.23(utorial -)-2.95 F 2.5(8-)
2.5 G/F1 10/Times-Bold@0 SF 2.5(11. Arrays)72 84 R F0 .06(In C, as in F)
97 99.6 R .06(ortran or PL/I, it is possible to mak)-.15 F 2.56(ea)-.1 G
.06(rrays whose elements are basic types.)-2.56 F .06(Thus we can)5.06 F
(mak)72 111.6 Q 2.5(ea)-.1 G 2.5(na)-2.5 G(rray of 10 inte)-2.5 E
(gers with the declaration)-.15 E/F2 10/Courier@0 SF 1.5(int x[10];)108
128.6 R F0 .814(The square brack)72 145.6 R .814(ets mean)-.1 F/F3 10
/Times-Italic@0 SF(subscripting;)3.314 E F0 .814
(parentheses are used only for function references.)3.314 F .813
(Array inde)5.813 F -.15(xe)-.15 G(s).15 E(be)72 157.6 Q(gin at)-.15 E
F3(zer)2.5 E(o,)-.45 E F0(so the elements of)2.5 E F2(x)2.5 E F0(are)2.5
E F2 1.5(x[0], x[1], x[2],)108 174.6 R/F4 16/Courier@0 SF(...)7.5 E F2
7.5(,x)C([9])-7.5 E F0(If an array has)72 191.6 Q F2(n)2.5 E F0
(elements, the lar)2.5 E(gest subscript is)-.18 E F2(n)2.5 E/F5 10
/Symbol SF(-)A F2(1)A F4(.)A F0 .425(Multiple-dimension arrays are pro)
97 207.2 R .426(vided, though not much used abo)-.15 F .726 -.15(ve t)
-.15 H .626 -.1(wo d).15 H 2.926(imensions. The).1 F(declara-)2.926 E
(tion and use look lik)72 219.2 Q(e)-.1 E F2 1.5(int name[10] [20];)108
236.2 R 7.5(n=n)108 248.2 S 1.5(ame[i+j] [1] + name[k] [2];)-7.5 F F0
.213(Subscripts can be arbitrary inte)72 265.2 R .212(ger e)-.15 F 2.712
(xpressions. Multi-dimension)-.15 F .212(arrays are stored by ro)2.712 F
2.712(w\()-.25 G .212(opposite to F)-2.712 F(or)-.15 E(-)-.2 E
(tran\), so the rightmost subscript v)72 277.2 Q(aries f)-.25 E(astest;)
-.1 E F2(name)2.5 E F0(has 10 ro)2.5 E(ws and 20 columns.)-.25 E .131
(Here is a program which reads a line, stores it in a b)97 292.8 R(uf)
-.2 E(fer)-.25 E 2.631(,a)-.4 G .131(nd prints its length \(e)-2.631 F
.131(xcluding the ne)-.15 F(wline)-.25 E(at the end\).)72 304.8 Q F2 1.5
(main\( \) {)108 321.8 R 1.5(int n, c;)144 333.8 R 1.5(char line[100];)
144 345.8 R 7.5(n=0)144 357.8 S(;)-7.5 E 1.5
(while\( \(c=getchar\( \)\) !=)144 369.8 R F5<a2>7.5 E F2(\\n)A F5<a2>A
F2 7.5(\){)7.5 G 1.5(if\( n < 100 \))180 381.8 R 1.5(line[n] = c;)216
393.8 R(n)180 405.8 Q F0(++)A F2(;)A(})144 417.8 Q 1.5
(printf\("length = %d\\n", n\);)144 429.8 R(})108 441.8 Q F0 .768
(As a more complicated problem, suppose we w)97 462.4 R .767
(ant to print the count for each line in the input, still)-.1 F
(storing the \214rst 100 characters of each line.)72 474.4 Q -.35(Tr)5 G
2.5(yi).35 G 2.5(ta)-2.5 G 2.5(sa)-2.5 G 2.5(ne)-2.5 G -.15(xe)-2.65 G
(rcise before looking at the solution:).15 E F2 1.5(main\( \) {)108
491.4 R 1.5(int n, c; char line[100];)144 503.4 R 7.5(n=0)144 515.4 S(;)
-7.5 E 1.5(while\( \(c=getchar\( \)\) !=)144 527.4 R F5<a2>7.5 E F2(\\0)
A F5<a2>A F2(\))7.5 E 1.5(if\( c)180 539.4 R F0(==)7.5 E F5<a2>7.5 E F2
(\\n)A F5<a2>A F2 7.5(\){)7.5 G 1.5(printf\("%d0, n\);)216 551.4 R 7.5
(n=0)216 563.4 S(;)-7.5 E(})180 575.4 Q 1.5(else {)180 587.4 R 1.5
(if\( n < 100 \) line[n] = c;)216 599.4 R(n)216 611.4 Q F0(++)A F2(;)A
(})180 623.4 Q(})108 635.4 Q F1 2.5(12. Character)72 664.4 R
(Arrays; Strings)2.5 E F0 -1.25 -.7(Te x)97 680 T 3.507(ti).7 G 3.507
(su)-3.507 G 1.007(sually k)-3.507 F 1.007
(ept as an array of characters, as we did with)-.1 F F2 -2.492(line[ ])
3.508 F F0 1.008(in the e)3.508 F 1.008(xample abo)-.15 F -.15(ve)-.15 G
6.008(.B).15 G(y)-6.008 E(con)72 692 Q -.15(ve)-.4 G .101(ntion in C, t\
he last character in a character array should be a `\\0' because most p\
rograms that manipu-).15 F .936(late character arrays e)72 704 R .936
(xpect it.)-.15 F -.15(Fo)5.936 G 3.436(re).15 G(xample,)-3.586 E F2
(printf)3.437 E F0 .937
(uses the `\\0' to detect the end of a character array)3.437 F EP
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/F0 10/Times-Roman@0 SF 2.5(CT)72 36 S 182.23(utorial -)-2.95 F 2.5(9-)
2.5 G(when printing it out with a `%s'.)72 84 Q 1.6 -.8(We c)97 99.6 T
(an cop).8 E 2.5(yac)-.1 G(haracter array)-2.5 E/F1 10/Courier@0 SF(s)
2.5 E F0(into another)2.5 E F1(t)2.5 E F0(lik)2.5 E 2.5(et)-.1 G(his:)
-2.5 E F1 7.5(i=0)144 116.6 S(;)-7.5 E 1.5(while\( \(t[i]=s[i]\) !=)144
128.6 R/F2 10/Symbol SF<a2>7.5 E F1(\\0)A F2<a2>A F1(\))7.5 E(i)180
140.6 Q F0(++)A F1(;)A F0 .054(Most of the time we ha)97 161.2 R .354
-.15(ve t)-.2 H 2.554(op).15 G .054(ut in our o)-2.554 F .054
(wn `\\0' at the end of a string; if we w)-.25 F .054
(ant to print the line with)-.1 F F1(printf,)72 173.2 Q F0(it')2.5 E 2.5
(sn)-.55 G(ecessary)-2.5 E 5(.T)-.65 G
(his code prints the character count before the line:)-5 E F1 1.5
(main\( \) {)108 190.2 R 1.5(int n;)144 202.2 R 1.5(char line[100];)144
214.2 R 7.5(n=0)144 226.2 S(;)-7.5 E 1.5(while\( \(line[n)144 238.2 R F0
(++)A F1 1.5(]=getchar\( \)\) !=)B F2<a2>7.5 E F1(\\n)A F2<a2>A F1(\);)
7.5 E 1.5(line[n] =)144 250.2 R F2<a2>7.5 E F1(\\0)A F2<a2>A F1(;)A 1.5
(printf\("%d:\\t%s", n, line\);)144 262.2 R(})108 274.2 Q F0 .393
(Here we increment)72 291.2 R F1(n)2.893 E F0 .393
(in the subscript itself, b)2.893 F .393(ut only after the pre)-.2 F
.394(vious v)-.25 F .394(alue has been used.)-.25 F .394(The character)
5.394 F(is read, placed in)72 303.2 Q F1(line[n],)2.5 E F0
(and only then)2.5 E F1(n)2.5 E F0(is incremented.)2.5 E .16(There is o\
ne place and one place only where C puts in the `\\0' at the end of a c\
haracter array for you,)97 318.8 R(and that is in the construction)72
330.8 Q F1 1.5("stuff between double quotes")108 347.8 R F0 1.277
(The compiler puts a `\\0' at the end automatically)72 364.8 R 6.277(.T)
-.65 G -.15(ex)-6.977 G 3.777(te).15 G 1.277
(nclosed in double quotes is called a)-3.777 F/F3 10/Times-Italic@0 SF
(string;)3.778 E F0(its)3.778 E(properties are precisely those of an \(\
initialized\) array of characters.)72 376.8 Q/F4 10/Times-Bold@0 SF 2.5
(13. F)72 400.8 R(or Statement)-.25 E F0(The)97 416.4 Q F1(for)2.657 E
F0 .157(statement is a some)2.657 F .157(what generalized)-.25 F F1
(while)2.657 E F0 .156
(that lets us put the initialization and increment)2.657 F
(parts of a loop into a single statement along with the test.)72 428.4 Q
(The general form of the)5 E F1(for)2.5 E F0(is)2.5 E F1 1.5
(for\( initialization; expression; increment \))108 445.4 R(statement)
144 457.4 Q F0(The meaning is e)72 474.4 Q(xactly)-.15 E F1
(initialization;)144 491.4 Q 1.5(while\( expression \) {)144 503.4 R
(statement)180 515.4 Q(increment;)180 527.4 Q(})144 539.4 Q F0
(Thus, the follo)72 556.4 Q(wing code does the same array cop)-.25 E 2.5
(ya)-.1 G 2.5(st)-2.5 G(he e)-2.5 E(xample in the pre)-.15 E
(vious section:)-.25 E F1 1.5(for\( i=0; \(t[i]=s[i]\) !=)144 573.4 R F2
<a2>7.5 E F1(\\0)A F2<a2>A F1 7.5(;i)C F0(++)-7.5 E F1(\);)7.5 E F0
(This slightly more ornate e)72 590.4 Q
(xample adds up the elements of an array:)-.15 E F1 1.5(sum = 0;)144
607.4 R 1.5(for\( i=0; i<n; i)144 619.4 R F0(++)A F1(\))A 1.5
(sum = sum + array[i];)180 631.4 R F0 .316(In the)97 652 R F1(for)2.816
E F0 .316(statement, the initialization can be left out if you w)2.816 F
.316(ant, b)-.1 F .317(ut the semicolon has to be there.)-.2 F .751
(The increment is also optional.)72 664 R .751(It is)5.751 F F3(not)
3.251 E F0(follo)3.251 E .751(wed by a semicolon.)-.25 F .75
(The second clause, the test, w)5.75 F .75(orks the)-.1 F .468(same w)72
676 R .468(ay as in the)-.1 F F1(while:)2.968 E F0 .468(if the e)2.968 F
.469(xpression is true \(not zero\) do another loop, otherwise get on w\
ith the)-.15 F(ne)72 688 Q .209(xt statement.)-.15 F .209(As with the)
5.209 F F1(while,)2.709 E F0(the)2.709 E F1(for)2.709 E F0 .208
(loop may be done zero times.)2.709 F .208(If the e)5.208 F .208
(xpression is left out, it)-.15 F(is tak)72 700 Q(en to be al)-.1 E -.1
(wa)-.1 G(ys true, so).1 E F1 1.5(for\( ; ; \))108 717 R/F5 16/Courier@0
SF(...)7.5 E EP
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/F0 10/Times-Roman@0 SF 3.125(CT)72 36 S 178.48(utorial -)-3.575 F .625
(10 -)3.125 F(and)72 84 Q/F1 10/Courier@0 SF 1.5(while\( 1 \))108 101 R
/F2 16/Courier@0 SF(...)7.5 E F0(are both in\214nite loops.)72 118 Q
-1.1(Yo)97 133.6 S 3.161(um)1.1 G .661(ight ask wh)-3.161 F 3.161(yw)
-.05 G 3.161(eu)-3.161 G .661(se a)-3.161 F F1(for)3.161 E F0 .661
(since it')3.161 F 3.161(ss)-.55 G 3.161(om)-3.161 G .661(uch lik)-3.161
F 3.161(ea)-.1 G F1(while)A F2(.)A F0(\(Y)5.661 E .661
(ou might also ask wh)-1.1 F 3.161(yw)-.05 G(e)-3.161 E 1.571(use a)72
145.6 R F1(while)4.071 E F0 4.071(because...\) The)4.071 F F1(for)4.071
E F0 1.571(is usually preferable because it k)4.071 F 1.57
(eeps the code where it')-.1 F 4.07(su)-.55 G 1.57(sed and)-4.07 F .033
(sometimes eliminates the need for compound statements, as in this code\
 that zeros a tw)72 157.6 R .033(o-dimensional array:)-.1 F F1 1.5
(for\( i=0; i<n; i)108 174.6 R F0(++)A F1(\))7.5 E 1.5
(for\( j=0; j<m; j)144 186.6 R F0(++)A F1(\))7.5 E 1.5(array[i][j] = 0;)
180 198.6 R/F3 10/Times-Bold@0 SF 2.5(14. Functions;)72 227.6 R
(Comments)2.5 E F0 .01(Suppose we w)97 243.2 R .01
(ant, as part of a lar)-.1 F .009
(ger program, to count the occurrences of the ascii characters in some)
-.18 F .378(input te)72 255.2 R 2.879(xt. Let)-.15 F .379
(us also map ille)2.879 F -.05(ga)-.15 G 2.879(lc).05 G .379
(haracters \(those with v)-2.879 F .379(alue>127 or <0\) into one pile.)
-.25 F .379(Since this is pre-)5.379 F .515(sumably an isolated part of\
 the program, good practice dictates making it a separate function.)72
267.2 R .514(Here is one)5.514 F -.1(wa)72 279.2 S(y:).1 E F1 1.5
(main\( \) {)108 296.2 R 1.5(int hist[129];)144 308.2 R(/)58.5 E/F4 14
/Courier@0 SF(*)4.9 I F1 1.5(128 legal chars + 1 illegal group)7.5 -4.9
N F4(*)7.5 4.9 M F1(/)-4.9 I F2(...)144 320.2 Q F1 1.5
(count\(hist, 128\);)144 332.2 R(/)4.5 E F4(*)4.9 I F1 1.5
(count the letters into hist)7.5 -4.9 N F4(*)7.5 4.9 M F1(/)-4.9 I
(printf\()144 344.2 Q F2(...)7.5 E F1 40.2(\); /)7.5 F F4(*)4.9 I F1 1.5
(comments look like this; use them)7.5 -4.9 N F4(*)7.5 4.9 M F1(/)-4.9 I
F2(...)144 356.2 Q F1(/)43.2 E F4(*)4.9 I F1 1.5
(anywhere blanks, tabs or newlines could appear)7.5 -4.9 N F4(*)7.5 4.9
M F1(/)-4.9 I(})108 368.2 Q 1.5(count\(buf, size\))108 385.2 R 1.5
(int size, buf[ ]; {)130.5 397.2 R 1.5(int i, c;)144 409.2 R 1.5
(for\( i=0; i<=size; i)144 421.2 R F0(++)A F1(\))7.5 E 1.5(buf[i] = 0;)
180 433.2 R(/)75 E F4(*)4.9 I F1 1.5(set buf to zero)7.5 -4.9 N F4(*)7.5
4.9 M F1(/)-4.9 I 1.5(while\( \(c=getchar\( \)\) !=)144 445.2 R/F5 10
/Symbol SF<a2>7.5 E F1(\\0)A F5<a2>A F1 -4.94 7.5(\){ /)7.5 H F4(*)-7.5
4.9 M F1 1.5(read til eof)7.5 -4.9 N F4(*)7.5 4.9 M F1(/)-4.9 I .4 LW
265 450.45 265 457.2 DL 268.666 450.45 268.666 457.2 DL 1.5
(if\( c > size)180 457.2 R 7.5(c<0\))20.666 G 7.5(c=s)216 469.2 S 45
(ize; /)-7.5 F F4(*)4.9 I F1 1.5(fix illegal input)7.5 -4.9 N F4(*)7.5
4.9 M F1(/)-4.9 I(buf[c])180 481.2 Q F0(++)A F1(;)A(})144 493.2 Q
(return;)144 505.2 Q(})108 517.2 Q F0 2.891 -.8(We h)72 534.2 T -2.25
-.2(av e).8 H 1.291(already seen man)3.991 F 3.791(ye)-.15 G 1.291
(xamples of calling a function, so let us concentrate on ho)-3.941 F
3.791(wt)-.25 G(o)-3.791 E/F6 10/Times-Italic@0 SF(de\214ne)3.792 E F0
(one.)3.792 E(Since)72 546.2 Q F1(count)2.84 E F0 .34(has tw)2.84 F 2.84
(oa)-.1 G -.18(rg)-2.84 G .34(uments, we need to declare them, as sho)
.18 F .34(wn, gi)-.25 F .34(ving their types, and in the case of)-.25 F
F1(buf,)72 558.2 Q F0 .205(the f)2.705 F .206(act that it is an array)
-.1 F 5.206(.T)-.65 G .206(he declarations of ar)-5.206 F .206
(guments go)-.18 F F6(between)2.706 E F0 .206(the ar)2.706 F .206
(gument list and the open-)-.18 F(ing `{'.)72 570.2 Q
(There is no need to specify the size of the array)5 E F1(buf,)2.5 E F0
(for it is de\214ned outside of)2.5 E F1(count)2.5 E F2(.)A F0(The)97
585.8 Q F1(return)2.752 E F0 .251
(statement simply says to go back to the calling routine.)2.752 F .251
(In f)5.251 F .251(act, we could ha)-.1 F .551 -.15(ve o)-.2 H(mitted)
.15 E(it, since a return is implied at the end of a function.)72 597.8 Q
.233(What if we w)97 613.4 R(anted)-.1 E F1(count)2.733 E F0 .233
(to return a v)2.733 F .233(alue, say the number of characters read?)
-.25 F(The)5.233 E F1(return)2.733 E F0(state-)2.733 E(ment allo)72
625.4 Q(ws for this too:)-.25 E F1 1.5(int i, c, nchar;)144 642.4 R 1.5
(nchar = 0;)144 654.4 R F2(...)144 666.4 Q F1 1.5
(while\( \(c=getchar\( \)\) !=)144 678.4 R F5<a2>7.5 E F1(\\0)A F5<a2>A
F1 7.5(\){)7.5 G 265 683.65 265 690.4 DL 268.666 683.65 268.666 690.4 DL
1.5(if\( c > size)180 690.4 R 7.5(c<0\))20.666 G 7.5(c=s)216 702.4 S
(ize;)-7.5 E(buf[c])180 714.4 Q F0(++)A F1(;)A(nchar)180 726.4 Q F0(++)A
F1(;)A EP
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/F0 10/Courier@0 SF 7.5(CT)72 36 S(utorial)-7.5 E/F1 10/Symbol SF(-)
153.51 E F0(11)7.5 E F1(-)7.5 E F0(})144 84 Q(return\(nchar\);)144 96 Q
/F2 10/Times-Roman@0 SF(An)72 113 Q 2.564(ye)-.15 G .064
(xpression can appear within the parentheses.)-2.714 F .063
(Here is a function to compute the minimum of tw)5.064 F 2.563(oi)-.1 G
(nte-)-2.563 E(gers:)72 125 Q F0 1.5(min\(a, b\))108 142 R 1.5
(int a, b; {)130.5 154 R 1.5(return\( a < b ? a : b \);)144 166 R(})108
178 Q F2 1.6 -.8(To c)97 202.2 T(op).8 E 2.5(yac)-.1 G(haracter array)
-2.5 E 2.5(,w)-.65 G 2.5(ec)-2.5 G(ould write the function)-2.5 E F0 1.5
(strcopy\(s1, s2\))108 219.2 R(/)52.5 E/F3 14/Courier@0 SF(*)4.9 I F0
1.5(copies s1 to s2)7.5 -4.9 N F3(*)7.5 4.9 M F0(/)-4.9 I 1.5
(char s1[ ], s2[ ]; {)130.5 231.2 R 1.5(int i;)144 243.2 R 1.5
(for\( i = 0; \(s2[i] = s1[i]\) !=)144 255.2 R F1<a2>7.5 E F0(\\0)A F1
<a2>A F0 7.5(;i)C F2(++)-7.5 E F0(\);)7.5 E(})108 267.2 Q F2 1.316
(As is often the case, all the w)72 284.2 R 1.316(ork is done by the as\
signment statement embedded in the test part of the)-.1 F F0(for)72
296.2 Q/F4 16/Courier@0 SF(.)A F2(Ag)5.943 E .943
(ain, the declarations of the ar)-.05 F(guments)-.18 E F0(s1)3.442 E F2
(and)3.442 E F0(s2)3.442 E F2 .942(omit the sizes, because the)3.442 F
3.442(yd)-.15 G(on')-3.442 E 3.442(tm)-.18 G .942(atter to)-3.442 F F0
(strcopy)72 308.2 Q F4(.)A F2
(\(In the section on pointers, we will see a more ef)5 E(\214cient w)
-.25 E(ay to do a string cop)-.1 E -.65(y.)-.1 G(\)).65 E .871(There is\
 a subtlety in function usage which can trap the unsuspecting F)97 323.8
R .872(ortran programmer)-.15 F 5.872(.S)-.55 G(imple)-5.872 E -.25(va)
72 335.8 S .733(riables \(not arrays\) are passed in C by `).25 F .733
(`call by v)-.74 F(alue')-.25 E .732
(', which means that the called function is gi)-.74 F -.15(ve)-.25 G
3.232(na).15 G(cop)72 347.8 Q 3.14(yo)-.1 G 3.14(fi)-3.14 G .64(ts ar)
-3.14 F .64(guments, and doesn')-.18 F 3.14(tk)-.18 G(no)-3.14 E 3.14
(wt)-.25 G .641(heir addresses.)-3.14 F .641(This mak)5.641 F .641
(es it impossible to change the v)-.1 F .641(alue of)-.25 F
(one of the actual input ar)72 359.8 Q(guments.)-.18 E .163
(There are tw)97 375.4 R 2.663(ow)-.1 G .162(ays out of this dilemma.)
-2.763 F .162(One is to mak)5.162 F 2.662(es)-.1 G .162
(pecial arrangements to pass to the function)-2.662 F .098
(the address of a v)72 387.4 R .098(ariable instead of its v)-.25 F
2.598(alue. The)-.25 F .098(other is to mak)2.598 F 2.598(et)-.1 G .098
(he v)-2.598 F .098(ariable a global or e)-.25 F .098(xternal v)-.15 F
(ariable,)-.25 E(which is kno)72 399.4 Q
(wn to each function by its name.)-.25 E 1.6 -.8(We w)5 H
(ill discuss both possibilities in the ne).8 E(xt fe)-.15 E 2.5(ws)-.25
G(ections.)-2.5 E/F5 10/Times-Bold@0 SF 2.5(15. Local)72 423.4 R
(and Exter)2.5 E(nal V)-.15 E(ariables)-.92 E F2(If we say)97 439 Q F0
1.5(f\( \) {)108 456 R 1.5(int x;)144 468 R F4(...)144 480 Q F0(})108
492 Q 1.5(g\( \) {)108 504 R 1.5(int x;)144 516 R F4(...)144 528 Q F0(})
108 540 Q F2(each)72 557 Q F0(x)2.983 E F2(is)2.983 E/F6 10
/Times-Italic@0 SF(local)2.982 E F2 .482(to its o)2.982 F .482
(wn routine _ the)-.25 F F0(x)2.982 E F2(in)2.982 E F0(f)2.982 E F2 .482
(is unrelated to the)2.982 F F0(x)2.982 E F2(in)2.982 E F0(g)2.982 E F4
(.)A F2 .482(\(Local v)5.482 F .482(ariables are also called)-.25 F -.74
(``)72 569 S(automatic').74 E 3.274('.\) Furthermore)-.74 F .774
(each local v)3.274 F .774
(ariable in a routine appears only when the function is called, and)-.25
F F6(disappear)72 581 Q(s)-.1 E F2 .016(when the function is e)2.516 F
2.516(xited. Local)-.15 F -.25(va)2.516 G .016(riables ha).25 F .316
-.15(ve n)-.2 H 2.516(om).15 G .015(emory from one call to the ne)-2.516
F .015(xt and must)-.15 F .306(be e)72 593 R .306
(xplicitly initialized upon each entry)-.15 F 5.306(.\()-.65 G .306
(There is a)-5.306 F F0(static)2.806 E F2 .307
(storage class for making local v)2.806 F .307(ariables with)-.25 F
(memory; we w)72 605 Q(on')-.1 E 2.5(td)-.18 G(iscuss it.\))-2.5 E .198
(As opposed to local v)97 620.6 R(ariables,)-.25 E F6 -.2(ex)2.698 G
.197(ternal variables).2 F F2 .197(are de\214ned e)2.697 F .197
(xternal to all functions, and are \(poten-)-.15 F .417(tially\) a)72
632.6 R -.25(va)-.2 G .418(ilable to all functions.).25 F .418
(External storage al)5.418 F -.1(wa)-.1 G .418(ys remains in e).1 F
2.918(xistence. T)-.15 F 2.918(om)-.8 G(ak)-2.918 E 2.918(ev)-.1 G .418
(ariables e)-3.168 F(xternal)-.15 E(we ha)72 644.6 Q .3 -.15(ve t)-.2 H
(o).15 E F6(de\214ne)2.5 E F2(them e)2.5 E
(xternal to all functions, and, where)-.15 E -.15(ve)-.25 G 2.5(rw).15 G
2.5(ew)-2.5 G(ant to use them, mak)-2.6 E 2.5(ea)-.1 G F6(declar)A
(ation.)-.15 E F0 1.5(main\( \) {)108 661.6 R 1.5
(extern int nchar, hist[ ];)144 673.6 R F4(...)144 685.6 Q F0 1.5
(count\( \);)144 697.6 R F4(...)144 709.6 Q F0(})108 721.6 Q EP
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153.51 E F0(12)7.5 E F1(-)7.5 E F0 1.5(count\( \) {)108 89 R 1.5
(extern int nchar, hist[ ];)144 101 R 1.5(int i, c;)144 113 R/F2 16
/Courier@0 SF(...)144 125 Q F0(})108 137 Q 12(int hist[129];)108 154 R
(/)12 E/F3 14/Courier@0 SF(*)4.9 I F0 1.5(space for histogram)7.5 -4.9 N
F3(*)7.5 4.9 M F0(/)-4.9 I 12(int nchar;)108 166 R(/)72 E F3(*)4.9 I F0
1.5(character count)7.5 -4.9 N F3(*)7.5 4.9 M F0(/)-4.9 I/F4 10
/Times-Roman@0 SF .442(Roughly speaking, an)72 183 R 2.942(yf)-.15 G
.441(unction that wishes to access an e)-2.942 F .441(xternal v)-.15 F
.441(ariable must contain an)-.25 F F0(extern)2.941 E F4(decla-)2.941 E
.176(ration for it.)72 195 R .176
(The declaration is the same as others, e)5.176 F .176
(xcept for the added k)-.15 F -.15(ey)-.1 G -.1(wo).15 G(rd).1 E F0
(extern)2.677 E F2(.)A F4(Furthermore,)5.177 E(there must some)72 207 Q
(where be a)-.25 E/F5 10/Times-Italic@0 SF(de\214nition)2.5 E F4
(of the e)2.5 E(xternal v)-.15 E(ariables e)-.25 E
(xternal to all functions.)-.15 E .822(External v)97 222.6 R .822
(ariables can be initialized; the)-.25 F 3.322(ya)-.15 G .822
(re set to zero if not e)-3.322 F .822(xplicitly initialized.)-.15 F
.821(In its simplest)5.822 F
(form, initialization is done by putting the v)72 234.6 Q
(alue \(which must be a constant\) after the de\214nition:)-.25 E F0 12
(int nchar)108 251.6 R(0;)6 E 6(char flag)108 263.6 R F1<a2>12 E F0(f)A
F1<a2>A F0(;)A F4(etc)114.25 275.6 Q/F6 16/Times-Roman@0 SF(.)A F4
(This is discussed further in a later section.)72 292.6 Q 1.165(This en\
ds our discussion of what might be called the central core of C.)97
313.2 R -1.1(Yo)6.166 G 3.666(un)1.1 G 1.666 -.25(ow h)-3.666 H -2.25
-.2(av e).25 H 1.166(enough to)3.866 F .493
(write quite substantial C programs, and it w)72 325.2 R .492
(ould probably be a good idea if you paused long enough to do)-.1 F 2.5
(so. The)72 337.2 R(rest of this tutorial will describe some more ornat\
e constructions, useful b)2.5 E(ut not essential.)-.2 E/F7 10
/Times-Bold@0 SF 2.5(16. P)72 371.2 R(ointers)-.2 E F4(A)97 386.8 Q F5
(pointer)3.187 E F4 .687(in C is the address of something.)3.187 F .688
(It is a rare case indeed when we care what the speci\214c)5.687 F .037
(address itself is, b)72 398.8 R .037(ut pointers are a quite common w)
-.2 F .037(ay to get at the contents of something.)-.1 F .036
(The unary opera-)5.036 F(tor `&' is used to produce the address of an \
object, if it has one. Thus)72 410.8 Q F0 1.5(int a, b;)144 427.8 R 7.5
(b=&)144 439.8 S(a;)-7.5 E F4 .201(puts the address of)72 456.8 R F0(a)
2.701 E F4(into)2.701 E F0(b)2.701 E F2(.)A F4 1.801 -.8(We c)5.201 H
(an').8 E 2.701(td)-.18 G 2.701(om)-2.701 G .201(uch with it e)-2.701 F
.202(xcept print it or pass it to some other routine, be-)-.15 F .097
(cause we ha)72 468.8 R -.15(ve)-.2 G(n').15 E 2.597(tg)-.18 G -2.15
-.25(iv e)-2.597 H(n).25 E F0(b)2.597 E F4 .097
(the right kind of declaration.)2.597 F .096(But if we declare that)
5.096 F F0(b)2.596 E F4 .096(is indeed a)2.596 F F5(pointer)2.596 E F4
.096(to an in-)2.596 F(te)72 480.8 Q(ger)-.15 E 2.5(,w)-.4 G(e')-2.5 E
(re in good shape:)-.5 E F0 1.5(int a,)144 497.8 R F3(*)7.5 4.9 M F0 1.5
(b, c;)-4.9 J 7.5(b=&)144 509.8 S(a;)-7.5 E 7.5(c=)144 521.8 S F3(*)4.9
I F0(b;)-4.9 I(b)72 538.8 Q F4 .13(contains the address of)2.63 F F0(a)
2.631 E F4(and)2.631 E F0 -3.369(`c =)2.631 F F3(*)2.631 4.9 M F0(b')
-4.9 I F4 .131(means to use the v)2.631 F .131(alue in)-.25 F F0(b)2.631
E F4 .131(as an address, i.e., as a pointer)2.631 F 5.131(.T)-.55 G(he)
-5.131 E(ef)72 550.8 Q .078(fect is that we get back the contents of)
-.25 F F0(a,)2.578 E F4 .078(albeit rather indirectly)2.578 F 5.078(.\()
-.65 G(It')-5.078 E 2.578(sa)-.55 G -.1(lwa)-2.578 G .078
(ys the case that).1 F F0(`)2.578 E F3(*)4.9 I F0(&x')-4.9 I F4 .078
(is the)2.578 F(same as)72 562.8 Q F0(x)2.5 E F4(if)2.5 E F0(x)2.5 E F4
(has an address.\))2.5 E .618
(The most frequent use of pointers in C is for w)97 578.4 R .618
(alking ef)-.1 F .618(\214ciently along arrays.)-.25 F .618(In f)5.618 F
.618(act, in the imple-)-.1 F .176(mentation of an array)72 590.4 R
2.676(,t)-.65 G .175(he array name represents the address of the zeroth\
 element of the array)-2.676 F 2.675(,s)-.65 G 2.675(oy)-2.675 G .175
(ou can')-2.675 F(t)-.18 E .508(use it on the left side of an e)72 602.4
R 3.008(xpression. \(Y)-.15 F .508(ou can')-1.1 F 3.008(tc)-.18 G .508
(hange the address of something by assigning to it.\))-3.008 F(If)5.508
E(we say)72 614.4 Q F0(char)108 631.4 Q F3(*)7.5 4.9 M F0(y;)-4.9 I 1.5
(char x[100];)108 643.4 R(y)72 660.4 Q F4 .538
(is of type pointer to character \(although it doesn')3.038 F 3.038(ty)
-.18 G .538(et point an)-3.038 F 3.038(ywhere\). W)-.15 F 3.038(ec)-.8 G
.538(an mak)-3.038 F(e)-.1 E F0(y)3.038 E F4 .538(point to an ele-)3.038
F(ment of)72 672.4 Q F0(x)2.5 E F4(by either of)2.5 E F0 7.5(y=&)108
689.4 S(x[0];)-7.5 E 7.5(y=x)108 701.4 S(;)-7.5 E EP
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(x[0])2.5 E F0(this is le)2.5 E -.05(ga)-.15 G 2.5(la).05 G
(nd consistent.)-2.5 E(No)97 99.6 Q(w)-.25 E F1(`)2.5 E/F2 14/Courier@0
SF(*)4.9 I F1(y')-4.9 I F0(gi)2.5 E -.15(ve)-.25 G(s).15 E F1(x[0])2.5 E
/F3 16/Courier@0 SF(.)A F0(More importantly)5 E(,)-.65 E F2(*)108 121.5
Q F1 27.6(\(y+1\) gives)-4.9 J(x[1])7.5 E F2(*)108 133.5 Q F1 27.6
(\(y+i\) gives)-4.9 J(x[i])7.5 E F0(and the sequence)72 145.6 Q F1 7.5
(y=&)144 162.6 S(x[0];)-7.5 E(y)144 174.6 Q F0(++)A F1(;)A F0(lea)72
191.6 Q -.15(ve)-.2 G(s).15 E F1(y)2.5 E F0(pointing at)2.5 E F1(x[1])
2.5 E F3(.)A F0(Let')97 207.2 Q 3.643(su)-.55 G 1.143
(se pointers in a function)-3.643 F F1(length)3.643 E F0 1.143
(that computes ho)3.643 F 3.643(wl)-.25 G 1.144
(ong a character array is.)-3.643 F(Remember)6.144 E 1.156(that by con)
72 219.2 R -.15(ve)-.4 G 1.155
(ntion all character arrays are terminated with a `\\0'.).15 F 1.155
(\(And if the)6.155 F 3.655(ya)-.15 G(ren')-3.655 E 1.155
(t, this program will)-.18 F(blo)72 231.2 Q 2.5(wu)-.25 G 2.5(pi)-2.5 G
(ne)-2.5 E(vitably)-.25 E 2.5(.\) The)-.65 F(old w)2.5 E(ay:)-.1 E F1
(length\(s\))108 248.2 Q 1.5(char s[ ]; {)130.5 260.2 R 1.5(int n;)144
272.2 R 1.5(for\( n=0; s[n] !=)144 284.2 R/F4 10/Symbol SF<a2>7.5 E F1
(\\0)A F4<a2>A F1 7.5(;\))C(n)180 296.2 Q F0(++)A F1(;)A(return\(n\);)
144 308.2 Q(})108 320.2 Q F0(Re)72 337.2 Q(writing with pointers gi)-.25
E -.15(ve)-.25 G(s).15 E F1(length\(s\))108 354.2 Q(char)130.5 366.2 Q
F2(*)7.5 4.9 M F1 1.5(s; {)-4.9 J 1.5(int n;)144 378.2 R 1.5(for\( n=0;)
144 390.2 R F2(*)7.5 4.9 M F1 7.5(s!)-4.9 K(=)-7.5 E F4<a2>7.5 E F1(\\0)
A F4<a2>A F1 7.5(;s)C F0(++)-7.5 E F1(\))7.5 E(n)180 402.2 Q F0(++)A F1
(;)A(return\(n\);)144 414.2 Q(})108 426.2 Q F0 -1.1(Yo)72 443.2 S 2.751
(uc)1.1 G .251(an no)-2.751 F 2.751(ws)-.25 G .251(ee wh)-2.751 F 2.751
(yw)-.05 G 2.751(eh)-2.751 G -2.25 -.2(av e)-2.751 H .251
(to say what kind of thing)2.951 F F1(s)2.751 E F0 .251
(points to _ if we')2.751 F .252(re to increment it with)-.5 F F1(s)
2.752 E F0 .252(++ we)B(ha)72 455.2 Q .3 -.15(ve t)-.2 H 2.5(oi).15 G
(ncrement it by the right amount.)-2.5 E(The pointer v)97 470.8 Q
(ersion is more ef)-.15 E(\214cient \(this is almost al)-.25 E -.1(wa)
-.1 G(ys true\) b).1 E(ut e)-.2 E -.15(ve)-.25 G 2.5(nm).15 G
(ore compact is)-2.5 E F1 1.5(for\( n=0;)144 487.8 R F2(*)7.5 4.9 M F1
(s)-4.9 I F0(++)A F1(!=)7.5 E F4<a2>7.5 E F1(\\0)A F4<a2>A F1 7.5(;n)C
F0(++)-7.5 E F1(\);)7.5 E F0(The)72 504.8 Q F1(`)3.303 E F2(*)4.9 I F1
(s')-4.9 I F0 .803(returns a character; the)3.303 F F1(`)3.303 E F0(++)A
F1(')A F0 .803(increments the pointer so we')3.303 F .803(ll get the ne)
-.1 F .803(xt character ne)-.15 F .802(xt time)-.15 F 2.915(around. As)
72 516.8 R .415(you can see, as we mak)2.915 F 2.915(et)-.1 G .415
(hings more ef)-2.915 F .415(\214cient, we also mak)-.25 F 2.915(et)-.1
G .416(hem less clear)-2.915 F 5.416(.B)-.55 G(ut)-5.416 E F1(`)2.916 E
F2(*)4.9 I F1(s)-4.9 I F0(++)A F1(')A F0(is)2.916 E
(an idiom so common that you ha)72 528.8 Q .3 -.15(ve t)-.2 H 2.5(ok).15
G(no)-2.5 E 2.5(wi)-.25 G(t.)-2.5 E(Going a step further)97 544.4 Q 2.5
(,h)-.4 G(ere')-2.5 E 2.5(so)-.55 G(ur function)-2.5 E F1(strcopy)2.5 E
F0(that copies a character array)2.5 E F1(s)2.5 E F0(to another)2.5 E F1
(t)2.5 E F3(.)A F1(strcopy\(s,t\))108 561.4 Q(char)130.5 573.4 Q F2(*)
7.5 4.9 M F1(s,)-4.9 I F2(*)7.5 4.9 M F1 1.5(t; {)-4.9 J(while\()144
585.4 Q F2(*)4.9 I F1(t)-4.9 I F0(++)A F1(=)7.5 E F2(*)7.5 4.9 M F1(s)
-4.9 I F0(++)A F1(\);)A(})108 597.4 Q F0 2.032 -.8(We h)72 614.4 T -2.25
-.2(av e).8 H .431(omitted the test ag)3.131 F .431(ainst `\\0', becaus\
e `\\0' is identically zero; you will often see the code this w)-.05 F
(ay)-.1 E(.)-.65 E(\(Y)72 626.4 Q(ou)-1.1 E/F5 10/Times-Italic@0 SF
(must)2.5 E F0(ha)2.5 E .3 -.15(ve a s)-.2 H
(pace after the `=': see section 25.\)).15 E -.15(Fo)97 642 S 2.5(ra).15
G -.18(rg)-2.5 G(uments to a function, and there only).18 E 2.5(,t)-.65
G(he declarations)-2.5 E F1 1.5(char s[ ];)108 659 R(char)108 671 Q F2
(*)7.5 4.9 M F1(s;)-4.9 I F0(are equi)72 688 Q -.25(va)-.25 G(lent _ a \
pointer to a type, or an array of unspeci\214ed size of that type, are \
the same thing.).25 E .068(If this all seems mysterious, cop)97 703.6 R
2.568(yt)-.1 G .068(hese forms until the)-2.568 F 2.568(yb)-.15 G .068
(ecome second nature.)-2.568 F -1.1(Yo)5.068 G 2.568(ud)1.1 G(on')-2.568
E 2.569(to)-.18 G .069(ften need)-2.569 F(an)72 715.6 Q
(ything more complicated.)-.15 E EP
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/F0 10/Times-Roman@0 SF 2.5(CT)72 36 S 179.73(utorial -)-2.95 F(14 -)2.5
E/F1 10/Times-Bold@0 SF 2.5(17. Function)72 84 R(Ar)2.5 E(guments)-.1 E
F0 .262(Look back at the function)97 99.6 R/F2 10/Courier@0 SF(strcopy)
2.761 E F0 .261(in the pre)2.761 F .261(vious section.)-.25 F 1.861 -.8
(We p)5.261 H .261(assed it tw).8 F 2.761(os)-.1 G .261
(tring names as ar)-2.761 F(gu-)-.18 E .277
(ments, then proceeded to clobber both of them by incrementation.)72
111.6 R .277(So ho)5.277 F 2.777(wc)-.25 G .277(ome we don')-2.777 F
2.777(tl)-.18 G .277(ose the original)-2.777 F
(strings in the function that called)72 123.6 Q F2(strcopy?)2.5 E F0
.562(As we said before, C is a `)97 139.2 R .562(`call by v)-.74 F
(alue')-.25 E 3.062('l)-.74 G .562(anguage: when you mak)-3.062 F 3.062
(eaf)-.1 G .562(unction call lik)-3.062 F(e)-.1 E F2(f\(x\),)3.062 E F0
(the)3.062 E/F3 10/Times-Italic@0 SF(value)72 151.2 Q F0(of)2.859 E F2
(x)2.859 E F0 .359(is passed, not its address.)2.859 F .359(So there')
5.359 F 2.859(sn)-.55 G 2.86(ow)-2.859 G .36(ay to)-2.96 F F3(alter)2.86
E F2(x)2.86 E F0 .36(from inside)2.86 F F2(f)2.86 E/F4 16/Courier@0 SF
(.)A F0(If)5.36 E F2(x)2.86 E F0 .36(is an array)2.86 F F2(\(char)2.86 E
(x[10]\))72 163.2 Q F0 .262(this isn')2.762 F 2.762(tap)-.18 G .262
(roblem, because)-2.762 F F2(x)2.762 E F3(is)2.762 E F0 .262
(an address an)2.762 F(yw)-.15 E(ay)-.1 E 2.762(,a)-.65 G .261(nd you')
-2.762 F .261(re not trying to change it, just what)-.5 F .223
(it addresses.)72 175.2 R .223(This is wh)5.223 F(y)-.05 E F2(strcopy)
2.723 E F0 -.1(wo)2.723 G .223(rks as it does.).1 F .223(And it')5.223 F
2.723(sc)-.55 G(on)-2.723 E -.15(ve)-.4 G .223(nient not to ha).15 F
.523 -.15(ve t)-.2 H 2.724(ow).15 G .224(orry about mak-)-2.824 F
(ing temporary copies of the input ar)72 187.2 Q(guments.)-.18 E .014
(But what if)97 202.8 R F2(x)2.514 E F0 .014(is a scalar and you do w)
2.514 F .014(ant to change it?)-.1 F .014(In that case, you ha)5.014 F
.313 -.15(ve t)-.2 H 2.513(op).15 G .013(ass the)-2.513 F F3(addr)2.513
E(ess)-.37 E F0(of)2.513 E F2(x)2.513 E F0(to)72 214.8 Q F2(f,)2.5 E F0
(and then use it as a pointer)2.5 E 5(.T)-.55 G(hus for e)-5 E
(xample, to interchange tw)-.15 E 2.5(oi)-.1 G(nte)-2.5 E
(gers, we must write)-.15 E F2 1.5(flip\(x, y\))108 231.8 R(int)130.5
243.8 Q/F5 14/Courier@0 SF(*)7.5 4.9 M F2(x,)-4.9 I F5(*)7.5 4.9 M F2
1.5(y; {)-4.9 J 1.5(int temp;)144 255.8 R 1.5(temp =)144 267.8 R F5(*)
7.5 4.9 M F2(x;)-4.9 I F5(*)144 284.7 Q F2 7.5(x=)-4.9 K F5(*)4.9 I F2
(y;)-4.9 I F5(*)144 296.7 Q F2 7.5(y=t)-4.9 K(emp;)-7.5 E(})108 303.8 Q
F0(and to call)72 320.8 Q F2(flip,)2.5 E F0(we ha)2.5 E .3 -.15(ve t)-.2
H 2.5(op).15 G(ass the addresses of the v)-2.5 E(ariables:)-.25 E F2 1.5
(flip \(&a, &b\);)108 337.8 R F1 2.5(18. Multiple)72 366.8 R(Le)2.5 E
-.1(ve)-.15 G(ls of P).1 E(ointers; Pr)-.2 E(ogram Ar)-.18 E(guments)-.1
E F0 .196(When a C program is called, the ar)97 382.4 R .197
(guments on the command line are made a)-.18 F -.25(va)-.2 G .197
(ilable to the main pro-).25 F .765(gram as an ar)72 394.4 R .765
(gument count)-.18 F F2(argc)3.265 E F0 .764
(and an array of character strings)3.265 F F2(argv)3.264 E F0 .764
(containing the ar)3.264 F 3.264(guments. Ma-)-.18 F 1.598
(nipulating these ar)72 406.4 R 1.598
(guments is one of the most common uses of multiple le)-.18 F -.15(ve)
-.25 G 1.598(ls of pointers \(`).15 F 1.599(`pointer to)-.74 F .866
(pointer to ...)72 418.4 R -.74('')-.7 G 3.366(\). By).74 F(con)3.366 E
-.15(ve)-.4 G(ntion,).15 E F2(argc)3.366 E F0 .866
(is greater than zero; the \214rst ar)3.366 F .866(gument \(in)-.18 F F2
(argv[0]\))3.366 E F0 .865(is the com-)3.366 F(mand name itself.)72
430.4 Q(Here is a program that simply echoes its ar)97 446 Q(guments.)
-.18 E F2 1.5(main\(argc, argv\))108 463 R 1.5(int argc;)130.5 475 R
(char)130.5 487 Q F5(**)7.5 4.9 M F2 1.5(argv; {)-4.9 J 1.5(int i;)144
499 R 1.5(for\( i=1; i < argc; i)144 511 R F0(++)A F2(\))7.5 E 1.5
(printf\("%s ", argv[i]\);)180 523 R(putchar\()144 535 Q/F6 10/Symbol SF
<a2>A F2(\\n)A F6<a2>A F2(\);)A(})108 547 Q F0 .245(Step by step:)72 564
R F2(main)2.745 E F0 .245(is called with tw)2.745 F 2.745(oa)-.1 G -.18
(rg)-2.745 G .245(uments, the ar).18 F .245
(gument count and the array of ar)-.18 F(guments.)-.18 E F2(argv)5.245 E
F0(is)2.745 E 2.525(ap)72 576 S .024(ointer to an array)-2.525 F 2.524
(,w)-.65 G .024(hose indi)-2.524 F .024
(vidual elements are pointers to arrays of characters.)-.25 F .024
(The zeroth ar)5.024 F .024(gument is)-.18 F .794(the name of the comma\
nd itself, so we start to print with the \214rst ar)72 588 R .794
(gument, until we')-.18 F 1.095 -.15(ve p)-.5 H .795(rinted them all.)
.15 F(Each)72 600 Q F2(argv[i])2.5 E F0(is a character array)2.5 E 2.5
(,s)-.65 G 2.5(ow)-2.5 G 2.5(eu)-2.5 G(se a)-2.5 E F2(`%s')2.5 E F0
(in the)2.5 E F2(printf)2.5 E F4(.)A F0 -1.1(Yo)97 615.6 S 2.5(uw)1.1 G
(ill sometimes see the declaration of)-2.5 E F2(argv)2.5 E F0
(written as)2.5 E F2(char)108 632.6 Q F5(*)7.5 4.9 M F2 1.5(argv[ ];)
-4.9 J F0 .082(which is equi)72 649.6 R -.25(va)-.25 G 2.582(lent. But)
.25 F .082(we can')2.582 F 2.582(tu)-.18 G(se)-2.582 E F2 -3.418
(char argv[ ][ ],)2.582 F F0 .082(because both dimensions are v)2.582 F
.081(ariable and there)-.25 F -.1(wo)72 661.6 S(uld be no w).1 E
(ay to \214gure out ho)-.1 E 2.5(wb)-.25 G(ig the array is.)-2.5 E
(Here')97 677.2 Q 2.508(sab)-.55 G .008(igger e)-2.508 F .008
(xample using)-.15 F F2(argc)2.508 E F0(and)2.508 E F2(argv)2.508 E F4
(.)A F0 2.508(Ac)5.008 G .008(ommon con)-2.508 F -.15(ve)-.4 G .009
(ntion in C programs is that if the).15 F 1.648(\214rst ar)72 689.2 R
1.648(gument is `)-.18 F F6(-)A F0 1.648
(', it indicates a \215ag of some sort.)B -.15(Fo)6.648 G 4.148(re).15 G
1.648(xample, suppose we w)-4.298 F 1.648(ant a program to be)-.1 F
(callable as)72 701.2 Q F2(prog)108 718.2 Q F6(-)7.5 E F2 1.5
(abc arg1 arg2)B F4(...)7.5 E EP
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/F0 10/Times-Roman@0 SF 3.125(CT)72 36 S 178.48(utorial -)-3.575 F .625
(15 -)3.125 F(where the `)72 84 Q/F1 10/Symbol SF(-)A F0 2.5('a)C -.18
(rg)-2.5 G(ument is optional; if it is present, it may be follo).18 E
(wed by an)-.25 E 2.5(yc)-.15 G(ombination of a, b, and c.)-2.5 E/F2 10
/Courier@0 SF 1.5(main\(argc, argv\))108 101 R 1.5(int argc;)130.5 113 R
(char)130.5 125 Q/F3 14/Courier@0 SF(**)7.5 4.9 M F2 1.5(argv; {)-4.9 J
/F4 16/Courier@0 SF(...)144 137 Q F2 1.5(aflag = bflag = cflag)144 149 R
7.5(=0)15 G(;)-7.5 E 1.5(if\( argc > 1 && argv[1][0])144 161 R F0(==)7.5
E F1<a22da2>7.5 E F2 7.5(\){)7.5 G 1.5(for\( i=1; \(c=argv[1][i]\) !=)
180 173 R F1<a2>7.5 E F2(\\0)A F1<a2>A F2 7.5(;i)C F0(++)-7.5 E F2(\))
7.5 E 1.5(if\( c)216 185 R F0(==)A F1<a2>A F2(a)A F1<a2>A F2(\))7.5 E
(aflag)252 197 Q F0(++)A F2(;)A 1.5(else if\( c)216 209 R F0(==)A F1<a2>
A F2(b)A F1<a2>A F2(\))7.5 E(bflag)252 221 Q F0(++)A F2(;)A 1.5
(else if\( c)216 233 R F0(==)A F1<a2>A F2(c)A F1<a2>A F2(\))7.5 E(cflag)
252 245 Q F0(++)A F2(;)A(else)216 257 Q 1.5(printf\("%c?\\n", c\);)252
269 R F1(--)180 281 Q F2(argc;)A F0(++)180 293 Q F2(argv;)A(})144 305 Q
F4(...)144 317 Q F0 .217(There are se)97 337.6 R -.15(ve)-.25 G .217
(ral things w).15 F .217(orth noticing about this code.)-.1 F .217
(First, there is a real need for the left-to-right)5.217 F -.25(eva)72
349.6 S .823(luation that && pro).25 F .823(vides; we don')-.15 F 3.323
(tw)-.18 G .823(ant to look at)-3.423 F F2(argv[1])3.323 E F0 .823
(unless we kno)3.323 F 3.323(wi)-.25 G(t')-3.323 E 3.323(st)-.55 G 3.323
(here. Second,)-3.323 F(the)3.322 E(statements)72 361.6 Q F1(--)144
378.6 Q F2(argc;)A F0(++)144 390.6 Q F2(argv;)A F0 .002
(let us march along the ar)72 407.6 R .003
(gument list by one position, so we can skip o)-.18 F -.15(ve)-.15 G
2.503(rt).15 G .003(he \215ag ar)-2.503 F .003(gument as if it had ne)
-.18 F -.15(ve)-.25 G(r).15 E -.15(ex)72 419.6 S 1.053(isted _ the rest\
 of the program is independent of whether or not there w).15 F 1.052
(as a \215ag ar)-.1 F 3.552(gument. This)-.18 F(only)3.552 E -.1(wo)72
431.6 S(rks because).1 E F2(argv)2.5 E F0
(is a pointer which can be incremented.)2.5 E/F5 10/Times-Bold@0 SF 2.5
(19. The)72 455.6 R(Switch Statement; Br)2.5 E(eak; Continue)-.18 E F0
(The)97 471.2 Q F2(switch)2.659 E F0 .159
(statement can be used to replace the multi-w)2.659 F .16
(ay test we used in the last e)-.1 F 2.66(xample. When)-.15 F
(the tests are lik)72 483.2 Q 2.5(et)-.1 G(his:)-2.5 E F2 1.5(if\( c)108
500.2 R F0(==)7.5 E F1<a2>7.5 E F2(a)A F1<a2>A F2(\))7.5 E F4(...)7.5 E
F2 1.5(else if\( c)108 512.2 R F0(==)7.5 E F1<a2>7.5 E F2(b)A F1<a2>A F2
(\))7.5 E F4(...)7.5 E F2 1.5(else if\( c)108 524.2 R F0(==)7.5 E F1<a2>
7.5 E F2(c)A F1<a2>A F2(\))7.5 E F4(...)7.5 E F2(else)108 536.2 Q F4
(...)7.5 E F0 .882(testing a v)72 553.2 R .882(alue ag)-.25 F .882
(ainst a series of)-.05 F/F6 10/Times-Italic@0 SF(constants,)3.382 E F0
.882(the switch statement is often clearer and usually gi)3.382 F -.15
(ve)-.25 G 3.381(sb).15 G(etter)-3.381 E 2.5(code. Use)72 565.2 R
(it lik)2.5 E 2.5(et)-.1 G(his:)-2.5 E F2 1.5(switch\( c \) {)108 582.2
R(case)108 606.2 Q F1<a2>7.5 E F2(a)A F1<a2>A F2(:)A(aflag)144 618.2 Q
F0(++)A F2(;)A(break;)144 630.2 Q(case)108 642.2 Q F1<a2>7.5 E F2(b)A F1
<a2>A F2(:)A(bflag)144 654.2 Q F0(++)A F2(;)A(break;)144 666.2 Q(case)
108 678.2 Q F1<a2>7.5 E F2(c)A F1<a2>A F2(:)A(cflag)144 690.2 Q F0(++)A
F2(;)A(break;)144 702.2 Q(default:)108 714.2 Q 1.5
(printf\("%c?\\n", c\);)144 726.2 R EP
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/F0 10/Courier@0 SF 7.5(CT)72 36 S(utorial)-7.5 E/F1 10/Symbol SF(-)
153.51 E F0(16)7.5 E F1(-)7.5 E F0(break;)144 84 Q(})108 96 Q/F2 10
/Times-Roman@0 SF(The)72 113 Q F0(case)2.764 E F2 .264
(statements label the v)2.764 F .264(arious actions we w)-.25 F(ant;)-.1
E F0(default)2.764 E F2 .265(gets done if none of the other cases are)
2.764 F 3.071(satis\214ed. \(A)72 125 R F0(default)3.071 E F2 .571
(is optional; if it isn')3.071 F 3.071(tt)-.18 G .571
(here, and none of the cases match, you just f)-3.071 F .571
(all out the bot-)-.1 F(tom.\))72 137 Q(The)97 152.6 Q F0(break)3.152 E
F2 .652(statement in this e)3.152 F .652(xample is ne)-.15 F 4.452 -.65
(w. I)-.25 H 3.152(ti).65 G 3.152(st)-3.152 G .652
(here because the cases are just labels, and after)-3.152 F .587
(you do one of them, you)72 164.6 R/F3 10/Times-Italic@0 SF .587
(fall thr)3.087 F(ough)-.45 E F2 .587(to the ne)3.087 F .587
(xt unless you tak)-.15 F 3.087(es)-.1 G .586(ome e)-3.087 F .586
(xplicit action to escape.)-.15 F .586(This is a)5.586 F(mix)72 176.6 Q
.368(ed blessing.)-.15 F .369(On the positi)5.368 F .669 -.15(ve s)-.25
H .369(ide, you can ha).15 F .669 -.15(ve m)-.2 H .369
(ultiple cases on a single statement; we might w).15 F .369(ant to)-.1 F
(allo)72 188.6 Q 2.5(wb)-.25 G(oth upper and lo)-2.5 E
(wer case letters in our \215ag \214eld, so we could say)-.25 E F0(case)
108 205.6 Q F1<a2>7.5 E F0(a)A F1<a2>A F0 15(:c)C(ase)-15 E F1<a2>7.5 E
F0(A)A F1<a2>A F0(:)A/F4 16/Courier@0 SF(...)32.12 E F0(case)108 222.6 Q
F1<a2>7.5 E F0(b)A F1<a2>A F0 15(:c)C(ase)-15 E F1<a2>7.5 E F0(B)A F1
<a2>A F0(:)A F4(...)32.12 E F0(etc)115.5 234.6 Q F4(.)A F2 .549
(But what if we just w)72 251.6 R .548(ant to get out after doing)-.1 F
F0 -2.952(case `a')3.048 F F2 5.548(?W)3.048 G 3.048(ec)-6.348 G .548
(ould get out of a)-3.048 F F0(case)3.048 E F2 .548(of the)3.048 F F0
(switch)3.048 E F2 .284(with a label and a)72 263.6 R F0(goto,)2.784 E
F2 -.2(bu)2.784 G 2.784(tt).2 G .284(his is really ugly)-2.784 F 5.285
(.T)-.65 G(he)-5.285 E F0(break)2.785 E F2 .285(statement lets us e)
2.785 F .285(xit without either)-.15 F F0(goto)2.785 E F2(or)2.785 E
(label.)72 275.6 Q F0 1.5(switch\( c \) {)108 292.6 R(case)108 316.6 Q
F1<a2>7.5 E F0(a)A F1<a2>A F0(:)A(aflag)144 328.6 Q F2(++)A F0(;)A
(break;)144 340.6 Q(case)108 352.6 Q F1<a2>7.5 E F0(b)A F1<a2>A F0(:)A
(bflag)144 364.6 Q F2(++)A F0(;)A(break;)144 376.6 Q F4(...)120 388.6 Q
F0(})108 400.6 Q(/)108 412.6 Q/F5 14/Courier@0 SF(*)4.9 I F0 1.5
(the break statements get us here directly)7.5 -4.9 N F5(*)7.5 4.9 M F0
(/)-4.9 I F2(The)72 429.6 Q F0(break)3.553 E F2 1.053(statement also w)
3.553 F 1.053(orks in)-.1 F F0(for)3.553 E F2(and)3.553 E F0(while)3.553
E F2 1.053(statements _ it causes an immediate e)3.553 F 1.053
(xit from the)-.15 F(loop.)72 441.6 Q(The)97 457.2 Q F0(continue)3.187 E
F2 .687(statement w)3.187 F(orks)-.1 E F3(only)3.187 E F2(inside)3.187 E
F0(for's)3.187 E F2(and)3.187 E F0(while's;)3.187 E F2 .687
(it causes the ne)3.187 F .688(xt iteration of)-.15 F .026
(the loop to be started.)72 469.2 R .026
(This means it goes to the increment part of the)5.026 F F0(for)2.525 E
F2 .025(and the test part of the)2.525 F F0(while)2.525 E F4(.)A F2 1.72
-.8(We c)72 481.2 T .12(ould ha).8 F .42 -.15(ve u)-.2 H .12(sed a).15 F
F0(continue)2.62 E F2 .12(in our e)2.62 F .12
(xample to get on with the ne)-.15 F .121(xt iteration of the)-.15 F F0
(for,)2.621 E F2 -.2(bu)2.621 G 2.621(ti).2 G 2.621(ts)-2.621 G(eems)
-2.621 E(clearer to use)72 493.2 Q F0(break)2.5 E F2(instead.)2.5 E/F6
10/Times-Bold@0 SF 2.5(20. Structur)72 517.2 R(es)-.18 E F2 1.248(The m\
ain use of structures is to lump together collections of disparate v)97
532.8 R 1.247(ariable types, so the)-.25 F 3.747(yc)-.15 G(an)-3.747 E
(con)72 544.8 Q -.15(ve)-.4 G .309(niently be treated as a unit.).15 F
-.15(Fo)5.309 G 2.809(re).15 G .309
(xample, if we were writing a compiler or assembler)-2.959 F 2.809(,w)
-.4 G 2.809(em)-2.809 G .309(ight need)-2.809 F .842
(for each identi\214er information lik)72 556.8 R 3.342(ei)-.1 G .842
(ts name \(a character array\), its source line number \(an inte)-3.342
F .841(ger\), some)-.15 F(type information \(a character)72 568.8 Q 2.5
(,p)-.4 G(erhaps\), and probably a usage count \(another inte)-2.5 E
(ger\).)-.15 E F0 6(char id[10];)144 585.8 R 12(int line;)144 597.8 R 6
(char type;)144 609.8 R 12(int usage;)144 621.8 R F2 1.866 -.8(We c)97
642.4 T .266(an mak).8 F 2.766(eas)-.1 G .266
(tructure out of this quite easily)-2.766 F 5.266(.W)-.65 G 2.767<658c>
-6.066 G .267(rst tell C what the structure will look lik)-2.767 F .267
(e, that)-.1 F .223(is, what kinds of things it contains; after that we\
 can actually reserv)72 654.4 R 2.722(es)-.15 G .222
(torage for it, either in the same state-)-2.722 F(ment or separately)72
666.4 Q 5(.T)-.65 G
(he simplest thing is to de\214ne it and allocate storage all at once:)
-5 E F0 1.5(struct {)108 683.4 R 6(char id[10];)144 695.4 R 12
(int line;)144 707.4 R 6(char type;)144 719.4 R 12(int usage;)144 731.4
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/F0 10/Courier@0 SF 7.5(CT)72 36 S(utorial)-7.5 E/F1 10/Symbol SF(-)
153.51 E F0(17)7.5 E F1(-)7.5 E F0 7.5(}s)108 84 S(ym;)-7.5 E/F2 10
/Times-Roman@0 SF .104(This de\214nes)97 104.6 R F0(sym)2.604 E F2 .105
(to be a structure with the speci\214ed shape;)2.604 F F0 -3.395
(id, line, type)2.605 F F2(and)2.605 E F0(usage)2.605 E F2(are)2.605 E
/F3 10/Times-Italic@0 SF(mem-)2.605 E(ber)72 116.6 Q(s)-.1 E F2
(of the structure.)2.5 E(The w)5 E(ay we refer to an)-.1 E 2.5(yp)-.15 G
(articular member of the structure is)-2.5 E F0(structure-name)108 133.6
Q/F4 16/Courier@0 SF(.)7.5 E F0(member)7.5 E F2(as in)72 150.6 Q F0(sym)
144 167.6 Q F4(.)A F0 1.5(type = 077;)B 1.5(if\( sym)144 179.6 R F4(.)A
F0(usage)A F2(==)7.5 E F0 7.5(0\))7.5 G F4(...)A F0 1.5(while\( sym)144
191.6 R F4(.)A F0(id[j)A F2(++)A F0 7.5(]\))C F4(...)A F2(etc)153.375
203.6 Q/F5 16/Times-Roman@0 SF(.)A F2 .839
(Although the names of structure members ne)72 220.6 R -.15(ve)-.25 G
3.339(rs).15 G .839(tand alone, the)-3.339 F 3.339(ys)-.15 G .839
(till ha)-3.339 F 1.139 -.15(ve t)-.2 H 3.339(ob).15 G 3.339(eu)-3.339 G
.839(nique _ there can')-3.339 F 3.338(tb)-.18 G(e)-3.338 E(another)72
232.6 Q F0(id)2.5 E F2(or)2.5 E F0(usage)2.5 E F2
(in some other structure.)2.5 E .575(So f)97 248.2 R .575(ar we ha)-.1 F
-.15(ve)-.2 G(n').15 E 3.075(tg)-.18 G .575(ained much.)-3.125 F .575
(The adv)5.575 F .575(antages of structures start to come when we ha)
-.25 F .876 -.15(ve a)-.2 H .576(rrays of).15 F 1.004
(structures, or when we w)72 260.2 R 1.003
(ant to pass complicated data layouts between functions.)-.1 F 1.003
(Suppose we w)6.003 F 1.003(anted to)-.1 F(mak)72 272.2 Q 2.5(eas)-.1 G
(ymbol table for up to 100 identi\214ers.)-2.5 E 1.6 -.8(We c)5 H
(ould e).8 E(xtend our de\214nitions lik)-.15 E(e)-.1 E F0 6
(char id[100][10];)144 289.2 R 12(int line[100];)144 301.2 R 6
(char type[100];)144 313.2 R 12(int usage[100];)144 325.2 R F2 -.2(bu)72
342.2 S 2.595(tas).2 G .096(tructure lets us rearrange this spread-out \
information so all the data about a single identifer is collect-)-2.595
F(ed into one lump:)72 354.2 Q F0 1.5(struct {)108 371.2 R 6
(char id[10];)144 383.2 R 12(int line;)144 395.2 R 6(char type;)144
407.2 R 12(int usage;)144 419.2 R 7.5(}s)108 431.2 S(ym[100];)-7.5 E F2
.835(This mak)72 448.2 R(es)-.1 E F0(sym)3.335 E F2 .835
(an array of structures; each array element has the speci\214ed shape.)
3.335 F(No)5.835 E 3.335(ww)-.25 G 3.335(ec)-3.335 G .835(an refer to)
-3.335 F(members as)72 460.2 Q F0(sym[i])144 477.2 Q F4(.)A F0(usage)A
F2(++)A F0 15.12(;/)C/F6 14/Courier@0 SF(*)-15.12 4.9 M F0 1.5
(increment usage of i-th identifier)7.5 -4.9 N F6(*)7.5 4.9 M F0(/)-4.9
I 1.5(for\( j=0; sym[i])144 489.2 R F4(.)A F0(id[j)A F2(++)A F0 7.5(]!)C
(=)-7.5 E F1<a2>7.5 E F0(\\0)A F1<a2>A F0 7.5(;\))C F4(...)A F2(etc)
153.375 501.2 Q F5(.)A F2
(Thus to print a list of all identi\214ers that ha)72 518.2 Q -.15(ve)
-.2 G(n').15 E 2.5(tb)-.18 G(een used, together with their line number)
-2.5 E(,)-.4 E F0 1.5(for\( i=0; i<nsym; i)144 535.2 R F2(++)A F0(\))7.5
E 1.5(if\( sym[i])180 547.2 R F4(.)A F0(usage)A F2(==)7.5 E F0 7.5(0\))
7.5 G 1.5(printf\("%d\\t%s\\n", sym[i])216 559.2 R F4(.)A F0 1.5
(line, sym[i])B F4(.)A F0(id\);)A F2 .2(Suppose we no)97 579.8 R 2.7(ww)
-.25 G .2(ant to write a function)-2.8 F F0(lookup\(name\))2.7 E F2 .2
(which will tell us if)2.7 F F0(name)2.7 E F2 .2(already e)2.7 F(xists)
-.15 E(in)72 591.8 Q F0(sym,)2.612 E F2 .112(by gi)2.612 F .112
(ving its inde)-.25 F .112(x, or that it doesn')-.15 F .111
(t, by returning a)-.18 F F1(-)2.611 E F2 2.611(1. W)B 2.611(ec)-.8 G
(an')-2.611 E 2.611(tp)-.18 G .111(ass a structure to a function di-)
-2.611 F(rectly _ we ha)72 603.8 Q .3 -.15(ve t)-.2 H 2.5(oe).15 G
(ither de\214ne it e)-2.5 E(xternally)-.15 E 2.5(,o)-.65 G 2.5(rp)-2.5 G
(ass a pointer to it.)-2.5 E(Let')5 E 2.5(st)-.55 G(ry the \214rst w)
-2.5 E(ay \214rst.)-.1 E F0 12(int nsym)108 620.8 R 18(0; /)12 F F6(*)
4.9 I F0 1.5(current length of symbol table)7.5 -4.9 N F6(*)7.5 4.9 M F0
(/)-4.9 I 1.5(struct {)108 637.8 R 6(char id[10];)144 649.8 R 12
(int line;)144 661.8 R 6(char type;)144 673.8 R 12(int usage;)144 685.8
R 7.5(}s)108 697.8 S 34.5(ym[100]; /)-7.5 F F6(*)4.9 I F0 1.5
(symbol table)7.5 -4.9 N F6(*)7.5 4.9 M F0(/)-4.9 I 1.5(main\( \) {)108
714.8 R F4(...)144 726.8 Q EP
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/F0 10/Courier@0 SF 7.5(CT)72 36 S(utorial)-7.5 E/F1 10/Symbol SF(-)
153.51 E F0(18)7.5 E F1(-)7.5 E F0 1.5
(if\( \(index = lookup\(newname\)\) >= 0 \))144 84 R(sym[index])180 96 Q
/F2 16/Courier@0 SF(.)A F0(usage)A/F3 10/Times-Roman@0 SF(++)A F0 63.12
(;/)C/F4 14/Courier@0 SF(*)-63.12 4.9 M F0 1.5(already there)7.5 -4.9 N
F2(...)7.5 E F4(*)7.5 4.9 M F0(/)-4.9 I(else)144 108 Q 1.5
(install\(newname, newline, newtype\);)180 120 R F2(...)144 132 Q F0(})
108 144 Q(lookup\(s\))108 161 Q(char)130.5 173 Q F4(*)7.5 4.9 M F0 1.5
(s; {)-4.9 J 1.5(int i;)144 185 R 1.5(extern struct {)144 197 R 6
(char id[10];)180 209 R 12(int line;)180 221 R 6(char type;)180 233 R 12
(int usage;)180 245 R 7.5(}s)144 257 S 1.5(ym[ ];)-7.5 F 1.5
(for\( i=0; i<nsym; i)144 274 R F3(++)A F0(\))7.5 E 1.5
(if\( compar\(s, sym[i])180 286 R F2(.)A F0 1.5(id\) > 0 \))B
(return\(i\);)216 298 Q(return\()144 310 Q F1(-)A F0(1\);)A(})108 322 Q
60(compar\(s1,s2\) /)108 346 R F4(*)4.9 I F0 1.5(return 1 if s1)15 -4.9
N F3(==)A F0 1.5(s2, 0 otherwise)B F4(*)7.5 4.9 M F0(/)-4.9 I(char)130.5
358 Q F4(*)7.5 4.9 M F0(s1,)-4.9 I F4(*)7.5 4.9 M F0 1.5(s2; {)-4.9 J
(while\()144 370 Q F4(*)7.5 4.9 M F0(s1)-4.9 I F3 5(++ ==)B F4(*)7.5 4.9
M F0 1.5(s2 \))-4.9 J(if\()180 382 Q F4(*)7.5 4.9 M F0(s2)-4.9 I F3 5
(++ ==)B F1<a2>7.5 E F0(\\0)A F1<a2>A F0(\))7.5 E(return\(1\);)216 394 Q
(return\(0\);)144 406 Q(})108 418 Q F3 1.046
(The declaration of the structure in)72 435 R F0(lookup)3.546 E F3(isn')
3.546 E 3.546(tn)-.18 G 1.047(eeded if the e)-3.546 F 1.047
(xternal de\214nition precedes its use in the)-.15 F
(same source \214le, as we shall see in a moment.)72 447 Q(No)97 462.6 Q
2.5(ww)-.25 G(hat if we w)-2.5 E(ant to use pointers?)-.1 E F0 9
(struct symtag)108 479.6 R({)7.5 E 6(char id[10];)144 491.6 R 12
(int line;)144 503.6 R 6(char type;)144 515.6 R 12(int usage;)144 527.6
R 7.5(}s)108 539.6 S(ym[100],)-7.5 E F4(*)7.5 4.9 M F0(psym;)-4.9 I 1.5
(psym = &sym[0];)144 563.6 R(/)15 E F4(*)4.9 I F0 1.5(or p = sym;)7.5
-4.9 N F4(*)7.5 4.9 M F0(/)-4.9 I F3 .198(This mak)72 580.6 R(es)-.1 E
F0(psym)2.698 E F3 2.698(ap)2.698 G .197(ointer to our kind of structur\
e \(the symbol table\), then initializes it to point to the \214rst)
-2.698 F(element of)72 592.6 Q F0(sym)2.5 E F2(.)A F3 1.218
(Notice that we added something after the w)97 608.2 R(ord)-.1 E F0
(struct:)3.718 E F3 3.718(a`)3.718 G(`tag')-4.458 E 3.718('c)-.74 G
(alled)-3.718 E F0(symtag)3.718 E F2(.)A F3 1.218(This puts a)6.218 F
.547(name on our structure de\214nition so we can refer to it later wit\
hout repeating the de\214nition.)72 620.2 R(It')5.546 E 3.046(sn)-.55 G
.546(ot neces-)-3.046 F(sary b)72 632.2 Q(ut useful.)-.2 E(In f)5 E
(act we could ha)-.1 E .3 -.15(ve s)-.2 H(aid).15 E F0 30(struct symtag)
108 649.2 R({)7.5 E F2(...)144 661.2 Q F0 1.5(structure definition)7.5 F
(};)108 673.2 Q F3(which w)72 690.2 Q(ouldn')-.1 E 2.5(th)-.18 G -2.25
-.2(av e)-2.5 H(assigned an)2.7 E 2.5(ys)-.15 G
(torage at all, and then said)-2.5 E F0 30(struct symtag sym[100];)108
707.2 R 30(struct symtag)108 719.2 R F4(*)36 4.9 M F0(psym;)-4.9 I EP
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/F0 10/Times-Roman@0 SF 3.125(CT)72 36 S 178.48(utorial -)-3.575 F .625
(19 -)3.125 F(which w)72 84 Q(ould de\214ne the array and the pointer)
-.1 E 5(.T)-.55 G(his could be condensed further)-5 E 2.5(,t)-.4 G(o)
-2.5 E/F1 10/Courier@0 SF 30(struct symtag sym[100],)108 101 R/F2 14
/Courier@0 SF(*)7.5 4.9 M F1(psym;)-4.9 I F0(The w)97 121.6 Q
(ay we actually refer to an member of a structure by a pointer is lik)
-.1 E 2.5(et)-.1 G(his:)-2.5 E F1(ptr)144 138.6 Q/F3 10/Symbol SF(-)7.5
E F1 7.5(>s)C(tructure-member)-7.5 E F0 .039(The symbol `)72 155.6 R F3
(-)A F0 .039(>' means we')B .039
(re pointing at a member of a structure; `)-.5 F F3(-)A F0 .039
(>' is only used in that conte)B(xt.)-.15 E F1(ptr)5.039 E F0(is)2.539 E
3.375(ap)72 167.6 S .875(ointer to the \(base of\) a structure that con\
tains the structure member)-3.375 F 5.874(.T)-.55 G .874(he e)-5.874 F
(xpression)-.15 E F1(ptr)3.374 E F3(-)A F1(>struc-)A(ture-member)72
179.6 Q F0 1.241
(refers to the indicated member of the pointed-to structure.)3.741 F
1.242(Thus we ha)6.242 F 1.542 -.15(ve c)-.2 H(onstructions).15 E(lik)72
191.6 Q(e:)-.1 E F1(psym)108 208.6 Q F3(-)A F1 1.5(>type = 1;)B(psym)108
220.6 Q F3(-)A F1 1.5(>id[0] =)B F3<a2>7.5 E F1(a)A F3<a2>A F1(;)A F0
(and so on.)72 237.6 Q -.15(Fo)97 253.2 S 2.532(rm).15 G .032
(ore complicated pointer e)-2.532 F .032(xpressions, it')-.15 F 2.532
(sw)-.55 G .032(ise to use parentheses to mak)-2.532 F 2.532(ei)-.1 G
2.532(tc)-2.532 G .031(lear who goes with)-2.532 F 2.5(what. F)72 265.2
R(or e)-.15 E(xample,)-.15 E F1 1.5(struct { int x,)108 282.2 R F2(*)7.5
4.9 M F1 1.5(y; })-4.9 J F2(*)7.5 4.9 M F1(p;)-4.9 I(p)108 294.2 Q F3(-)
A F1(>x)A F0(++)A F1 1.5(increments x)1.23 F F0(++)108 306.2 Q F1(p)A F3
(-)A F1 -4.77(>x so)B 1.5(does this!)7.5 F(\()108 318.2 Q F0(++)A F1
(p\))A F3(-)A F1 19.23(>x increments)B 7.5(pb)7.5 G 1.5(efore getting x)
-7.5 F F2(*)108 335.1 Q F1(p)-4.9 I F3(-)A F1(>y)A F0(++)A F1 1.5
(uses y as a pointer, then increments it)28.83 F F2(*)108 347.1 Q F1
(\(p)-4.9 I F3(-)A F1(>y\))A F0(++)A F1 1.5(so does this)16.83 F F2(*)
108 359.1 Q F1(\(p)-4.9 I F0(++)A F1(\))A F3(-)A F1 10.83(>y uses)B 7.5
(ya)7.5 G 7.5(sap)-7.5 G 1.5(ointer, then increments p)-7.5 F F0 .376
(The w)72 371.2 R .376(ay to remember these is that)-.1 F F3(-)2.876 E
F1 -3.124(>, .)B F0(\(dot\),)5.376 E F1 6.377(\(\))2.876 G F0(and)-3.5 E
F1 6.377([])2.877 G F0 .377(bind v)-3.5 F .377(ery tightly)-.15 F 5.377
(.A)-.65 G 2.877(ne)-5.377 G .377(xpression in)-3.027 F -.2(vo)-.4 G
(lving).2 E(one of these is treated as a unit.)72 383.2 Q F1(p)5 E F3(-)
A F1 -3.5(>x, a[i], y)B/F4 16/Courier@0 SF(.)A F1(x)A F0(and)2.5 E F1
(f\(b\))2.5 E F0(are names e)2.5 E(xactly as)-.15 E F1(abc)2.5 E F0(is.)
2.5 E(If)97 398.8 Q F1(p)2.878 E F0 .378
(is a pointer to a structure, an)2.878 F 2.878(ya)-.15 G .378
(rithmetic on)-2.878 F F1(p)2.877 E F0(tak)2.877 E .377
(es into account the acutal size of the structure.)-.1 F -.15(Fo)72
410.8 S 3.561(ri).15 G(nstance,)-3.561 E F1(p)3.561 E F0 1.061
(++ increments)B F1(p)3.561 E F0 1.061
(by the correct amount to get the ne)3.561 F 1.061
(xt element of the array of structures.)-.15 F .252(But don')72 422.8 R
2.752(ta)-.18 G .252(ssume that the size of a structure is the sum of t\
he sizes of its members _ because of alignments)-2.752 F(of dif)72 434.8
Q(ferent sized objects, there may be `)-.25 E(`holes')-.74 E 2.5('i)-.74
G 2.5(nas)-2.5 G(tructure.)-2.5 E(Enough theory)97 450.4 Q 2.5(.H)-.65 G
(ere is the lookup e)-2.5 E(xample, this time with pointers.)-.15 E F1
1.5(struct symtag {)108 467.4 R 6(char id[10];)144 479.4 R 12(int line;)
144 491.4 R 6(char type;)144 503.4 R 12(int usage;)144 515.4 R 7.5(}s)
108 527.4 S(ym[100];)-7.5 E 1.5(main\( \) {)108 544.4 R 1.5
(struct symtag)144 556.4 R F2(*)7.5 4.9 M F1 1.5(lookup\( \);)-4.9 J 1.5
(struct symtag)144 568.4 R F2(*)7.5 4.9 M F1(psym;)-4.9 I F4(...)144
580.4 Q F1 1.5(if\( \(psym = lookup\(newname\)\) \))144 592.4 R(/)30 E
F2(*)4.9 I F1(non)7.5 -4.9 M F3(-)A F1 1.5(zero pointer)B F2(*)7.5 4.9 M
F1(/)-4.9 I(psym)180 604.4 Q F3(-)7.5 E F1 7.5(>u)C(sage)-7.5 E F0(++)A
F1 46.23(;/)C F2(*)-46.23 4.9 M F1 1.5(means already there)7.5 -4.9 N F2
(*)7.5 4.9 M F1(/)-4.9 I(else)144 616.4 Q 1.5
(install\(newname, newline, newtype\);)180 628.4 R F4(...)144 640.4 Q F1
(})108 652.4 Q 1.5(struct symtag)108 669.4 R F2(*)7.5 4.9 M F1
(lookup\(s\))-4.9 I(char)130.5 681.4 Q F2(*)7.5 4.9 M F1 1.5(s; {)-4.9 J
1.5(struct symtag)144 693.4 R F2(*)7.5 4.9 M F1(p;)-4.9 I 1.5
(for\( p=sym; p < &sym[nsym]; p)144 705.4 R F0(++)A F1(\))7.5 E 1.5
(if\( compar\(s, p)180 717.4 R F3(-)A F1 1.5(>id\) > 0\))B(return\(p\);)
216 729.4 Q EP
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/F0 10/Courier@0 SF 7.5(CT)72 36 S(utorial)-7.5 E/F1 10/Symbol SF(-)
153.51 E F0(20)7.5 E F1(-)7.5 E F0(return\(0\);)144 84 Q(})108 96 Q/F2
10/Times-Roman@0 SF(The function)72 113 Q F0(compar)2.5 E F2(doesn')2.5
E 2.5(tc)-.18 G(hange:)-2.5 E F0(`p)2.5 E F1(-)A F0(>id')A F2
(refers to a string.)2.5 E(In)97 128.6 Q F0(main)2.704 E F2 .204
(we test the pointer returned by)2.704 F F0(lookup)2.704 E F2(ag)2.704 E
.204(ainst zero, relying on the f)-.05 F .205(act that a pointer is by)
-.1 F(de\214nition ne)72 140.6 Q -.15(ve)-.25 G 2.5(rz).15 G
(ero when it really points at something.)-2.5 E
(The other pointer manipulations are tri)5 E(vial.)-.25 E
(The only comple)97 156.2 Q(xity is the set of lines lik)-.15 E(e)-.1 E
F0 1.5(struct symtag)108 173.2 R/F3 14/Courier@0 SF(*)7.5 4.9 M F0 1.5
(lookup\( \);)-4.9 J F2 .129(This brings us to an area that we will tre\
at only hurriedly _ the question of function types.)72 190.2 R .128
(So f)5.128 F(ar)-.1 E 2.628(,a)-.4 G .128(ll of our)-2.628 F .35
(functions ha)72 202.2 R .65 -.15(ve r)-.2 H .35(eturned inte).15 F .35
(gers \(or characters, which are much the same\).)-.15 F .351
(What do we do when the func-)5.351 F .088
(tion returns something else, lik)72 214.2 R 2.588(eap)-.1 G .087
(ointer to a structure?)-2.588 F .087(The rule is that an)5.087 F 2.587
(yf)-.15 G .087(unction that doesn')-2.587 F 2.587(tr)-.18 G .087
(eturn an)-2.587 F F0(int)72 226.2 Q F2 .493(has to say e)2.992 F .493
(xplicitly what it does return.)-.15 F .493
(The type information goes before the function name \(which)5.493 F
(can mak)72 238.2 Q 2.5(et)-.1 G(he name hard to see\).)-2.5 E
(Examples:)5 E F0 1.5(char f\(a\))108 255.2 R 1.5(int a; {)130.5 267.2 R
/F4 16/Courier@0 SF(...)144 279.2 Q F0(})108 291.2 Q(int)108 315.2 Q F3
(*)7.5 4.9 M F0 1.5(g\( \) {)-4.9 J F4(...)7.5 E F0(})7.5 E 1.5
(struct symtag)108 339.2 R F3(*)7.5 4.9 M F0 1.5(lookup\(s\) char)-4.9 J
F3(*)7.5 4.9 M F0 1.5(s; {)-4.9 J F4(...)7.5 E F0(})7.5 E F2 1.158
(The function)72 356.2 R F0(f)3.658 E F2 1.158(returns a character)3.658
F(,)-.4 E F0(g)3.658 E F2 1.157(returns a pointer to an inte)3.658 F
(ger)-.15 E 3.657(,a)-.4 G(nd)-3.657 E F0(lookup)3.657 E F2 1.157
(returns a pointer to a)3.657 F .702(structure that looks lik)72 368.2 R
(e)-.1 E F0(symtag)3.202 E F4(.)A F2 .702(And if we')5.702 F .703
(re going to use one of these functions, we ha)-.5 F 1.003 -.15(ve t)-.2
H 3.203(om).15 G(ak)-3.203 E 3.203(ea)-.1 G
(declaration where we use it, as we did in)72 380.2 Q F0(main)2.5 E F2
(abo)2.5 E -.15(ve)-.15 G(.).15 E
(Notice th parallelism between the declarations)97 395.8 Q F0 1.5
(struct symtag)144 412.8 R F3(*)7.5 4.9 M F0 1.5(lookup\( \);)-4.9 J 1.5
(struct symtag)144 424.8 R F3(*)7.5 4.9 M F0(psym;)-4.9 I F2 .767(In ef)
72 441.8 R .767(fect, this says that)-.25 F F0(lookup\( \))3.266 E F2
(and)3.266 E F0(psym)3.266 E F2 .766(are both used the same w)3.266 F
.766(ay _ as a pointer to a strcture _)-.1 F -2.15 -.25(ev e)72 453.8 T
2.5(nt).25 G(hough one is a v)-2.5 E
(ariable and the other is a function.)-.25 E/F5 10/Times-Bold@0 SF 2.5
(21. Initialization)72 477.8 R(of V)2.5 E(ariables)-.92 E F2 .079(An e)
97 493.4 R .079(xternal v)-.15 F .079
(ariable may be initialized at compile time by follo)-.25 F .08
(wing its name with an initializing v)-.25 F(al-)-.25 E .911
(ue when it is de\214ned.)72 505.4 R .911(The initializing v)5.911 F
.911(alue has to be something whose v)-.25 F .91(alue is kno)-.25 F .91
(wn at compile time,)-.25 F(lik)72 517.4 Q 2.5(eac)-.1 G(onstant.)-2.5 E
F0 12(int x)108 534.4 R 18(0; /)30 F F3(*)4.9 I F0 1.5
("0" could be any constant)7.5 -4.9 N F3(*)7.5 4.9 M F0(/)-4.9 I 12
(int a)108 546.4 R F1<a2>30 E F0(a)A F1<a2>A F0(;)A 6(char flag 0177;)
108 558.4 R(int)108 570.4 Q F3(*)18 4.9 M F0 21.6(p&)-4.9 K 30(y[1]; /)
-21.6 F F3(*)4.9 I F0 7.5(pn)7.5 -4.9 O 1.5(ow points to y[1])-7.5 F F3
(*)7.5 4.9 M F0(/)-4.9 I F2(An e)72 587.4 Q
(xternal array can be initialized by follo)-.15 E
(wing its name with a list of initializations enclosed in braces:)-.25 E
F0 12(int x[4])108 604.4 R 42({0,1,2,3}; /)12 F F3(*)4.9 I F0 1.5
(makes x[i] = i)7.5 -4.9 N F3(*)7.5 4.9 M F0(/)-4.9 I 12(int y[)108
616.4 R 10.5(]{)7.5 G 42(0,1,2,3}; /)-10.5 F F3(*)4.9 I F0 1.5
(makes y big enough for 4 values)7.5 -4.9 N F3(*)7.5 4.9 M F0(/)-4.9 I
(char)108 628.4 Q F3(*)12 4.9 M F0 3.6(msg "syntax)-4.9 J -1.5
(error\\n"; /)7.5 F F3(*)4.9 I F0 1.5(braces unnecessary here)7.5 -4.9 N
F3(*)7.5 4.9 M F0(/)-4.9 I(char)108 640.4 Q F3(*)7.5 4.9 M F0 1.5
(keyword[ ]{)-4.9 J("if",)144 652.4 Q("else",)144 664.4 Q("for",)144
676.4 Q("while",)144 688.4 Q("break",)144 700.4 Q("continue",)144 712.4
Q(0)144 724.4 Q EP
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/F0 10/Courier@0 SF 7.5(CT)72 36 S(utorial)-7.5 E/F1 10/Symbol SF(-)
153.51 E F0(21)7.5 E F1(-)7.5 E F0(};)108 84 Q/F2 10/Times-Roman@0 SF
.174(This last one is v)72 101 R .174(ery useful _ it mak)-.15 F(es)-.1
E F0(keyword)2.674 E F2 .175
(an array of pointers to character strings, with a zero at the)2.674 F
.079(end so we can identify the last element easily)72 113 R 5.079(.A)
-.65 G .078
(simple lookup routine could scan this until it either \214nds a)-2.5 F
(match or encounters a zero k)72 125 Q -.15(ey)-.1 G -.1(wo).15 G
(rd pointer:).1 E F0 36(lookup\(str\) /)108 142 R/F3 14/Courier@0 SF(*)
4.9 I F0 1.5(search for str in keyword[ ])7.5 -4.9 N F3(*)7.5 4.9 M F0
(/)-4.9 I(char)130.5 154 Q F3(*)7.5 4.9 M F0 1.5(str; {)-4.9 J 1.5
(int i,j,r;)144 166 R 1.5(for\( i=0; keyword[i] != 0; i)144 178 R F2(++)
A F0 7.5(\){)C 1.5(for\( j=0; \(r=keyword[i][j]\))180 190 R F2(==)7.5 E
F0 1.5(str[j] && r !=)7.5 F F1<a2>7.5 E F0(\\0)A F1<a2>A F0 7.5(;j)C F2
(++)-7.5 E F0(\);)7.5 E 1.5(if\( r)180 202 R F2(==)7.5 E F0 1.5
(str[j] \))7.5 F(return\(i\);)216 214 Q(})144 226 Q(return\()144 238 Q
F1(-)A F0(1\);)A(})108 250 Q F2(Sorry _ neither local v)97 270.6 Q
(ariables nor structures can be initialized.)-.25 E/F4 10/Times-Bold@0
SF 2.5(22. Scope)72 294.6 R(Rules: Who Kno)2.5 E(ws About What)-.1 E F2
2.841(Ac)97 310.2 S .341
(omplete C program need not be compiled all at once; the source te)
-2.841 F .342(xt of the program may be k)-.15 F(ept)-.1 E .933(in se)72
322.2 R -.15(ve)-.25 G .933(ral \214les, and pre).15 F .933
(viously compiled routines may be loaded from libraries.)-.25 F(Ho)5.932
E 3.432(wd)-.25 G 3.432(ow)-3.432 G 3.432(ea)-3.432 G .932(rrange that)
-3.432 F 1(data gets passed from one routine to another?)72 334.2 R
2.601 -.8(We h)6.001 H -2.25 -.2(av e).8 H 1.001(already seen ho)3.701 F
3.501(wt)-.25 G 3.501(ou)-3.501 G 1.001(se function ar)-3.501 F 1.001
(guments and)-.18 F -.25(va)72 346.2 S .446
(lues, so let us talk about e).25 F .446(xternal data.)-.15 F -.8(Wa)
5.446 G .446(rning: the w).8 F(ords)-.1 E/F5 10/Times-Italic@0 SF
(declar)2.945 E(ation)-.15 E F2(and)2.945 E F5(de\214nition)2.945 E F2
.445(are used precisely)2.945 F(in this section; don')72 358.2 Q 2.5(tt)
-.18 G(reat them as the same thing.)-2.5 E 3.024(Am)97 373.8 S .524
(ajor shortcut e)-3.024 F .524(xists for making)-.15 F F0(extern)3.024 E
F2 3.024(declarations. If)3.024 F .524(the de\214nition of a v)3.024 F
.524(ariable appears)-.25 F F5(be-)3.024 E(for)72 385.8 Q(e)-.37 E F2
(its use in some function, no)2.5 E F0(extern)2.5 E F2
(declaration is needed within the function.)2.5 E
(Thus, if a \214le contains)5 E F0 1.5(f1\( \) {)108 402.8 R/F6 16
/Courier@0 SF(...)7.5 E F0(})7.5 E 1.5(int foo;)108 419.8 R 1.5
(f2\( \) {)108 436.8 R F6(...)7.5 E F0 1.5(foo = 1;)7.5 F F6(...)7.5 E
F0(})7.5 E 1.5(f3\( \) {)108 453.8 R F6(...)7.5 E F0 1.5(if \( foo \))
7.5 F F6(...)7.5 E F0(})7.5 E F2 .402(no declaration of)72 470.8 R F0
(foo)2.902 E F2 .402(is needed in either)2.902 F F0(f2)2.902 E F2 .402
(or or)2.902 F F0(f3,)2.902 E F2 .401(because the e)2.901 F .401
(xternal de\214nition of)-.15 F F0(foo)2.901 E F2 .401(appears be-)2.901
F(fore them.)72 482.8 Q(But if)5 E F0(f1)2.5 E F2 -.1(wa)2.5 G
(nts to use).1 E F0(foo,)2.5 E F2(it has to contain the declaration)2.5
E F0 1.5(f1\( \) {)108 499.8 R 1.5(extern int foo;)144 511.8 R F6(...)
144 523.8 Q F0(})108 535.8 Q F2 .281(This is true also of an)97 556.4 R
2.782(yf)-.15 G .282(unction that e)-2.782 F .282
(xists on another \214le _ if it w)-.15 F(ants)-.1 E F0(foo)2.782 E F2
.282(it has to use an)2.782 F F0(extern)2.782 E F2 .227
(declaration for it.)72 568.4 R .227(\(If some)5.227 F .227
(where there is an)-.25 F F0(extern)2.727 E F2 .226
(declaration for something, there must also e)2.727 F -.15(ve)-.25 G
(ntually).15 E(be an e)72 580.4 Q(xternal de\214nition of it, or you')
-.15 E(ll get an `)-.1 E(`unde\214ned symbol')-.74 E 2.5('m)-.74 G
(essage.\))-2.5 E .005(There are some hidden pitf)97 596 R .005
(alls in e)-.1 F .006(xternal declarations and de\214nitions if you use\
 multiple source \214les.)-.15 F 1.6 -.8(To a)72 608 T -.2(vo).6 G
(id them, \214rst, de\214ne and initialize each e).2 E(xternal v)-.15 E
(ariable only once in the entire set of \214les:)-.25 E F0 12
(int foo 0;)108 625 R F2 -1.1(Yo)72 642 S 3.733(uc)1.1 G 1.233(an get a)
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(xternal de\214nitions on)-.15 F/F7 8/Times-Roman@0 SF(UNIX,)3.733 E F2
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1.233(so don')3.733 F 3.733(ta)-.18 G 1.232(sk for trouble.)-3.733 F
.547(Multiple initializations are ille)72 654 R -.05(ga)-.15 G 3.048(le)
.05 G -.15(ve)-3.298 G 3.048(rywhere. Second,).15 F .548(at the be)3.048
F .548(ginning of an)-.15 F 3.048<798c>-.15 G .548
(le that contains functions)-3.048 F 1.278(needing a v)72 666 R 1.278
(ariable whose de\214nition is in some other \214le, put in an)-.25 F F0
(extern)3.777 E F2 1.277(declaration, outside of an)3.777 F(y)-.15 E
(function:)72 678 Q F0 30(extern int)108 695 R(foo;)18 E 1.5(f1\( \) {)
108 712 R F6(...)7.5 E F0(})7.5 E(etc)130.5 724 Q F6(.)A EP
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/F0 10/Courier@0 SF 7.5(CT)72 36 S(utorial)-7.5 E/F1 10/Symbol SF(-)
153.51 E F0(22)7.5 E F1(-)7.5 E/F2 10/Times-Roman@0 SF(The)97 92.6 Q F0
(#include)2.682 E F2 .182
(compiler control line, to be discussed shortly)2.682 F 2.682(,l)-.65 G
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(yo)-.1 G 2.683(ft)-2.683 G .183(he e)-2.683 F(x-)-.15 E(ternal declara\
tions for a program and then stick them into each of the source \214les\
 making up the program.)72 104.6 Q/F3 10/Times-Bold@0 SF 2.5
(23. #de\214ne,)72 128.6 R(#include)2.5 E F2 2.5(Cp)97 144.2 S(ro)-2.5 E
(vides a v)-.15 E(ery limited macro f)-.15 E(acility)-.1 E 5(.Y)-.65 G
(ou can say)-6.1 E F0 24(#define name)108 161.2 R(something)48 E F2 .479
(and thereafter an)72 178.2 R .479(ywhere `)-.15 F(`name')-.74 E 2.979
('a)-.74 G .479(ppears as a tok)-2.979 F .479(en, `)-.1 F(`something')
-.74 E 2.978('w)-.74 G .478(ill be substituted.)-2.978 F .478
(This is particularly)5.478 F
(useful in parametering the sizes of arrays:)72 190.2 Q F0 24
(#define ARRAYSIZE)108 207.2 R(100)18 E 12(int arr[ARRAYSIZE];)144 219.2
R/F4 16/Courier@0 SF(...)151.5 231.2 Q F0 1.5(while\( i)144 243.2 R F2
(++)A F0 7.5(<A)7.5 G 1.5(RRAYSIZE \))-7.5 F F4(...)A F2(\(no)72 260.2 Q
2.599(ww)-.25 G 2.599(ec)-2.599 G .099
(an alter the entire program by changing only the)-2.599 F F0(define\))
2.6 E F2 .1(or in setting up mysterious constants:)2.6 F F0 24
(#define SET)108 277.2 R(01)54 E 24(#define INTERRUPT)108 289.2 R 18
(02 /)18 F/F5 14/Courier@0 SF(*)4.9 I F0 1.5(interrupt bit)7.5 -4.9 N F5
(*)7.5 4.9 M F0(/)-4.9 I 24(#define ENABLED 04)108 301.2 R F4(...)120
313.2 Q F0 1.5(if\( x & \(SET | INTERRUPT | ENABLED\) \))108 325.2 R F4
(...)7.5 E F2(No)72 342.2 Q 3.633(ww)-.25 G 3.633(eh)-3.633 G -2.25 -.2
(av e)-3.633 H 1.133(meaningful w)3.833 F 1.132
(ords instead of mysterious constants.)-.1 F 1.132
(\(The mysterious operators `&' \(AND\))6.132 F .4 LW 93.964 347.45
93.964 354.2 DL .694(and `)72 354.2 R 3.194('\()2 G .694
(OR\) will be co)-3.194 F -.15(ve)-.15 G .694(red in the ne).15 F .694
(xt section.\))-.15 F(It')5.694 E 3.195(sa)-.55 G 3.195(ne)-3.195 G .695
(xcellent practice to write programs without an)-3.345 F(y)-.15 E
(literal constants e)72 366.2 Q(xcept in)-.15 E F0(#define)2.5 E F2
(statements.)2.5 E 1.594(There are se)97 381.8 R -.15(ve)-.25 G 1.594
(ral w).15 F 1.594(arnings about)-.1 F F0(#define)4.094 E F4(.)A F2
1.594(First, there')6.594 F 4.094(sn)-.55 G 4.094(os)-4.094 G 1.594
(emicolon at the end of a)-4.094 F F0(#de-)4.094 E(fine;)72 393.8 Q F2
.748(all the te)3.248 F .748
(xt from the name to the end of the line \(e)-.15 F .748
(xcept for comments\) is tak)-.15 F .748(en to be the `)-.1 F(`some-)
-.74 E(thing')72 405.8 Q 2.543('. When)-.74 F(it')2.543 E 2.543(sp)-.55
G .043(ut into the te)-2.543 F .043(xt, blanks are placed around it.)
-.15 F .042(Good style typically mak)5.043 F .042(es the name in the)-.1
F F0(#define)72 417.8 Q F2 .176(upper case _ this mak)2.676 F .176
(es parameters more visible.)-.1 F .176(De\214nitions af)5.176 F .176
(fect things only after the)-.25 F 2.676(yo)-.15 G(ccur)-2.676 E(,)-.4 E
.19(and only within the \214le in which the)72 429.8 R 2.69(yo)-.15 G
(ccur)-2.69 E 5.19(.D)-.55 G .19(e\214nes can')-5.19 F 2.69(tb)-.18 G
2.69(en)-2.69 G 2.69(ested. Last,)-2.69 F .19(if there is a)2.69 F F0
(#define)2.69 E F2 .19(in a \214le,)2.69 F
(then the \214rst character of the \214le)72 441.8 Q/F6 10
/Times-Italic@0 SF(must)2.5 E F2
(be a `#', to signal the preprocessor that de\214nitions e)2.5 E(xist.)
-.15 E .557(The other control w)97 469.4 R .557(ord kno)-.1 F .557
(wn to C is)-.25 F F0(#include)3.058 E F4(.)A F2 2.158 -.8(To i)5.558 H
.558(nclude one \214le in your source at compila-).8 F(tion time, say)72
481.4 Q F0 1.5(#include "filename")108 498.4 R F2 .114
(This is useful for putting a lot of hea)72 515.4 R .113
(vily used data de\214nitions and)-.2 F F0(#define)2.613 E F2 .113
(statements at the be)2.613 F .113(ginning of)-.15 F 2.725<618c>72 527.4
S .225(le to be compiled.)-2.725 F .225(As with)5.225 F F0(#define,)
2.725 E F2 .225(the \214rst line of a \214le containing a)2.725 F F0
(#include)2.725 E F2 .225(has to be)2.725 F .225(gin with)-.15 F 2.5(a`)
72 539.4 S 2.5(#'. And)-2.5 F F0(#include)2.5 E F2(can')2.5 E 2.5(tb)
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G(ontain another)-2.5 E F0(#include)2.5 E F4(.)A F3 2.5(24. Bit)72 563.4
R(Operators)2.5 E F2 2.5(Ch)97 579 S(as se)-2.5 E -.15(ve)-.25 G
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G(xample,)-2.65 E F0 7.5(x=x&0)108 596 S(177;)-7.5 E F2 .326
(forms the bit-wise)72 613 R/F7 8/Times-Roman@0 SF(AND)2.825 E F2(of)
2.825 E F0(x)2.825 E F2 .325(and 0177, ef)2.825 F(fecti)-.25 E -.15(ve)
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.15 G .325(its of)-2.825 F F0(x)2.825 E F4(.)A F2 .325(Other operators)
5.325 F(are)72 625 Q 109 635.25 109 642 DL(inclusi)144 642 Q .925 -.15
(ve O)-.25 H(R).15 E 32.67(^\()108 654 S(circumfle)-32.67 E .625(x\) e)
-.15 F(xclusi)-.15 E .925 -.15(ve O)-.25 H(R).15 E 32.67(~\()108 666 S
.625(tilde\) 1)-32.67 F F1<a2>A F2 3.125(sc)C(omplement)-3.125 E 32.67
(!l)108 678 S .625(ogical NO)-32.67 F(T)-.4 E 22.22(<< left)108 690 R
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/F0 10/Times-Roman@0 SF 2.5(CT)72 36 S 179.73(utorial -)-2.95 F(23 -)2.5
E/F1 10/Times-Bold@0 SF 2.5(25. Assignment)72 84 R(Operators)2.5 E F0
.521(An unusual feature of C is that the normal binary operators lik)97
99.6 R 3.021(e`)-.1 G .521(+', `)-3.021 F/F2 10/Symbol SF(-)A F0 .521
(', etc.)B .522(can be combined with)5.521 F
(the assignment operator `=' to form ne)72 111.6 Q 2.5(wa)-.25 G
(ssignment operators.)-2.5 E -.15(Fo)5 G 2.5(re).15 G(xample,)-2.65 E/F3
10/Courier@0 SF 7.5(x=)108 128.6 S F2(-)-7.5 E F3(10;)7.5 E F0
(uses the assignment operator `=)72 145.6 Q F2(-)A F0 2.5('t)C 2.5(od)
-2.5 G(ecrement)-2.5 E F3(x)2.5 E F0(by 10, and)2.5 E F3 7.5(x=)108
162.6 S 7.5(&0)-7.5 G(177)-7.5 E F0 .289(forms the)72 179.6 R/F4 8
/Times-Roman@0 SF(AND)2.789 E F0(of)2.789 E F3(x)2.789 E F0 .289
(and 0177.)2.789 F .289(This con)5.289 F -.15(ve)-.4 G .288
(ntion is a useful notational shortcut, particularly if).15 F F3(x)2.788
E F0 .288(is a compli-)2.788 F(cated e)72 191.6 Q 2.5(xpression. The)
-.15 F(classic e)2.5 E(xample is summing an array:)-.15 E F3 1.5
(for\( sum=i=0; i<n; i)108 208.6 R F0(++)A F3(\))7.5 E 1.5
(sum =+ array[i];)144 220.6 R F0
(But the spaces around the operator are critical!)72 237.6 Q -.15(Fo)5 G
2.5(ri).15 G(nstance,)-2.5 E F3 7.5(x=)108 254.6 S F2(-)A F3(10;)A F0
(sets)72 271.6 Q F3(x)2.5 E F0(to)2.5 E F2(-)2.5 E F0(10, while)A F3 7.5
(x=)108 288.6 S F2(-)-7.5 E F3(10;)7.5 E F0(subtracts 10 from)72 305.6 Q
F3(x)2.5 E/F5 16/Courier@0 SF(.)A F0(When no space is present,)5 E F3
(x=)108 322.6 Q F2(-)A F3(10;)A F0 .265(also decreases)72 339.6 R F3(x)
2.765 E F0 .266(by 10.)2.766 F .266(This is quite contrary to the e)
5.266 F .266(xperience of most programmers.)-.15 F .266(In particular)
5.266 F 2.766(,w)-.4 G(atch)-2.866 E(out for things lik)72 351.6 Q(e)-.1
E F3(c=)108 368.6 Q/F6 14/Courier@0 SF(*)4.9 I F3(s)-4.9 I F0(++)A F3(;)
A(y=&x[0];)108 380.6 Q F0 .595
(both of which are almost certainly not what you w)72 397.6 R 3.094
(anted. Ne)-.1 F .594(wer v)-.25 F .594(ersions of v)-.15 F .594
(arious compilers are courte-)-.25 F(ous enough to w)72 409.6 Q
(arn you about the ambiguity)-.1 E(.)-.65 E .682
(Because all other operators in an e)97 425.2 R .682(xpression are e)
-.15 F -.25(va)-.25 G .682(luated before the assignment operator).25 F
3.183(,t)-.4 G .683(he order)-3.183 F(of e)72 437.2 Q -.25(va)-.25 G
(luation should be w).25 E(atched carefully:)-.1 E F3 7.5(x=x)108 454.2
S 1.5(<<y | z;)-7.5 F F0(means `)72 471.2 Q(`shift)-.74 E F3(x)2.5 E F0
(left)2.5 E F3(y)2.5 E F0(places, then)2.5 E F4(OR)2.5 E F0(with)2.5 E
F3(z,)2.5 E F0(and store in)2.5 E F3(x)2.5 E F5(.)A F3('')A F0(But)5 E
F3 7.5(x=)108 488.2 S 1.5(<< y | z;)-7.5 F F0(means `)72 505.2 Q(`shift)
-.74 E F3(x)2.5 E F0(left by)2.5 E F3(y|z)2.5 E F0(places')2.5 E
(', which is rather dif)-.74 E(ferent.)-.25 E F1 2.5(26. Floating)72
529.2 R -.2(Po)2.5 G(int).2 E F0 -.8(We)97 544.8 S -1.65 -.5('v e).8 H
.353(skipped o)3.353 F -.15(ve)-.15 G 2.853<728d>.15 G .353
(oating point so f)-2.853 F(ar)-.1 E 2.853(,a)-.4 G .353
(nd the treatment here will be hasty)-2.853 F 5.353(.C)-.65 G .352
(has single and dou-)-2.501 F(ble precision numbers \(where the precisi\
on depends on the machine at hand\).)72 556.8 Q -.15(Fo)5 G 2.5(re).15 G
(xample,)-2.65 E F3 1.5(double sum;)144 573.8 R 1.5(float avg, y[10];)
144 585.8 R 1.5(sum = 0)144 597.8 R F5(.)A F3(0;)A 1.5
(for\( i=0; i<n; i)144 609.8 R F0(++)A F3(\))7.5 E 1.5(sum =+ y[i];)180
621.8 R 1.5(avg = sum/n;)144 633.8 R F0(forms the sum and a)72 650.8 Q
-.15(ve)-.2 G(rage of the array).15 E F3(y)2.5 E F5(.)A F0 .621
(All \215oating arithmetic is done in double precision.)97 666.4 R(Mix)
5.621 E .621(ed mode arithmetic is le)-.15 F -.05(ga)-.15 G .622
(l; if an arithmetic).05 F 1.828(operator in an e)72 678.4 R 1.828
(xpression has both operands)-.15 F F3(int)4.328 E F0(or)4.328 E F3
(char,)4.328 E F0 1.827(the arithmetic done is inte)4.328 F(ger)-.15 E
4.327(,b)-.4 G 1.827(ut if one)-4.527 F .454(operand is)72 690.4 R F3
(int)2.954 E F0(or)2.954 E F3(char)2.954 E F0 .455(and the other is)
2.954 F F3(float)2.955 E F0(or)2.955 E F3(double,)2.955 E F0 .455
(both operands are con)2.955 F -.15(ve)-.4 G .455(rted to).15 F F3
(double)2.955 E F5(.)A F0(Thus if)72 702.4 Q F3(i)2.5 E F0(and)2.5 E F3
(j)2.5 E F0(are)2.5 E F3(int)2.5 E F0(and)2.5 E F3(x)2.5 E F0(is)2.5 E
F3(float,)2.5 E 60(\(x+i\)/j converts)108 719.4 R 7.5(ia)7.5 G 1.5
(nd j to float)-7.5 F 7.5(x+i)108 731.4 S 57(/j does)-7.5 F 1.5
(i/j integer, then converts)7.5 F EP
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/F0 10/Courier@0 SF 7.5(CT)72 36 S(utorial)-7.5 E/F1 10/Symbol SF(-)
153.51 E F0(24)7.5 E F1(-)7.5 E/F2 10/Times-Roman@0 SF -.8(Ty)72 89 S
(pe con).8 E -.15(ve)-.4 G
(rsion may be made by assignment; for instance,).15 E F0 1.5(int m, n;)
144 106 R 1.5(float x, y;)144 118 R 7.5(m=x)144 130 S(;)-7.5 E 7.5(y=n)
144 142 S(;)-7.5 E F2(con)72 159 Q -.15(ve)-.4 G(rts).15 E F0(x)2.5 E F2
(to inte)2.5 E(ger \(truncating to)-.15 E -.1(wa)-.25 G(rd zero\), and)
.1 E F0(n)2.5 E F2(to \215oating point.)2.5 E .545
(Floating constants are just lik)97 174.6 R 3.045(et)-.1 G .545
(hose in F)-3.045 F .545(ortran or PL/I, e)-.15 F .545(xcept that the e)
-.15 F .544(xponent letter is `e' instead)-.15 F(of `E'.)72 186.6 Q
(Thus:)5 E F0 1.5(pi = 3)144 203.6 R/F3 16/Courier@0 SF(.)A F0(14159;)A
1.5(large = 1)144 215.6 R F3(.)A F0(23456789e10;)A(printf)97 236.2 Q F2
.561(will format \215oating point numbers:)3.061 F F0(``%w)3.061 E F3(.)
A F0(df'')A F2 .562(in the format string will print the corre-)3.061 F
.353(sponding v)72 248.2 R .353(ariable in a \214eld)-.25 F F0(w)2.853 E
F2 .353(digits wide, with)2.853 F F0(d)2.853 E F2 .353(decimal places.)
2.853 F(An)5.353 E F0(e)2.853 E F2 .353(instead of an)2.853 F F0(f)2.853
E F2 .353(will produce e)2.853 F(xpo-)-.15 E(nential notation.)72 260.2
Q/F4 10/Times-Bold@0 SF 2.5(27. Horr)72 284.2 R(ors! goto')-.18 E 2.5
(sa)-.37 G(nd labels)-2.5 E F2 3.171(Ch)97 299.8 S .671(as a)-3.171 F F0
(goto)3.171 E F2 .671
(statement and labels, so you can branch about the w)3.171 F .671
(ay you used to.)-.1 F .671(But most of the)5.671 F(time)72 311.8 Q F0
(goto's)2.978 E F2(aren')2.978 E 2.978(tn)-.18 G 2.978(eeded. \(Ho)
-2.978 F 2.978(wm)-.25 G(an)-2.978 E 2.978(yh)-.15 G -2.25 -.2(av e)
-2.978 H .478(we used up to this point?\))3.178 F .477
(The code can almost al)5.478 F -.1(wa)-.1 G .477(ys be).1 F
(more clearly e)72 323.8 Q(xpressed by)-.15 E F0 -3.5
(for/while, if/else,)2.5 F F2(and compound statements.)2.5 E 1.615
(One use of)97 339.4 R F0(goto's)4.115 E F2 1.615(with some le)4.115 F
(gitimac)-.15 E 4.115(yi)-.15 G 4.115(si)-4.115 G 4.115(nap)-4.115 G
1.616(rogram which contains a long loop, where a)-4.115 F F0(while\(1\))
72 351.4 Q F2 -.1(wo)2.5 G(uld be too e).1 E 2.5(xtended. Then)-.15 F
(you might write)2.5 E F0(mainloop:)130.5 368.4 Q F3(...)144 380.4 Q F0
1.5(goto mainloop;)144 392.4 R F2 .524(Another use is to implement a)72
409.4 R F0(break)3.024 E F2 .524(out of more than one le)3.024 F -.15
(ve)-.25 G 3.024(lo).15 G(f)-3.024 E F0(for)3.023 E F2(or)3.023 E F0
(while)3.023 E F3(.)A F0(goto's)5.523 E F2 .523(can only)3.023 F
(branch to labels within the same function.)72 421.4 Q F4 2.5(28. Ackno)
72 445.4 R(wledgements)-.1 E F2 2.783(Ia)97 461 S 2.783(mi)-2.783 G .283
(ndebted to a v)-2.783 F .283(eritable host of readers who made v)-.15 F
.284(aluable criticisms on se)-.25 F -.15(ve)-.25 G .284
(ral drafts of this tu-).15 F 2.59(torial. The)72 473 R 2.59(yr)-.15 G
.09(anged in e)-2.59 F .09(xperience from complete be)-.15 F .09
(ginners through se)-.15 F -.15(ve)-.25 G .09
(ral implementors of C compilers to).15 F .287
(the C language designer himself.)72 485 R .288(Needless to say)5.288 F
2.788(,t)-.65 G .288
(his is a wide enough spectrum of opinion that no one is)-2.788 F .219(\
satis\214ed \(including me\); comments and suggestions are still welcom\
e, so that some future v)72 497 R .219(ersion might be)-.15 F(impro)72
509 Q -.15(ve)-.15 G(d.).15 E F0(References)72 605 Q F2 3.156(Ci)97
620.6 S 3.156(sa)-3.156 G 3.156(ne)-3.156 G .656(xtension of B, which w)
-3.306 F .656(as designed by D. M. Ritchie and K. L. Thompson [4].)-.1 F
.656(The C lan-)5.656 F .331(guage design and)72 632.6 R/F5 8
/Times-Roman@0 SF(UNIX)2.831 E F2 .331(implementation are the w)2.831 F
.331(ork of D. M. Ritchie.)-.1 F(The)5.331 E F5(GCOS)2.83 E F2 -.15(ve)
2.83 G .33(rsion w).15 F .33(as be)-.1 F .33(gun by A.)-.15 F(Sn)72
644.6 Q .819
(yder and B. A. Barres, and completed by S. C. Johnson and M. E. Lesk.)
-.15 F(The)5.819 E F5(IBM)3.319 E F2 -.15(ve)3.319 G .819
(rsion is primarily).15 F(due to T)72 656.6 Q 2.5(.G)-.74 G 2.5(.P)-2.5
G(eterson, with the assistance of M. E. Lesk.)-2.5 E 10.84([1] D.)72
672.2 R(M. Ritchie,)2.5 E/F6 10/Times-Italic@0 SF 2.5(CR)2.5 G(efer)-2.5
E(ence Manual.)-.37 E F2(Bell Labs, Jan. 1974.)5 E 10.84([2] M.)97 687.8
R(E. Lesk & B. A. Barres,)2.5 E F6(The GCOS C Libr)2.5 E(ary)-.15 E(.)
-.55 E F2(Bell Labs, Jan. 1974.)5 E EP
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/F0 10/Times-Roman@0 SF 2.5(CT)72 36 S 179.73(utorial -)-2.95 F(25 -)2.5
E 10.84([3] D.)122 84 R 1.139(M. Ritchie & K. Thompson,)3.639 F/F1 10
/Times-Italic@0 SF 1.138(UNIX Pr)3.638 F -.1(og)-.45 G -.15(ra).1 G
(mmer').15 E 3.638(sM)-.4 G(anual.)-3.638 E F0 1.138
(5th Edition, Bell Labs,)6.138 F(1974.)147 96 Q 10.84([4] S.)147 111.6 R
.177(C. Johnson & B. W)2.677 F 2.677(.K)-.92 G(ernighan,)-2.927 E F1
.178(The Pr)2.678 F -.1(og)-.45 G -.15(ra).1 G .178(mming Langua).15 F
.378 -.1(ge B)-.1 H(.).1 E F0 .178(Computer Sci-)5.178 F(ence T)172
123.6 Q(echnical Report 8, Bell Labs, 1972.)-.7 E EP
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