CS 11 C track: lecture 1

Transcription

1 CS 11 C track: lecture 1 Prelimiaries Need a CMS cluster accout Need to kow UNIX IMSS tutorial liked from track home page Track home page: /c/mike/idex.html

2 Assigmets 1st assigmet is posted ow Due oe week after class, midight Gradig system: see "admi page" liked from track home page

3 Other admiistrative stuff See admi web page: /admi.html Covers how to submit labs, collaboratio policy, gradig, etc.

4 Textbook Kerigha ad Ritchie: The C Programmig Laguage, 2d. ed. 1st editio NOT acceptable "ANSI C" Oly for referece

5 C: pros ad cos What C is good at low-level programmig speed ad memory efficiecy portability (sorta) Bad thigs about C usafe!!! low level of abstractio

6 Gettig started (1) The "hello, world!" program: #iclude <stdio.h> it mai(void) { pritf("hello, world!\"); retur 0;

7 Gettig started (2) Make this ito a file called hello.c usig a text editor e.g. emacs, vi, edit, pico Compile ito a program ad ru: % gcc hello.c -o hello %./hello hello, world! % Woo hoo!

8 Source code to executable (1) What you write is called "source code" Two kids of source code files: regular code (files ed i ".c") header files (files ed i ".h") Compiler turs source code ito "object code" (files ed i ".o") Liker turs object code file(s) ito executable (o special file suffix)

9 Source code to executable (2) The program gcc is both a compiler ad a liker Whe you do this: % gcc hello.c -o hello The gcc compiles hello.c to hello.o liks hello.o with system libraries outputs the biary executable program hello removes hello.o

10 Source code to executable (3) You ca do each step idividually: % gcc -c hello.c (compile oly) % gcc hello.o -o hello (lik oly) I this case, hello.o is ot removed Sequece: compilig: source code to object code likig: object code to biary executable

11 The C laguage - overview Programs are built up of fuctios Fuctios take i argumets compute somethig retur a result The mai() fuctio is where program executio starts

12 Data types (1) All data i C has to have a specified type Examples: it (iteger) char (character) float or double (approximate real umber) others Variables hold data of a particular type oly Variables must be declared before use

13 Data types (2) Type declaratios: it i; /* ame = i type = it */ char c; /* ame = c type = char */ double d; float some_float = 3.14; Idetifiers: i, c, d, some_float Optioal iitializatio (e.g. some_float) Booleas à 0 or ozero (usually 1)

14 Data types (3) Strigs: arrays of type char char some_strig[9] = "woo hoo!"; char same_strig[] = "woo hoo!"; Much more o strigs, arrays later Other types: structs, poiters

15 Operators (1) Numeric: + - * / % Assigmet: = it i = 10; /* iitializatio */ it j = 20; /* iitializatio */ i = 2 + i * j; /* assigmet */ j = j % 2; /* assigmet */

16 Assigmet operator Assigmet works this way: 1) Evaluate the right-had side (RHS) of the assigmet operator 2) Assig the resultig value to the left-had side (LHS) of the assigmet operator

17 Operators (2) What does i = 2 + i * j; mea? a) i = (2 + i) * j; b) i = 2 + (i * j); * has a higher precedece tha + Use () to force other iterpretatio

18 Operators (3) Other assigmet operators: +=, -=, *=,... i += 2; /* i = i + 2; */ icremet ad decremet: ++, -- i++; /* i = i + 1; */ ++i; /* same */

19 Operators (4) Test operators: compare two values < <= > >= == for testig equality!= for testig iequality read "!" as "ot"

20 Operators (5) Logical operators: argumets are its used as booleas i.e. usually 0 or 1 (false or true)! operator is uary logical "ot" && operator is biary logical "ad" operator is biary logical "or"

21 Operators (6) it bool1, bool2, bool3, bool4; bool1 = 0; /* false */ bool2 =!bool1; /* bool2 --> true */ bool3 = bool1 bool2; /* value? */ bool4 = bool1 && bool2; /* value? */

22 Operators (7) "Uary mius" operator: it var1 = 10; it var2; var2 = -var1; Like with othig to the left Negates the value

23 Expressios ad statemets i + 2 * j is a expressio (has a value) i = j * k; is a statemet eds i a semicolo also is a expressio (value is value of i) i = j = k = 0; is allowed Equivalet to i = (j = (k = 0)); NOT ((i = j) = k) = 0;

24 Commets /* This is a commet. */ /* * Commets ca spa * multiple lies. */ // This is NOT a commet!

25 Fuctios (1) Fuctios take argumets ad retur values: it f(it x) { it y = 10; retur y * x;

26 Fuctios (2) Fuctios take argumets ad retur values: it f(it x) { it y = 10; retur y * x; ame

27 Fuctios (3) Fuctios take argumets ad retur values: it f(it x) { it y = 10; retur y * x; argumet list

28 Fuctios (4) Fuctios take argumets ad retur values: it f(it x) { it y = 10; retur y * x; retur type

29 Fuctios (5) Fuctios take argumets ad retur values: it f(it x) { it y = 10; retur y * x; body

30 Fuctios (6) Fuctios take argumets ad retur values: it f(it x) { it y = 10; retur y * x; retur statemet

31 Fuctios (7) Callig the fuctio we just defied: /* i aother fuctio... */ it res; it i = 10; res = f(10); res = f(5 + 5); res = f(i); res = f(i*5 + i/2); All of these are valid fuctio calls Take i argumets, retur result

32 Fuctios (8) Fuctios ca take multiple argumets: it g(it x, it y) { it z = 42; retur x * y * z; argumet list Argumet ames (x, y) preceded by types (it) Argumets separated by commas

33 Fuctios (9) Callig fuctios that take multiple argumets: /* i aother fuctio... */ it res; it i = 10, j = 20; res = g(10, 20); res = g(5 + 5, 20); res = g(i, j); res = g(i*5 + i/2, j * 10);

34 Fuctios (10) Not all fuctios retur values: void prit_umber(it i) { pritf("umber is: %d\", i); Retur type is void (othig to retur) Use this whe o retur value eeded

35 Fuctios (11) Not all fuctios retur values: void prit_umber(it i) { pritf("umber is: %d\", i); retur; /* uecessary */ retur statemet ot required uless you retur i the middle of the fuctio

36 Fuctios (12) Callig this fuctio: /* I aother fuctio... */ it i = 10; prit_umber(20); prit_umber(i); prit_umber(i*5 + i/2); Prits 20, 10, 55 respectively

37 Fuctios (13) Not all fuctios take argumets: it five(void) { retur 5; No argumets (use void to idicate)

38 Fuctios (14) Callig fuctios without argumets: it value; value = five(); Now value equals 5 Note () after five meas "this fuctio is beig called with o argumets" Without this, fuctio wo't be called!

39 Fuctios type declaratios Type declaratios come at the begiig of the fuctio Need a declaratio for every local variable it foo(it x) { it y; /* type declaratio */ y = x * 2; retur y;

40 Fuctios type declaratios This is wrog: it foo(it x) { it y; /* type decl */ y = x * 2; /* code */ /* type declaratio after code: */ it z = y * y; retur z; Geerates a compiler warig

41 Local ad global variables (1) Variable declaratios ca be local or global Local: iside a fuctio Global: outside a fuctio accessible from ay fuctio

42 Local ad global variables (2) it x; /* Global variable */ it y = 10; /* Iitialized global variable */ it foo(it z) { it w; /* local variable */ x = 42; /* assig to a global variable */ w = 10; /* assig to a local variable */ retur (x + y + z + w);

43 Local ad global variables (3) I geeral, avoid usig global variables! Global variables ca be chaged by ay fuctio makes debuggig much harder Global variables are ever ecessary though sometimes coveiet OK to use global "variables" if they really are costat i.e. if you do't chage their values

44 pritf() it a = 5; double pi = ; char s[] = "I am a strig!"; pritf("a = %d, pi = %f, s = %s\", a, pi, s); Substitutes values for %d, %f, %s etc. %d : it, %f : float, double, %s : strig \ : ew lie

45 The C preprocessor (1) What does the fuky lie #iclude <stdio.h> mea? C preprocessor directive Extra step i compilatio: cpp: source code -> expaded source code gcc: compiles source code -> object code gcc (ld): liks object code -> executable gcc does all this for you

46 The C preprocessor (2) What does the fuky lie #iclude <stdio.h> mea? Icludes the declaratio of pritf() NOT the implemetatio allows your code to use pritf() The liker adds i the implemetatio

47 Coditioals (1) Need to be able to test for coditios: it a = 10; if (a < 20) { pritf("less tha 20\"); else { pritf("ot less tha 20\");

48 Coditioals (2) Test: 0 is "false", aythig else is "true": if (1) /* true */ { pritf("less tha 20\"); else { pritf("ot less tha 20\");

49 Coditioals (3) VERY commo error: it a = 0; if (a = 10) /* always true! */ { pritf("a equals 10\"); else { pritf("a does t equal 10\");

50 Coditioals (4) Should be: it a = 0; if (a == 10) /* ot always true */ { pritf("a equals 10\"); else { pritf("a does t equal 10\");

51 Coditioals (5) else clause is optioal: it a = 0; if (a == 10) { pritf("a equals 10\");

52 Coditioals (5) else if for multiple cases: it a = 0; if (a == 10) { pritf("a equals 10\"); else if (a < 10) { pritf("a is less tha 10\"); else { pritf("a is greater tha 10\");

53 for loop (1) Need to do thigs repeatedly: it i; for (i = 0; i < 10; i++) { pritf("cowabuga!!!\");

54 for loop (2) for (<iitializatio>; <test>; <icremet>) { <body> for (i = 0; i < 10; i++) { pritf("cowabuga!!!\");

55 for loop (3) for (<iitializatio>; <test>; <icremet>) { <body> for (i = 0; i < 10; i++) { pritf("cowabuga!!!\");

56 for loop (4) for (<iitializatio>; <test>; <icremet>) { <body> for (i = 0; i < 10; i++) { pritf("cowabuga!!!\");

57 for loop (5) for (<iitializatio>; <test>; <icremet>) { <body> for (i = 0; i < 10; i++) { pritf("cowabuga!!!\");

58 for loop (6) for (<iitializatio>; <test>; <icremet>) { <body> for (i = 0; i < 10; i++) { pritf("cowabuga!!!\");

59 That's all for ow! Much more o all these topics i later lectures Do first assigmet to get familiar with basics Use "style checker" to avoid style mistakes Have fu!