1 int factorial (int n) { int i, - - PDF document

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int factorial (int n) { int i, product = 1; for (i = 2; i <= n; ++i) product *= i; return product; }

int

int

factorial(7)

void wrt_adress(void) { printf(”%s\n%s\n%s\n%s\n\n”, ” **********************”, ” ** SANTA CLAUS **”, ” ** NORTH POLE **”, ” **********************”); }

wrt_adress()

for (i = 0; i < 3; i++) wrt_adress();

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void nothing(void) { } /* does nothing */ double twice(double x) { return (2.0 * x); } int all_add(int a, int b) { int c; ..... return (a + b + c); }

#include <stdio.h> int a = 33; int main(void) { int b = 77; printf(”%d\n”, a + b); }

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return; return ++a; return (a * b);

return

return

double sqrt(double);

• ❋✑❍✢❉✁■✎❂✒❃✰❉✙❉✘❃✰❄✑❏✤■❆■✎❂✞❑☞❇✑❍✒❃✰❄✑❉▲■✶▼✸❉✁◆✎❖✖❃✰❄ double

double

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void f(char c, int i);

void f(char, int);

c

sqrt()

sqrt(4)

f(x)

int f();

extern

static

extern

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#include

#include <stdio.h> #define N 7 void prn_heading(void) { .... } void power(int m, int n) { .... } int main(void) { prn_heading(); printf(”%d\n”, power(7,3)); }

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• ❍✽✿❀❃●❍❀■❂❋❂❏✼✾❑✖✸✺✹✖▲▼❂❋❊

#include <stdio.h> int compute_sum(int n); int main(void) { int n = 3, sum; printf(”%d\n”, n); sum = compute_sum(n); printf(”%d\n”, n); printf(”%d\n”, sum); } /* forts. nästa slide */

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/* forts. från förra slide */ int compute_sum(int n) { int sum = 0; for (; n > 0; --n) sum += n; return sum; }

return

• ✝❍

return

return

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• ✄✝✆✘ù

#include ”pgm.h”

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#include <stdio.h> #include <stdlib.h> #define N 3 /* funktionsprototyper */ void fct1(int k); void fct2(void); void wrt_info(char *);

#include ”pgm.h” int main(void) { char ans; int i, n = N; printf(”%s”, ”This program does not do very much.\n” ”Do you want more information? ”); scanf(”%c”, &ans); if (ans == ’y’ || ans == ’Y’) wrt_info(”pgm”); for (i=0; i < n; ++i) fct1(i); printf(”Bye!\n”); return 0; }

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#include ”pgm.h” void fct1(int n) { int i; printf(”Hello from fct1()\n”); for (i=0; i < n; ++i) fct2(); } void fct2(void) { printf(”Hello from fct2()\n”); }

#include ”pgm.h” void mrt_info(char *pgm_name) { printf(”Usage: %s\n\n”, pgm_name); printf(”%s\n”, ”This program illustrates how one can write a program\n” ”in more than one file. In this example, we have a\n” ”single .h file that gets included at the top of our\n” ”three .c files. Thus, the .h file acts as the \”glue\”\n” ”that binds the program together.\n\n” ”Note that the functions fct1() and fct2() when called\n” ”first says \”hello\”. When writing a serious program, the\n” ”programmer sometimes does this in a first working version\n” ”the code.\n”); } /* } on this line to save space only! */

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• ✡❑▼▲❖◆✞P✡❑❄◗✯❘ assert()

#include <assert.h> int f(int a, int b) { assert(a!=4 && b!=0); return a/b; } int main() { f(2, 0); /* assertion will fail! */ }

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”Assertion failed on line 23”

assert()

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{ int a = 2; /* outer block a */ printf(”%d\n”, a); { int a = 5; /* inner block a */ printf(”%d\n”, a); } printf(”%d\n”, ++a); /* back to the outer block a */ }

{ int a = 1, b = 2, c = 3; printf(”%3d%3d%3d\n”, a, b, c); { int b = 4; float c = 5.0; printf(”%3d%3d%5.1f\n”, a, b, c); a = b; { int c; c = b; printf(”%3d%3d%3d\n”, a, b, c); } printf(”%3d%3d%5.1f\n”, a, b, c); } printf(”%3d%3d%3d\n”, a, b, c); }

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{ int a, b; { /* inner block 1 */ float b; ... /* int a is known, but not int b */ } { /* inner block 2 */ float a; ... /* int b is known but not int a.*/ /* nothing in inner block 1 is known */ } }

v

{ static int cnt = 0; printf(”*** debug: cnt = %d v = %d\n”, ++cnt, v); }

• cnt

static

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static

auto

auto

auto int a, b, c; auto float f;

• ù auto

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• ✴❁✽❍❅❊✍■✰❊✗✹❇✼❉✵✤❋

extern

#include <stdio.h> int a = 1, b = 2, c = 3; int f(void); int main(void) { printf(”%3d\n”, f()); printf(”%3d%3d%3d\n”, a, b, c); return 0; } int f(void) { int b, c; a = b = c = 4; return (a + b + c); }

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extern

auto

register

• extern

#include <stdio.h> int a = 1, b = 2, c = 3; int f(void); int main(void) { printf(”%3d\n”, f()); printf(”%3d%3d%3d\n”, a, b, c); return 0; }

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int f(void) { extern int a; /* look for it elsewhere */ int b, c; a = b = c = 4; return (a + b + c); }

register

register

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{ register int i; for (i = 0; i < LIMIT; ++i) { ... } } /* block exit will free register */

int

register i; ⑨✯⑩✤❶❯❷✯❸✣❸✤❷P❶❯❷✽❹✣❶❘❺❊❸ register int i;

void f(void) { static int cnt = 0; ++cnt; if (cnt % 2 == 0) .... /* do something */ else .... /* do something different */ }

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static

#define INITIAL_SEED 17 #define MULTIPLIER 25173 #define INCREMENT 13849 #define MODULUS 65536 #define FLOATING_MODULUS 65536.0 static unsigned seed = INITIAL_SEED; /* external but private for this file */ unsigned random(void) { seed = (MULTIPLIER * seed + INCREMENT) % MODULUS; return seed; } double probability(void) { seed = (MULTIPLIER * seed + INCREMENT) % MODULUS; return (seed / FLOATING_MODULUS); }

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static

static int g(void); /* funktionsprototyp */ void f(int a) { /* funktionsdefinition */ .... /* g() är tillgängligt här, */ } /* men inte i andra filer */ static int g(void) { /* funktionsdefinition */ .... }

register

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#include <stdio.h> int main(void) { printf(” The universe is never ending! ”); main(); return 0; /* kommer aldrig att nås! */ }

int sum(int n) { if (n <= 1) return n; else return (n + sum(n-1)); } sum(1) 1 sum(2) 2 + sum(1) eller 2 + 1 sum(3) 3 + sum(2) eller 3 + 2 + 1 sum(4) 4 + sum(3) eller 4 + 3 + 2 + 1

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0! = 1, n! = n(n-1) ... 3*2*1 för n > 0 eller ekvivalent 0! = 1 n! = n((n-1)!) för n > 0

int factorial(int n) { if (n <= 1) /* antar att n inte är negativt */ return 1; else return (n* factorial(n-1)); }

int factorial(int n) { int product = 1; for (; n > 1; --n) product *= n; return product; }

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#include <stdio.h> void wrt_it(void); int main(void) { printf(”Input a line: ”); wrt_it(); printf(”\n\n”); return 0; } void wrt_it(void) { int c; if ((c = getchar()) != ’\n’) wrt_it(); putchar(c); }

while

for

f0 = 0, f1 = 1, fi+1 = fi + fi-1 för i = 1, 2, ...

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int fibonacci(int n) { if (n <= 1) return n; else return (fibonacci(n-1) + fibonacci(n-2)); } /* n fibonacci(n) antalet funktionsanrop som läggs på stacken 1 1 1 1 2 1 3 .... 42 267914296 866988873 43 433494437 1402817465 .... */