C/Function/Function

A program with two functions

<source lang="cpp">

1. include <stdio.h>

void f(void); /* prototype for f() */ int main(void) {

 printf("I ");
 f();
 printf("java2s.com.");
 return 0;

} void f(void) {

 printf("like ");

}

      </source>

A simple program that demonstrates sum()

<source lang="cpp">

1. include <stdio.h>

void sum(int x, int y); int main(void) {

 sum(12, 230);
 sum(94, 63);
 sum(851, 39);
 return 0;

} void sum(int x, int y) {

 printf("%d ", x + y);

}

      </source>

Assign function return value to a variable

<source lang="cpp">

1. include <stdio.h>

int f(void); int main(void) {

 double answer;
 answer = f();
 printf("%f", answer);
 return 0;

} int f(void) {

 return 100;

}

      </source>

Check out the int value change before and after function call

<source lang="cpp">

1. include <stdio.h>

void f(int *k) {

 *k = *k + 10; 

} main () {

 int i;
 i = 0;
   
   printf (" i before call %d \n", i);
 f(&i); 
   printf ("i after call %d \n", i);

}

      </source>

Define function and return value

<source lang="cpp">

1. include <stdio.h>

int f(void); int main(void) {

 char ch;
 ch = f();
 printf("%c", ch);
 return 0;

} int f(void) {

 return "a";

}

      </source>

Define function and use it

<source lang="cpp">

1. include <stdio.h>

int f(void); /* prototype */ int main(void) {

 int num;
 num = f( );
 printf("%d", num);
 return 0;

} int f(void) {

 return 10;

}

      </source>

Define function and use it: square

<source lang="cpp">

1. include <stdio.h>

int sqr(int x); int main(void) {

 int t=10;
 printf("%d %d", sqr(t), t);
 return 0;

} int sqr(int x) {

 x = x * x;
 return( x );

}

      </source>

Define function to calculate the ounces and cups

<source lang="cpp">

1. include <stdio.h>

int ounces_to_cups(int o); int main(void) {

 int ounces;
 int cups;
 printf("Enter ounces: ");
 scanf("%d", &ounces);
 cups = ounces_to_cups(ounces);
 printf("%d cups", cups);
 return 0;

} int ounces_to_cups(int o) {

 return o / 8;

}

      </source>

Define function to calculate the volumn

<source lang="cpp">

1. include <stdio.h>

double volume(double s1, double s2, double s3); int main(void) {

 double vol;
 vol = volume(12.2, 5.67, 9.03);
 printf("Volume: %f", vol);
 return 0;

} double volume(double s1, double s2, double s3) {

 return s1 * s2 * s3;

}

      </source>

Define function to multiply two int

<source lang="cpp">

1. include <stdio.h>

int mul(int a, int b); int main(void) {

 int x, y, z;
 x = 10;   
 y = 20;
 z = mul(x, y);           /* 1 */
 
 printf("%d", mul(x,y));  /* 2 */
 
 mul(x, y);               /* 3 */
 return 0;

} int mul(int a, int b) {

 return a * b;

}

      </source>

Define function to output char

<source lang="cpp">

1. include <stdio.h>

void printchar(char ch); int main(void) {

 printchar("A");
 printchar("B");
 printchar("C");
 return 0;

} void printchar(char ch) {

 printf("%c", ch);

}

      </source>

Define function to sum

<source lang="cpp">

1. include <stdio.h>

int sum(int i1, int i2,int i3) {

  return (i1 + i2 + i3);

} int main() {

   printf("Sum is %d\n", sum(1, 2, 3));
   return (0);

}

      </source>

Define function with parameter and return value

<source lang="cpp">

1. include <stdio.h>

double f(); int main(void) {

 printf("%f", f(10.2));
 return 0;

} double f(double num) {

 return num / 2.0;

}

      </source>

Define function with void return

<source lang="cpp">

1. include <stdio.h>

void outputnum(int num); int main(void) {

 outputnum(10);
 return 0;

} void outputnum(int num) {

 printf("%d", num);

}

      </source>

Define two functions and call them in main

<source lang="cpp">

1. include <stdio.h>

void f1(void); void f2(void); int main(void) {

 f1();
 f2();
 return 0;

} void f1(void) {

 printf("f1, ");

} void f2(void) {

 printf("f2.");

}

      </source>

Define two functions and make function call

<source lang="cpp">

1. include <stdio.h>

void f1(void), f2(void); int main(void) {

 f1();
 return 0;

} void f1(void) {

 int i;
 for(i = 0; i < 10; i++) 
     f2();

} void f2(void) {

 int i;
 for(i = 0; i < 10; i++) 
     printf("%d ", i);

}

      </source>

Definition of the function to calculate an average

<source lang="cpp">

1. include <stdio.h>

float average(float x, float y) {

  return (x + y)/2.0f;

} /* main program - execution always starts here */ void main() {

  float average(float x, float y);  /* Function prototype */
  float value1 = 1.0F;
  float value2 = 2.0F;
  float r = 0.0F;

  r = average(value1, value2);
  printf("\nThe average is: %f",  r);

}

      </source>

Demonstraction of function call

<source lang="cpp"> void f2(void){

  printf ("2 \n");
  

} void f1 (void) {

 printf ("1 \n");
 printf ("1 \n");
 f2 ( );
 printf ("1 \n");
 printf ("1 \n");

}

int main ( ) {

 printf ("\n");
 printf ("\n");
 printf ("\n");
 printf ("\n");
 printf ("\n");
            f1();
 printf ("\n");
 printf ("\n");
 printf ("\n");
 printf ("\n");
   return 0;

}

      </source>

Function call

<source lang="cpp">

void f(int k) {

 k = k + 10;

} int main ( ) {

 int i = 0;
 
   printf ("i before call %d \n", i);
 f(i);
   printf (" i after call %d \n", i);

}

      </source>

Function call each other

<source lang="cpp">

1. include <stdio.h>

void f2(int b); void f1(int a); int main(void) {

 f1(30);
 return 0;

} void f1(int a) {

 if( a ) 
     f2( a - 1 );
 printf("%d ", a);

} void f2(int b) {

 printf(" . ");
 if(b) 
     f1( b - 1 );

}

      </source>

Function declaration

<source lang="cpp">

1. include <stdio.h>

int area(int l, int w); int main(void) {

 printf("area is %d", area(100, 130));
 return 0;

} int area(l, w) int l, w; {

 return l * w;

}

      </source>

Function: Print a string in uppercase

<source lang="cpp">

1. include <stdio.h>
2. include <ctype.h>

void print_upper(char *string); int main(void) {

 char s[80];
 printf("Enter a string: ");
 gets(s);
 print_upper(s); 
 printf("\ns is now uppercase: %s", s);
 return 0;

} void print_upper(char *string) {

 register int t;
 for(t=0; string[t]; ++t)  {
   string[t] = toupper(string[t]);
   putchar(string[t]);
 }

}

      </source>

Function prototype

<source lang="cpp">

1. include <stdio.h>

void f(void); int main(void) {

 f();
 f();
 return 0;

} void f(void) {

 int i = 10;
 printf("%d ", i);

}

      </source>

Function prototype: declare getnum() prior to its first use

<source lang="cpp">

1. include <stdio.h>

/* declare getnum() prior to its first use */ float getnum(void) {

 float x;
 printf("Enter a number: ");
 scanf("%f", &x);
 return x;

} int main(void) {

 float i;
 i = getnum();
 printf("%f", i);
 return 0;

}

      </source>

Function to output square

<source lang="cpp">

1. include <stdio.h>

void sqrF(int num); int main(void) {

 sqrF(10.0);
 return 0;

} void sqrF(int num) {

 printf("%d", num * num);

}

      </source>

Function which returns int value

<source lang="cpp">

1. include <stdio.h>

int convert(void); int main(void) {

 printf("%d", convert());
 return 0;

} int convert(void) {

 int dollars;
 printf("Enter number of dollars: ");
 scanf("%d", &dollars);
 return dollars / 8;

}

      </source>

Global and local variable inside function

<source lang="cpp">

1. include <stdio.h>

int count; /* global count */

void f(void) {

 int count; /* local count */
 count = 100;
 printf("count in f() : %d\n", count);

} int main(void) {

 count = 10;
 f();
 printf("count in main(): %d\n", count);
 return 0;

}

      </source>

Return statement

<source lang="cpp">

1. include <stdio.h>

void f(void); int main(void) {

 f();
 return 0;

} void f(void) {

 printf("Here.");
 return; /* return with no value */
 printf("Never.");

}

      </source>

Serve as a prototype within this program

<source lang="cpp">

1. include <stdio.h>

void f(int a, int b) {

 printf("%d ", a % b);

} int main(void) {

 f(10,3);
 return 0;

}

      </source>

This program has three functions

<source lang="cpp">

1. include <stdio.h>

void f1(void); /* prototypes */ void f2(void); int main(void) {

 f2( );
 printf("3");
 return 0;

} void f2(void) {

 f1();
 printf("2 ");

} void f1(void) {

 printf("1 ");

}

      </source>

Uses a function prototype to enforce strong type checking

<source lang="cpp"> void sqr_it(int *i); /* prototype */ int main(void) {

 int x;
 x = 10;
 sqr_it(x);  /* type mismatch */
 return 0;

} void sqr_it(int *i) {

 *i = *i * *i;

}

      </source>