#include <stdio.h>

int cubeByValue( int n );

int main()
{
   int number = 5;

   printf( "The original value of number is %d", number );
   
   /* pass number by value to cubeByValue */
   number = cubeByValue( number );

   printf( "nThe new value of number is %dn", number );

   return 0;
}

int cubeByValue( int n ) {
   return n * n * n;  
}
 

The original value of number is 5

The new value of number is 125

#include <stdio.h>
int sum(int x, int y)
{
  return x + y;
}
int product(int x, int y)
{
  return x * y;
}
int difference(int x, int y)
{
  return x - y;
}
int main(void)
{
  int a = 10;
  int b = 5;
  int result = 0;
  int (*pfun)(int, int);              /* Function pointer declaration      */
  pfun = sum;            
  result = pfun(a, b);                /* Call sum() through pointer        */
  printf("npfun = sum             result = %d", result);
  pfun = product;        
  result = pfun(a, b);                /* Call product() through pointer    */
  printf("npfun = product         result = %d", result);
  pfun = difference;      
  result = pfun(a, b);                /* Call difference() through pointer */
  printf("npfun = difference      result = %dn", result);
  return 0;
}
 

pfun = sum             result = 15

     pfun = product         result = 50