Call by reference example swap function

#include<stdio.h>
void swap(int *a,int *b)
{
  int num;
  num=*a;
  *a=*b;
  *b=num;
  return;
}
int main()
{
  int x=34,y=25;
  printf("%d is %d\n",x,y);
  swap(&x,&y);
  printf("%d is %d \n",x,y);
  return 0;
}