1 #include <stdio.h>
 2 int diff(int x, int y);//the first form
 3 void interchange(int *u, int *v);//the second form
 4 int main(void){
 5     int x = 9;
 6     int y = 5;
 7     int z;
 8     printf("The Originally x = %d and y = %d\n", x, y);//alter variables in the calling function
 9     interchange(&x, &y);
10     z = diff(x, y);//need a value for some calculation or action
11     printf("Now  x = %d and y = %d\n", x, y);
12     printf("z = %d\n", z);
13     return 0;
14 }
15 
16 int diff(int x, int y){
17     return(x - y);
18 }
19 
20 void interchange(int *u,int *v){
21     int temp;
22 
23     temp = *u;
24     *u = *v;
25     *v = temp;
26 }