#include <stdio.h>

// Quadruple the value pointed to by a. 
void quadruple(int *a)
{
	*a = *a * 4;
}

int main(void)
{
	int x = 5;
	printf("x before: %d\n", x); 
	quadruple(&x);
	printf("x after: %d\n", x); 
	return 0;
}