s.c

#include<stdio.h>
main()
{
	int a=10, b=20, t;
	int *pa=&a, *pb=&b;
	t=*pa;
	*pa=*pb;
	*pb=t;
	printf("%d %d\n", *pa, *pb);

	a=10, b=20, t=NULL;
	*pa=&a, *pb=&b;
	t=*pa;
	*pa=*pb;
	*pb=t;
	printf("%d %d\n", *pa, *pb);
}