Swap values of two variables without using third variable [C]

Hello GuyZ,
    This question was asked by my brother(+1 CS Student). "How to swap values of two variables without using third variable in CPP?".
I didn't stuck the trick first... But later few seconds my mind stuck in this trick... I think the person who don't know any idea about it will create a brain storm... :p
[ NB: I'm not +1 CS student. :p I was Biology student ].

/* http://www.terminalcoders.blogspot.in _TERMINAL_CODERS_ PROGRAM TO SWAP VALUES OF TWO VARIABLES WITHOUT USING TEMPORARY VARIABLE */ #include <stdio.h> void main() { int a, b; printf("Enter value for 'A': "); scanf("%d", &a); printf("Enter value for 'B': "); scanf("%d", &b); printf("Before swap: \n\tA = %d\n\tB = %d", a, b); a = a+b; // or a = a*b; b = a-b; // or b = a/b; a = a-b; // or a = a/b; printf("\nAfter swap:\n\tA = %d\n\tB = %d\n\n", a, b); }