int a , b;
a = a + b;
b = a - b;
a = a - b;    

Example:
a  = 5 , b = 3
a = 5 + 3 = 8  // new value of a is 8
b = 8 - 3 = 5  // new value of b
a = 8 - 5 = 3  // now a = 3 and b = 5