swapping of 2 numbers without using 3rd variable in C language.

#include

main()

{

     int w,q;

     printf("/n enter two no's");

     scanf("%d%d",&w,&q);

      printf("/n before swapping");

      printf ("%d%d",w,q);

              w=w+q;                                  /*sum of 2 variables*/

              q=w-q;                                   /*sum of 2 variables*/

              q=w-q;                                  /*sum of 2 variables*/

      printf("/n after swapping");

      printf("%d%d",w,q);                  

}