with the help of 2way mechine instuctions,its possible
ex:
         strcat(s1,s2)
               means    s1=s1+s2,
            or else
            a+=b means   a=a+b.

I am afraid i understood the question. If the question is
defined like, u need to exchange two variables without using
a temporary variable is,

a += b; 
b = a - b; 
a = a - b;
Another methos is , 
a ^= b ^= a ^= b;

#include<stdio.h>
#include<conio.h>
int main()
{
  int x=10,y=15; 
 x = x+y;
printf("%d",x);
     getch();
     }