18. swap using xor

 X = 5  = 0101

Y = 9  = 1001

x = x ^ y    = 0101    = 1001    = 1100 ( = 12 )

y = x ^ y    = 1100    = 1001    = 0101 ( = 5 = Y)

x = x ^ y     = 1100     = 0101     = 1001 ( = 9 = X)

Code :

#include<bits/stdc++.h> using namespace std; int main() {        int x,y,t;     cin>>t;     while (t--)     {         cin>>x>>y;         x = x^y;         y = x^y;         x = x^y;         cout<<x<<' '<<y<<endl;     } }