Problem: ns7
    Swap 2 values
#include <stdio.h>             Trace
main()   first   second  temp
{  
     int first, second, temp; ---       ---       ---
   
     first = 1;   1        ---        ---
     second = 2;   1       2          ---
     temp = first;   1       2           1
     first = second;   2       2           1
     second = temp;  
      
     return 0;        
}