18. Implementing swap( ) function

• swap( ) is a function that swaps values of two integer variables:

  
      void swap( int* px, int* py )
      {
          int temp = *px;
          *px = *py;
          *py = temp;
      }
  
      int main( )
      {
          int x = 5;
          int y = 10;
          swap( x, y );   // Error: must take address
          swap( &x, &y ); // Correct
          return 0;
      }