swap

    double swap(double* px, double* py)

swap two numbers implicit, also also a function arguments are converted

/* 
 * swap example code
 * http://code-reference.com/c/stdio.h/swap
 */
#include <stdio.h> /* including standard library */
 
int main( void )
{
    int x=2, y=4;
 
    swap(x,y);
    printf("x=%d y=%d",x,y);
    return 0;
}

  x=4 y=2