#include<iostream.h>
const float PAI=3.14159265;
float squre(float r)
{
    return PAI*r*r;
}
float square(float high=0,float length=0)
{
    return high*length;
}
float (*fs)(float,float=0);
void main()
{
    fs=&square;
    cout<<"the circle's squre is "<<fs(0)<<'\n';
}