453页第八题的程序怎么写

#include <iostream>
#include<cmath>
#include<iomanip>
 
#define PI  3.1416
#define sq  2
 
using namespace std;
 
double distance(double x1, double x2, double y1, double y2);
double raduis(double x1, double x2, double y1, double y2);
double circumference(double r);
double area(double r);
 
 
 
int main(int argc, char *argv[])
{
     double x1;
     double x2;
     double y1;
     double y2;
     
    
    cout<<"Enter the x and y cordinates of center of the circle: ";
    cin>>x1>>y1;
    
    cout <<endl<<"Enter the x and y coordinates of a point on the circle: ";
    cin>>x2>>y2;
    
    
        cout<<endl<<"Raduis = "<<fixed<<setprecision(2)<<raduis(x1,x2,y1,y2)<<endl;
        
        cout<<"Diameter = "<<raduis(x1,x2,y1,y2) + raduis(x1,x2,y1,y2)<<endl;
        
        cout<<"Circumference = "<<circumference(raduis(x1,x2,y1,y2))<<endl;
        
        cout<<"Area = "<<area(raduis(x1,x2,y1,y2))<<endl;
        
        
   system("pause");
    return 0;
}
 
double distance(double x1, double x2, double y1, double y2)
{         
      return sqrt(pow(x2 - x1, sq) + pow(y2 - y1, sq));                    
}
 
double raduis(double x1, double x2, double y1, double y2)
{
  return distance(x1, x2, y1, y2);                                   
}
 
double circumference(double r)
{
   return sq * PI * r;
}
 
double area(double r)
{
   return PI * pow(r, sq);
}