求半径为r的圆的内接正n边形的面积。要求: r和n由键盘输入

#include<iostream>

using namespace std;

#include<cmath>

int main()

{

int r,n;

cout<<"please enter r and n:";

cin>>r>>n;

double s;

s=n*r*r*(sin(2*3.14)/n)/2;

cout<<"s="<<s<<endl;

return 0; 

}