求半徑爲r的圓的內接正n邊形的面積。要求: r和n由鍵盤輸入

#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; 

}