程序代码：

#include <iostream>
#include <cmath>
using namespace std;
int main()
{int i=0,b,n,pi=2;
cin>>n;
for(b=0;b<=n;b++)
{
i=sqrt(i+2);
pi=pi*(2/i);
}
cout<<pi<<endl;
}

程序代码：

#include <iostream>
#include <cmath>
using namespace std;

int main( void )
{
    size_t n;
    cin >> n;

    double pi = 2;
    double tmp = 0;
    for( size_t i=0; i!=n+1; ++i )
    {
        tmp = sqrt(tmp+2.0);
        pi *= 2.0/tmp;
    }

    cout << pi << endl;
}