include <bits/stdc++.h>
using namespace std;
double r, pi=3.14159;
int main()
{
cin >> r;
cout << fixed << setprecision(4) << r2 << " ";
cout << fixed << setprecision(4) << r2pi << " ";
cout << fixed << setprecision(4) << pir*r;
}
反思：错误点：double 使用错误
