2146: 【例7.2】与圆相关的计算

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