这个解最简单🤣

#include<bits/stdc++.h>
using namespace std;
int main(){
    cout<<"31.4159"<<endl<<"78.5398"<<endl<<"523.599";
    return 0;
}

#include<bits/stdc++.h>
using namespace std;
const double pai=3.141593;
const double n=5.0;
int main(){
    cout<<n*2*pai<<'\n'<<pai*n*n<<'\n'<<1.0*4/3*n*n*n*pai<<'\n';
    return 0;
}