#include<bits/stdc++.h>
using namespace std;
#define d double
int main()
{
    d n;cin>>n;
    cout<<fixed<<setprecision(4)<<n*2<<" "<<fixed<<setprecision(4)<<2*n*3.14159<<" "<<fixed<<setprecision(4)<<3.14159*n*n<<endl;
    return 0;
}

《printf 最好用的一集》

#include <bits/stdc++.h>
using namespace std;
double r;
int main() {
	cin >> r;
	printf("%.4f %.4f %.4f", r * 2, r * 2 * 3.14159, r * r * 3.14159);
	return 0;
}

#include<bits/stdc++.h> using namespace std; #define d double int main() { d n;cin>>n; cout<<fixed<<setprecision(4)<<n2<<" "<<fixed<<setprecision(4)<<2n3.14159<<" "<<fixed<<setprecision(4)<<3.14159n*n<<endl; return 0; }

#include<iostream>
#include<iomanip>
using namespace std;
int main(){
    double a,b,c,d;
    cin>>a;
    b=a*2;
    c=b*3.14159;
    d=a*a*3.14159;
    cout<<setprecision(4)<<fixed<<b<<" ";
    cout<<setprecision(4)<<fixed<<c<<" ";
    cout<<setprecision(4)<<fixed<<d;
}

#include<iostream>
#include<iomanip>
using namespace std;
int main(){
    double r,a,b,c;
    cin>>r;
    a=2*r;
    b=2*3.14159*r;
    c=3.14159*r*r;
    cout<<fixed<<setprecision(4)<<a;
    cout<<" ";
    cout<<fixed<<setprecision(4)<<b;
    cout<<" ";
    cout<<fixed<<setprecision(4)<<c;
    return 0;
}

#include<bits/stdc++.h> using namespace std; #define d double int main() { d n;cin>>n; cout<<fixed<<setprecision(4)<<n2<<" "<<fixed<<setprecision(4)<<2n3.14159<<" "<<fixed<<setprecision(4)<<3.14159n*n<<endl; return 0; }

//jazz

#include <bits/stdc++.h>

using namespace std;

int main(){
    double r;
    cin >> r;
    printf("%.4lf ",r * 2.0);
    printf("%.4lf ",2.0 * 3.14159 * r);
    printf("%.4lf ",3.14159 * r * r);
    return 0;
}

#include <bits/stdc++.h> using namespace std; double r, c, s, d; int main() { cin >> r; d = r * 2, c = d * 3.14159, s = r * r * 3.14159; cout << fixed << setprecision(4) << d << " " << c << " " << s << "\n"; return 0; }