#include <iostream>
#include <iomanip>
#include <cmath>

using namespace std;

#define _USE_MATH_DEFINES

int main()
{
    double a = 0;
    double b = 0;
    char choice = 'x';

    cout << "Zadejte rovinny obrazec, jehoz obsah a obvod chcete spocitat: a - ctverec, b - obdelnik, c - kruh" << endl;
    cin >> choice;

    if(choice == 'a')
    {
        cout << "Zadejte stranu ctverce:" << endl;
        cin >> a ;

        if(cin.fail() || a<=0)
        {
            cout << "Nespravny vstup." << endl;
        }
        else
        {
            cout << "Obsah ctverce je: "  << fixed << setprecision(4) << a*a << endl;
            cout << "Obvod ctverce je: "  << fixed << setprecision(4) << 4*a << endl;

        }
    }
    else if (choice == 'b')
    {
        cout << "Zadejte strany obdelniku:" << endl;
        cin >> a >> b ;

        if(cin.fail() || a<=0 || b<=0)
        {
         cout << "Nespravny vstup." << endl;
        }
        else
        {
            cout << "Obsah obdelniku je: "  << fixed << setprecision(4) << a*b << endl;
            cout << "Obvod obdelniku je: "  << fixed << setprecision(4) << 2*a+2*b << endl;
        }
    }
    else if (choice == 'c')
    {
        cout << "Zadejte polomer kruznice:" << endl;
        cin >> a ;

        if(cin.fail() || a<=0)
        {
         cout << "Nespravny vstup." << endl;
        }
        else
        {
            cout << "Obsah kruznice je: "  << fixed << setprecision(4) << M_PI*a*a << endl;
            cout << "Obvod kruznice je: "  << fixed << setprecision(4) << 2*M_PI*a << endl;
        }
    }
    else
    {
        cout << "Nespravny vstup." << endl;
    }
    return 0;
}