#define _USE_MATH_DEFINES
#include <iostream>
#include <cmath>
#include <cstdio>
#include <iomanip>

using namespace std;

int main()
{
    double S, O, a, b, r;
    char sw;

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

    switch (sw)
    {
    case 'a':
         {
        cout << "Zadejte stranu ctverce:" << endl;
        cin >> a;

        if (cin.fail() || a<=0)
        {
            cout << "Nespravny vstup." << endl;
                    return 0;
        }
        else
        {
            S = a * a;
            O = 4 * a;

            cout << "Obsah ctverce je: " << fixed << setprecision(4) << S << endl;
            cout << "Obvod ctverce je: " << fixed << setprecision(4) << O << endl;
            break;
        }
    }
    case 'b':
         {
        cout << "Zadejte strany obdelniku:" << endl;
        cin >> a >> b;
        if ((a>0) && (b>0))
        {
            S = a * b;
            O = 2 * (a + b);

            cout << "Obsah obdelniku je: " << fixed << setprecision(4) << S << endl;
            cout << "Obvod obdelniku je: " << fixed << setprecision(4) << O << endl;
        }
        else (cin.fail());
            cout << "Nespravny vstup." << endl;
        return 0;
        }
    case 'c':
         {
        cout << "Zadejte polomer kruznice:" << endl;
        cin >> r;
        if (r>0)
        {
            S = M_PI * r * r;
            O = 2 * M_PI * r;

            cout << "Obsah kruznice je: " << fixed << setprecision(4) << S << endl;
            cout << "Obvod kruznice je: " << fixed << setprecision(4) << O << endl;
        }
        else (cin.fail());
            cout << "Nespravny vstup." << endl;
            system("pause");
        return 0;

    default: cout << "Nespravny vstup." << endl;

    }
}

    return 0;
}