using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication1
{
	class Program
	{
		static int VratInt(ref int cislo)
		{
			do { Console.WriteLine("Zadejte cele cislo"); } while (!(int.TryParse(Console.ReadLine(), out cislo)));
			return cislo;
		}
		public static void ZadejKoeficienty(ref int a, ref int b, ref int c)
		{
			int cislo = 0;
			Console.WriteLine("Kvadraticka rovnice ve tvaru ax^2+bx+c=0\nZadejte koeficient a");
			do
			{
				a = VratInt(ref cislo);
				if (a == 0) Console.WriteLine("Nejedna se o kvadratickou rovnici, ale o linearni rovnici.\nZadejte koeficient a ruzny od nuly");
			}
			while (a == 0);
			Console.WriteLine("Zadejte koeficient b");
			b = VratInt(ref cislo);
			Console.WriteLine("Zadejte koeficient c");
			c = VratInt(ref cislo);
			double d = (Math.Pow(b, 2) - 4) * a * c;
			if (d == 0)

				Console.WriteLine("Dvojnasobne reseni x={0}", -b / (2 * a));

			else
			if (d < 0)
				Console.WriteLine("Rovnice nema reseni v oboru realnych cisel");
			else
				Console.WriteLine("x1={0}, x2={1}", (-b + Math.Sqrt(d)) / (2 * a), (-b - Math.Sqrt(d)) / (2 * a));
		}

		static void Main(string[] args)
		{
			char volba = '9';
			int a = 0, b = 0, c = 0;

			do
			{
				Console.Clear();
				if (volba == '1') ZadejKoeficienty(ref a, ref b, ref c);
				Console.WriteLine("1..Zadani koeficientu a reseni kvadratickou rovnice \n------------\n0..Konec");
				volba = Console.ReadKey().KeyChar;
			} while (volba != '0');
		}
	}
}