using System;

public class a_bruch

{

    public static void Main()

    {

        int  z1=0, n1=0, z2=0, n2=0, eingabe;

        do 

        {

            Console.WriteLine("Hauptmenü");

            Console.WriteLine("1 - 1. Bruch");

            Console.WriteLine("2 - 2. Bruch");

            Console.WriteLine("3 - Addition");

            Console.WriteLine("4 - Subtraktion");

            Console.WriteLine("5 - Multiplikation");

            Console.WriteLine("6 - Division");

            Console.WriteLine("0 - Ende");

            eingabe=int.Parse(Console.ReadLine());

            switch (eingabe) 

            {

                case 1: Console.WriteLine("1. Zähler");

                        z1=int.Parse(Console.ReadLine());

                        Console.WriteLine("1. Nenner");

                        n1=int.Parse(Console.ReadLine());

                    break;

                case 2: Console.WriteLine("2.Zähler");

                        z2=int.Parse(Console.ReadLine());

                        Console.WriteLine("2.Nenner");

                        n2=int.Parse(Console.ReadLine());

                    break;

                case 3: Console.WriteLine("Ergebnis");

                        s_bruch.addition(z1,z2,n1,n2);

                    break;

                case 4: Console.WriteLine("Ergebnis");  

                        s_bruch.subtraktion(z1,z2,n1,n2);

                    break;

                case 5: Console.WriteLine("Ergebnis");

                        s_bruch.multiplikation(z1,z2,n1,n2);

                    break;  

                default:

            Console.WriteLine("Falsche Auswahl!");

                break;

            }            

        } while (eingabe!=0);

​

    }

}

class s_bruch

{

    public static void multiplikation(int z1, int z2, int n1, int n2)

    {

        int ze;

        ze = z1*z2;

        int ne;

        ne = n1*n2;

        Console.WriteLine(ze);

        Console.WriteLine(ne);

    }   

    public static void addition(int z1, int z2, int n1, int n2)

    {

        int ne;

        ne = n1*n2;

        int ze;

        ze= z1*n2+z2*n1;

        Console.WriteLine(ze);

        Console.WriteLine(ne);

    }

    public static void subtraktion(int z1, int z2, int n1, int n2)

    {

        int ne;

        ne = n1*n2;

        int ze;

        ze= z1*n2-z2*n1;

        Console.WriteLine(ze);

        Console.WriteLine(ne);

    }   

    public static void division(int z1, int z2, int n1, int n2)

    {

        int ze;

        ze = z1*n2;

        int ne;

        ne = n1*z2;

        Console.WriteLine(ze);

        Console.WriteLine(ne);

    }   

}