5_II_9_ы

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

namespace ForDZ
{
    class Input
    {
        private IEnumerator<string> istream;

        private static IEnumerable<string> GetNullStream()
        {
            while (true) yield return null;
        }

        private static IEnumerator<string> GetIStream()
        {
            while (true)
            {
                IEnumerable<string> sstream;
                try
                {
                    sstream = Console.ReadLine().Split().Where(s => s.Length > 0);
                }
                catch (Exception)
                {
                    sstream = GetNullStream();
                }

                foreach (string s in sstream)
                    yield return s;
            }
        }

        public Input()
        {
            istream = GetIStream();
        }

        public string GetString()
        {
            istream.MoveNext();
            return istream.Current;
        }

        public int GetInt()
        {
            return int.Parse(GetString());
        }
    }

    class Program
    {
        static Input reader;

        static void Pause()
        {
            Console.WriteLine("Press any key.");
            Console.ReadKey();
        }

        static int nod(int a, int b)
        {
            while (a > 0 && b > 0)
            {
                if (a > b)
                {
                    a %= b;
                }
                else
                {
                    b %= a;
                }
            }

            return a + b;
        }

        static void task_1()
        {
            Console.Write("> ");
            int a = reader.GetInt();
            int b = reader.GetInt();

            do
            {
                int del = nod(a, b);

                if (del == 1) break;

                a /= del;
                b /= del;
            }
            while (a != 1 && b != 1);

            Console.WriteLine($"> {a} / {b}");
        }

        static void task_2()
        {
            Console.Write("> ");
            int a = reader.GetInt();
            int b = reader.GetInt();

            int res = 0;
            for (int i = ((a > b) ? a : b), end = a * b + 1; i < end; i++)
            {
                if (i % a == 0 && i % b == 0)
                {
                    res = i;
                    break;
                }
            }

            Console.WriteLine($"> {res}");
        }

        static void task_3()
        {
            Console.Write("> ");
            int a = reader.GetInt();
            int b = reader.GetInt();

            int c = reader.GetInt();
            int d = reader.GetInt();

            int x = 0, y = 0;

            if (b != d)
            {
                Console.Write($"> ({a} / {b}) == ");

                do
                {
                    int del = nod(a, b);

                    if (del == 1) break;

                    a /= del;
                    b /= del;
                }
                while (a != 1 && b != 1);

                Console.WriteLine($"({a} / {b})");

                Console.Write($"> ({c} / {d}) == ");

                do
                {
                    int del = nod(c, d);

                    if (del == 1) break;

                    c /= del;
                    d /= del;
                }
                while (c != 1 && d != 1);

                Console.WriteLine($"({c} / {d})");

                Console.WriteLine($"> ({a} / {b}) + ({c} / {d})");

                if (b != d)
                {
                    Console.WriteLine($"> ({a} * {d} + {c} * {b}) / ({b} * {d})");
                    x = a * d + c * b;
                    y = d * b;
                }
                else
                {
                    Console.WriteLine($"> ({a} + {c}) / {b}");
                    x = a + c;
                    y = b;
                }
            }
            else
            {
                Console.WriteLine($"> ({a} / {b}) + ({c} / {d})");
                Console.WriteLine($"> ({a} + {c}) / {b}");
                x = a + c;
                y = b;
            }

            Console.WriteLine($"> ({x} / {y})");

            do
            {
                int del = nod(x, y);

                if (del == 1) break;

                x /= del;
                y /= del;
            }
            while (x != 1 && y != 1);

            Console.WriteLine($"> {x} / {y}");
        }

        static void task_4()
        {
            Console.Write("> ");

            //int a = reader.GetInt();
            //int b = reader.GetInt();

            int n = reader.GetInt();
            int[] a = new int[n];

            for (int i = 0; i < n; i++)
            {
                a[i] = reader.GetInt();
            }

            bool have_not_zero = true;

            for (int i = 0; i < n; i++)
            {
                if(a[i] == 0)
                {
                    have_not_zero = false;
                    break;
                }
            }

            if(!have_not_zero)
            {
                Console.WriteLine("1");
                return;
            }


            while (have_not_zero)
            {
                int i_min = 0;
                int min = a[i_min];

                for (int i = 1; i < n; i++)
                {
                    if(a[i] < min)
                    {
                        i_min = i;
                        min = a[i];
                    }
                }

                for (int i = 0; i < n; i++)
                {
                    if (i == i_min) continue;

                    a[i] %= min;
                }

                for (int i = 0; i < n; i++)
                {
                    if (a[i] == 0)
                    {
                        have_not_zero = false;
                        break;
                    }
                }
            }

            int res = a[0];

            for (int i = 1; i < n; i++)
            {
                if (a[i] != 0  && (res == 0 || a[i] < res))
                {
                    res = a[i];
                }
            }

            //for (int i = 0; i < n; i++) Console.Write($"{a[i]} "); Console.WriteLine();
            Console.WriteLine($"> {res}");

            //int res = nod(a, b);

            //Console.WriteLine($"> {res}");
        }

        static void Main(string[] args)
        {
            ConsoleKeyInfo key;
            reader = new Input();

            for (; ; )
            {
                Console.Clear();
                Console.WriteLine("Select:");
                Console.WriteLine(" 1) fraction");
                Console.WriteLine(" 2) NOK");
                Console.WriteLine(" 3) fraction sum");
                Console.WriteLine(" 4) NOD");
                Console.WriteLine(" 0) exit");

                key = Console.ReadKey();
                Console.Clear();

                switch (key.Key)
                {

                    case ConsoleKey.D1:
                        task_1();
                        Pause();
                        continue;
                    case ConsoleKey.D2:
                        task_2();
                        Pause();
                        continue;
                    case ConsoleKey.D3:
                        task_3();
                        Pause();
                        continue;
                    case ConsoleKey.D4:
                        task_4();
                        Pause();
                        continue;
                }

                if (key.Key == ConsoleKey.D0) break;
            }

            //Console.ReadKey();
        }
    }
}