using System;

public class Program

{

    public static void Main()

    {

        //Тази програма конвертира мерни единици.

        Console.WriteLine("Въведете число за преобразуване.");

        var num = int.Parse(Console.ReadLine());

        //Функцията var се използва когато трябва да въвеждаме числа.//

        //Чрез въведената функция по долу трабва да въведете входната мерна единица.//

            Console.WriteLine("Въведете входната мерна единица:");

            string sourse = Console.ReadLine().ToLower();

        //Чрез въведената функция по долу трабва да въведете изходната мерна единица.//

            Console.WriteLine("Въведете изходната мерна единица:");

            string exit = Console.ReadLine().ToLower();

            double result = 0.00;   

         if (sourse == "mm" && exit == "mm")

            {

                result = num * 1;

            }

            if (sourse == "mm" && exit == "cm")

            {

                result = num / 10;

            }

            if (sourse == "mm" && exit == "m")

            {

                result = num / 1000;

            } 

            if (sourse == "mm" && exit == "mi")

            {

                result = (num / 1000) * 0.000621371192;

            } 

            if (sourse == "mm" && exit == "in")

            {

                result = (num / 1000) * 39.3700787;

            }

            if (sourse == "mm" && exit == "km")

            {

                result = (num / 1000) * 0.001;

            }

            if (sourse == "mm" && exit == "ft")

            {

                result = (num / 1000) * 3.2808399;

            }

            if (sourse == "mm" && exit == "yd")

            {

                result = (num / 1000) * 1.0936133;

            }

            if (sourse == "cm" && exit == "mm")

            {

                result = num * 10;

            }

            if (sourse == "cm" && exit == "cm")

            {

                result = num * 1;

            }

            if (sourse == "cm" && exit == "m")

            {

                result = num / 100;

            }

            if (sourse == "cm" && exit == "mi")

            {

                result = (num / 100) * 0.000621371192;

            }

            if (sourse == "cm" && exit == "in")

            {

                result = (num / 100) * 39.3700787;

            }

            if (sourse == "cm" && exit == "km")

            {

                result = (num / 100) * 0.001;

            }

            if (sourse == "cm" && exit == "ft")

            {

                result = (num / 100) * 3.2808399;

            }

            if (sourse == "cm" && exit == "yd")

            {

                result = (num / 100) * 1.0936133;

            }

            if (sourse == "m" && exit == "mm")

            {

                result = num * 1000;

            }

            if (sourse == "m" && exit == "cm")

            {

                result = num * 100;

            }

            if (sourse == "m" && exit == "mi")

            {

                result = num * 0.000621371192;

            }

            if (sourse == "m" && exit == "in")

            {

                result = num * 39.3700787;

            }

            if (sourse == "m" && exit == "km")

            {

                result = num * 0.001;

            }

            if (sourse == "m" && exit == "ft")

            {

                result = num * 3.2808399;

            }

            if (sourse == "m" && exit == "yd")

            {

                result = num * 1.0936133;

            }

            if (sourse == "mi" && exit == "mm")

            {

                result = (num / 0.000621371192) * 1000;

            }

            if (sourse == "mi" && exit == "cm")

            {

                result = (num / 0.000621371192) * 100;

            }

            if (sourse == "mi" && exit == "m")

            {

                result = num / 0.000621371192;

            }

            if (sourse == "mi" && exit == "mi")

            {

                result = num * 1;

            }

            if (sourse == "mi" && exit == "in")

            {

                result = (num / 0.000621371192) * 39.3700787;

            }

            if (sourse == "mi" && exit == "km")

            {

                result = (num / 0.000621371192) * 0.001;

            }

            if (sourse == "mi" && exit == "ft")

            {

                result = (num / 0.000621371192) * 3.2808399;

            }

            if (sourse == "mi" && exit == "yd")

            {

                result = (num / 0.000621371192) * 1.0936133;

            }

            if (sourse == "in" && exit == "mm")

            {

                result = (num / 39.3700787) * 1000;

            }

            if (sourse == "in" && exit == "cm")

            {

                result = (num / 39.3700787) * 100;

            }

            if (sourse == "in" && exit == "m")

            {

                result = (num / 39.3700787);

            }

            if (sourse == "in" && exit == "mi")

            {

                result = (num / 39.3700787) * 0.000621371192;

            }

            if (sourse == "in" && exit == "in")

            {

                result = num * 1;

            }

            if (sourse == "in" && exit == "km")

            {

                result = (num / 39.3700787) * 0.001;

            }

            if (sourse == "in" && exit == "ft")

            {

                result = (num / 39.3700787) * 3.2808399;

            }

            if (sourse == "in" && exit == "yd")

            {

                result = (num / 39.3700787) * 1.0936133;

            }

            if (sourse == "km" && exit == "mm")

            {

                result = (num / 0.001) * 1000;

            }

            if (sourse == "km" && exit == "cm")

            {

                result = (num / 0.001) * 100;

            }

            if (sourse == "km" && exit == "m")

            {

                result = num / 0.001;

            }

            if (sourse == "km" && exit == "mi")

            {

                result = (num / 0.001) * 0.000621371192;

            }

            if (sourse == "km" && exit == "in")

            {

                result = (num / 0.001) * 39.3700787;

            }

            if (sourse == "km" && exit == "km")

            {

                result = 1 * num;

            }

            if (sourse == "km" && exit == "ft")

            {

                result = (num * 1000) * 3.2808399;

            }

            if (sourse == "km" && exit == "yd")

            {

                result = (num / 0.001) * 1.0936133;

            }

            if (sourse == "ft" && exit == "mm")

            {

                result = (num / 3.2808399) * 1000;  

            }

            if (sourse == "ft" && exit == "cm")

            {

                result = (num / 3.2808399) * 100;

            }

            if (sourse == "ft" && exit == "m")

            {

                result = num / 3.2808399;

            }

            if (sourse == "ft" && exit == "mi")

            {

                result = (num / 3.2808399) * 0.000621371192;

            }

            if (sourse == "ft" && exit == "in")

            {

                result = (num / 3.2808399) * 39.3700787;

            }

            if (sourse == "ft" && exit == "km")

            {

                result = (num / 3.2808399) * 0.001;

            }

            if (sourse == "ft" && exit == "ft")

            {

                result = (num / 3.2808399) * 3.2808399;

            }

            if (sourse == "ft" && exit == "yd")

            {

                result = (num / 3.2808399) * 1.0936133;

            }

            if (sourse == "yd" && exit == "mm")

            {

                result = (num / 1.0936133) * 1000;

            }

            if (sourse == "yd" && exit == "cm")

            {

                result = (num / 1.0936133) * 100;

            }

            if (sourse == "yd" && exit == "m")

            {

                result = (num / 1.0936133);

            }

            if (sourse == "yd" && exit == "mi")

            {

                result = (num / 1.0936133) * 0.000621371192;

            }

            if (sourse == "yd" && exit == "in")

            {

                result = (num / 1.0936133) * 39.3700787;

            }

            if (sourse == "yd" && exit == "km")

            {

                result = (num / 1.0936133) * 0.001;

            }

            if (sourse == "yd" && exit == "ft")

            {

                result = (num / 1.0936133) * 3.2808399;

            }

            if (sourse == "yd" && exit == "yd")

            {

                result = (num / 1.0936133) * 1.0936133;

            }

            Console.WriteLine(result + "" + exit);

        }

    }

​

​