请教路过的大神，初识编程1个月，有关条件和各功能的调用问题，感激！

Question

菜鸟新手本人有一个作业，在控制台下的程序集A> 摄氏、华氏间温度转换器
  1>摄氏转华氏
  2>华氏转摄氏
  3>返回
B> 英尺、米长度转换器
  1>foot&inch to cm
  2>cm to foot&inch
  3>返回
C> 迈、千米/时 速度转换器
  1>kph to mph
  2>mph to kph
  3>返回
D> 油耗计算器
  1>
  2>
  3>返回
E> Exit（之前发帖问过一次，还被鄙视是野鸡大学。。呃，实在不是，是本人太菜。。现在有一些新的问题）问题1：如何做到从次级菜单返回主菜单啊？求详细的语句……光知道用循环，不知道咋循环。。
      还有作业要求每执行完一次运算，自动返回次级菜单，这个我也不会。。问题2：运算中会提示是否显示另外一种计算结果在，这时需要用户输入"Y"来进行，是不是要将这个Y转化成bool来    判断是否进行下一个操作呢？请问如何实现呢？问题3：用什么样的语句从主菜单调用各个function,这是我写的菜单代码：
 string menu = "\n1> Temperature calculator"
                          + "\n2> Length calculator"
                          + "\n3> Speed calculator"
                          + "\n4> Fuel consuption calculator"
                          + "\n5> Exit program";
            string menuOption,
                   subMenuOption,
                   TempCal,
                   LenthCal,
                   SpdCal,
                   FCCal;               Console.Write(menu);
            Console.WriteLine(" \n\nPlease enter your option..");
            menuOption = Console.ReadLine();            switch (menuOption)
            {
                case "1": menuOption = TempCal ;
                    break;
                case "2": menuOption = LenthCal;
                    break;
                case "3": menuOption = SpdCal;
                    break;
                case "4": menuOption = FCCal;
                    break;
                case "5": return;
                default: Console.WriteLine("Please enter a valid menu option");
                    break;
            }比如case 4，怎么做可以直接跳到油耗计算器去啊？
各个function之间应当保持什么样的关系呢？ 每个function的heading该怎么写？ static void什么的吗？
最后是我写的油耗计算器，里面有好多语句不通过>_<! 希望老鸟们猛烈批评指点…… static void Main(string[] args)
        {
            string readGallonOrLitre,
                   inputFuelUsed,
                   inputDistanceTravelled,
                   seeEqvltResult;
                   
            double fuelUsedGallon,
                   fuelUsedLitre,
                   distanceTravelledMile,
                   distanceTravelledKM,
                   fuelConsptMile,
                   fuelConsptKilo;
            int    
                   gallonOrLitre;
            bool   y;
            const  double KILOS_PER_MILE = 1.61,
                          MILES_PER_KILO = 0.62,
                          GALLON_PER_LITRE = 0.26,
                          LITRE_PER_GALLON = 3.76;            Console.WriteLine("Please select your prefered measurement...");
            Console.WriteLine("\nFor British imperial measure ( gallon and miles), please enter 1");
            Console.WriteLine("For metric measure ( kilometres and litre), please enter 2");
            Console.Write("\nNow please enter your option: ");            readGallonOrLitre = Console.ReadLine();
            gallonOrLitre = int.Parse(readGallonOrLitre);            switch (gallonOrLitre)
            {                case 1:
                    Console.Write("Please enter the amount of fuel used: ");
                    inputFuelUsed = Console.ReadLine();
                    fuelUsedGallon = double.Parse(inputFuelUsed);                    Console.Write("Please enter the distance travelled: ");
                    inputDistanceTravelled = Console.ReadLine();
                    distanceTravelledMile = double.Parse(inputDistanceTravelled);
                    fuelConsptMile = distanceTravelledMile / fuelUsedGallon;                    Console.WriteLine("Fuel consumption is " + fuelConsptMile + " gallons per mile");                    Console.WriteLine("\nDo you want to see the equivalent result in liters per 100 kilomitres?  \nIf yes enter y; if not enter anything to go back.");                    seeEqvltResult = Console.ReadLine();
                    y = Convert.ToBoolean(seeEqvltResult);
                    fuelConsptKilo = distanceTravelledMile * KILOS_PER_MILE / fuelUsedGallon * LITRE_PER_GALLON;
                    if (y)
                    {
                        Console.WriteLine("Your current fuel consumption is {0} per 100 kilometres", fuelConsptKilo);                    }
                    else
                        return;
                    break;                case 2:
                    Console.Write("Pleased enter the amount of fuel used: ");
                    inputFuelUsed = Console.ReadLine();
                    fuelUsedLitre = double.Parse(inputFuelUsed);                    Console.Write("Please enter the distance travelled: ");
                    inputDistanceTravelled = Console.ReadLine();
                    distanceTravelledKM = double.Parse(inputDistanceTravelled);
                    fuelConsptKilo = distanceTravelledKM / fuelUsedLitre;                    Console.WriteLine("Fuel consumption is " + fuelConsptKilo + " litres per kilometre");
                    Console.WriteLine("\nDo you want to see the equivalent result in gallons per 100 miles? \nIf yes enter y; if not enter anything to go back.");                    seeEqvltResult = Console.ReadLine();
                    y = Convert.ToBoolean(seeEqvltResult);
                    fuelConsptMile = distanceTravelledKM * MILES_PER_KILO / fuelUsedLitre * GALLON_PER_LITRE;                    if (y)
                    {
                        Console.WriteLine("Your current fuel consumption is {0} per 100 kilometres", fuelConsptMile);
                    }
                    else
                        return;
                    break;
最后的最后，如果有哪位大大愿意无私多帮助我一些，可以具体看看我写好的东西喝作业要求，在这里
https://drive.google.com/folderview?id=0B6tnQDOeCTi0VVJjbVc5Sjk2RTA&usp=sharing
编程条件功能

Answer 1

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;namespace ConsoleApplication1
{
    class Command
    {
        public char CommandKey { get; set; }
        public string CommandName { get; set; }
        public string InputPrompt { get; set; }
        public string OutputPrompt { get; set; }
        public Func<double, double> Action { get; set; }
    }    class Menu
    {
        public char CommandKey { get; set; }
        public string CommandName { get; set; }
        public List<Command> Commands { get; set; }
    }    class Program
    {
        static void Main(string[] args)
        {
            List<Menu> mainMenu = new List<Menu>()
            {
                new Menu()
                {
                    CommandKey = 'A',
                    CommandName = "摄氏、华氏间温度转换器",
                    Commands = new List<Command>() 
                    { 
                        new Command() { Action = x => 32.0 + x * 1.8, CommandKey = '1',
                                        CommandName = "摄氏转华氏", InputPrompt = "请输入摄氏温度：", 
                                        OutputPrompt = "{0}C = {1}F." },
                        new Command() { Action = x => (x - 32.0) / 1.8, CommandKey = '2',
                                        CommandName = "华氏转摄氏", InputPrompt = "请输入华氏温度：", 
                                        OutputPrompt = "{0}F = {1}C." }
                    }
                },
                new Menu()
                {
                    CommandKey = 'B',
                    CommandName = "英尺、米长度转换器",
                    Commands = new List<Command>() 
                    { 
                        new Command() { Action = x => x * 2.54, CommandKey = '1',
                                        CommandName = "foot&inch to cm", InputPrompt = "请输入inch：", 
                                        OutputPrompt = "{0}inch = {1}cm." },
                        new Command() { Action = x => x / 2.54, CommandKey = '2',
                                        CommandName = "cm to foot&inch", InputPrompt = "请输入cm：", 
                                        OutputPrompt = "{0}cm = {1}inch." }
                    }
                },
                new Menu()
                {
                    CommandKey = 'C',
                    CommandName = "迈、千米/时 速度转换器",
                    Commands = new List<Command>() 
                    { 
                        new Command() { Action = x => x * 1.609344, CommandKey = '1',
                                        CommandName = "mph -> kmph", InputPrompt = "请输入mph：", 
                                        OutputPrompt = "{0}mph = {1}kmph." },
                        new Command() { Action = x => x / 1.609344, CommandKey = '2',
                                        CommandName = "kmph -> mph", InputPrompt = "请输入kmph：", 
                                        OutputPrompt = "{0}kmph = {1}mph." }
                    }
                },
                new Menu()
                {
                    CommandKey = 'D',
                    CommandName = "油耗计算器",
                    Commands = new List<Command>()
                }
            };
            string inputKey = "";
            char exitKey = (char)(mainMenu.Max(x => x.CommandKey) + 1);
            while (inputKey != exitKey.ToString())
            {
                Console.Clear();
                Console.WriteLine("=====Main Menu=====");
                foreach (var menu in mainMenu)
                {
                    Console.WriteLine("{0}> {1}", menu.CommandKey, menu.CommandName);
                }
                Console.WriteLine("{0}> {1}", exitKey, "Exit");
                inputKey = Console.ReadLine().ToUpper();
                if (mainMenu.Any(x => x.CommandKey == inputKey.FirstOrDefault()))
                {
                    Menu menu = mainMenu.First(x => x.CommandKey == inputKey.FirstOrDefault());
                    char returnKey = (char)(menu.Commands.Select(x => x.CommandKey).DefaultIfEmpty('0').Max() + 1);
                    inputKey = "";
                    while (inputKey != returnKey.ToString())
                    {
                        Console.Clear();
                        foreach (var cmd in menu.Commands)
                        {
                            Console.WriteLine("{0}> {1}", cmd.CommandKey, cmd.CommandName);
                        }
                        Console.WriteLine("{0}> {1}", returnKey, "Return");
                        inputKey = Console.ReadLine().ToUpper();
                        if (menu.Commands.Any(x => x.CommandKey == inputKey.FirstOrDefault()))
                        {
                            Command cmd = menu.Commands.First(x => x.CommandKey == inputKey.FirstOrDefault());
                            Console.Write(cmd.InputPrompt);
                            double input = double.Parse(Console.ReadLine());
                            Console.WriteLine(cmd.OutputPrompt, input, cmd.Action(input));
                            Console.ReadKey();
                            inputKey = returnKey.ToString();
                        }
                    }
                    inputKey = "";
                }
            }
        }
    }
}