超出范围但在范围内？

Question

So I want to learn the periodic table but I want to program a game to do it (It will be a console window). So the first code is the class for an element, its pretty easy...

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

namespace PeriodicTableGame
{
    class Element
    {
        int AtomicNumber;
        double AtomicMass;
        string Name;
        int Period;
        int Group;
        bool isLanthanide;
        bool isActanide;
        int isMetal; // 0 = Non Metal, 1 = Metaloid, 2 = Metal
        int stateAtRT; // 0 = Solid, 1 = Liquid, 2 = Gas, 3 = Plasma (68     Degrees F, 20 Celcius, 293.15 Kelvin)

        int Block; // 0 = s, 1 = d, 2 = p, 3 = f

        public Element(int atomicNumber, double atomicMass, int period, int group, bool islanthanide, bool isactanide, int ismetal, int stateatrt, int block)
        {
            AtomicNumber = atomicNumber;
            AtomicMass = atomicMass;
            Period = period;
            Group = group;
            isLanthanide = islanthanide;
            isActanide = isactanide;
            isMetal = ismetal;
            stateAtRT = stateatrt;
            Block = block;
        }
    }

So that block is good so far, and now the second block...

class Data
{
    public static List<Element> ElementList = new List<Element>();

    public static List<Element> AddToList()
    {
        Element Nothing = new Element(0, 0, 0, 0, false, false, 0, 0, 0);
        Element Hydrogen = new Element(1, 1.008, 1, 1, false, false, 0, 2, 0);
        Element Helium = new Element(2, 4.003, 1, 18, false, false, 0, 2, 0);
        Element Lithium = new Element(3, 6.94, 2, 1, false, false, 0, 0, 0);
        Element Beryllium = new Element(4, 9.012, 2, 2, false, false, 2, 0, 0);
        Element Boron = new Element(5, 10.81, 2, 13, false, false, 1, 0, 2);
        Element Test = new Element(0, 0, 0, 0, false, false, 0, 0, 0);
        ElementList.Insert(0, Nothing);
        ElementList.Insert(1, Hydrogen);
        ElementList.Insert(2, Helium);
        ElementList.Insert(3, Lithium);
        ElementList.Insert(4, Beryllium);
        ElementList.Insert(5, Boron);
        ElementList.Insert(6, Test);
        return ElementList;
    }
}

That one is also good, and now the 3rd block...

class NumberGenerator
{
    public static int RandomNumberGenerator(int Min, int Max)
    {
        Random RandomGen = new Random();
        int RandomGenChoice = RandomGen.Next(Min, Max + 1);
        return RandomGenChoice;
    }
    public static Element RandomElementGenerator(int Number)
    {
        Element x = Data.ElementList.ElementAt(Number);
        return x;
    }
}

    class Program
{
    static void Main(string[] args)
    {
        int RNG = NumberGenerator.RandomNumberGenerator(1, 5);
        Element y = NumberGenerator.RandomElementGenerator(RNG);
    }

(Ignore the brackets I may have missed one on this post but they are fine in Visual Studio) I made a list of elements (I started with 5, and a 1st, and a test...) and tries to use the ElementGenerator on them but it gave an out of range exception, so I used an array, which is what you are looking at, and than I use the number 1 instead of 'Number' which is an Index no question, I put it in by hand, and I still got an out of range exception... WHY?

Answer 1

I would recommend you post this code to Code Review , because there are several things you could do more easily using C# features.

But going with the problem as it is...

Element y = NumberGenerator.RandomElementGenerator(i);

Are you sure this line is typed here as it is in your code? Because I could understand the error if it were really this:

Element y = NumberGenerator.RandomElementGenerator(j);  // j, not i

Here is what your Main method is doing:

static void Main(string[] args)
{
    // generate random number from 1 to 5
    int i = NumberGenerator.RandomNumberGenerator(5, 1);

    // print the number
    Console.WriteLine(i);

    // set j equal to (1 to 5) - 7 + 1 = (-6 to -1) [but this line is unused]
    int j = i - Data.ElementList.Count + 1;

    // Get an element in position -6 to -1
    Element y = NumberGenerator.RandomElementGenerator(j);

    // Wait for user to press a key
    Console.ReadKey();
}

If that fourth line is j as I believe, then you're trying to get the element at a position from -1 to -6, but an array will only have 0 and positive number positions.

You can use your debugger to find out what Number contains. When you get the exception, hover over Number to see what value it has. In Visual Studio 2017, it might show you this value automatically anyhow.

Answer 2

You are calling an empty list. Add items your Data.ElementList via Data.AddToList() first before calling the index.

    public static Element RandomElementGenerator(int Number)
    {
        Data.AddToList();
        Element x = Data.ElementList.ElementAt(Number);
        return x;
    }

Then you can call the index in the Data.ElementList .