C# List test

using System;
using System.Collections;
using System.Collections.Generic;

class MainClass {
    static void Main() {
        Console.WriteLine("Hello World!");
        
        Console.WriteLine(Sum(100).ToString());
        Console.WriteLine(Sum2(100).ToString());
        Console.WriteLine(Sum3(100).ToString());
    }
    
    private static int Sum(int n)
    {
        ArrayList arrayList = new ArrayList();

        for (int i = 0; i < n; i++)
        {
            arrayList.Add(i+1);
        }

        int s = 0;

        for (int i = 0; i < arrayList.Count; i++)
        {
            s += (int)arrayList[i];
        }

        return s;
    }

    private static int Sum2(int n)
    {
        List<int> arrayList = new List<int>();

        for (int i = 0; i < n; i++)
        {
            arrayList.Add(i + 1);
        }

        int s = 0;

        for (int i = 0; i < arrayList.Count; i++)
        {
            s += (int)arrayList[i];
        }

        return s;
    }
    
    private static int Sum3(int n)
    {
        List<int> arrayList = new List<int>();

        for (int i = 0; i < n; i++)
        {
            arrayList.Add(i + 1);
        }

        int s = 0;

        foreach(int value in arrayList)
            s += value;
            
        return s;
    }
}