using System;

using System.Collections;

using System.Collections.Generic;

using System.IO;

public class Program

{

    public static void Main()

    {

        StreamReader inputFile = File.OpenText(@"C:\test.txt");

        //use List instead of array since you are stream the file and don't know how many lines there are in total and a list can increase dynamically, where as an array would need to be resized

        List<string> lefts = new List<string>();

        List<string> rights = new List<string>();

        while (!inputFile.EndOfStream)

        {

            var line = inputFile.ReadLine(); //read the line eg. 10000,56

            var splittedLine = line.Split(','); //split the line into parts seperated by , eg. 10000,56 will result in an array of length 2 where index 0 is 10000 and index 1 is 56

            var left = splittedLine[0]; //read index 0 to get eg. 10000

            var right = splittedLine[1]; //read index 1 to get eg. 56

            lefts.Add(left); //add left to a list

            rights.Add(right); //add right to a list

            listBox1.Items.Add(line); //fill the listBox1 with the line

            listBox1.Items.Add("Left: " + left + " | Right: " + right); //if desired, fill the listBox1 with the left and right part

        }

    }

}