using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        string numberString = "one;two;three;four;five;six";

        Console.WriteLine("Known Index Result:");

        WriteResult(RemoveWithKnownIndex(numberString, 3)); //Removes 3rd index

        Console.WriteLine("Known Indexes Result:");

        WriteResult(RemoveWithKnownIndexes(numberString, new [] { 2, 3 })); //Removes 2nd and 3rd index

        Console.WriteLine("Unknown Index Result:");

        WriteResult(RemoveWithUnknownIndex(numberString, "four")); //Removes all items that match "four"

​

    }

    private static IEnumerable<string> RemoveWithKnownIndex(string input, int index)

    {

        var inputList = input.Split(';').ToList();

        inputList.RemoveAt(index);

        return inputList;

    }

    private static IEnumerable<string> RemoveWithKnownIndexes(string input, IEnumerable<int> indexes)

    {

        var inputList = input.Split(';').ToList();

        foreach(int index in indexes)

        {

            inputList.RemoveAt(index);

        }

        return inputList;

    }

    private static IEnumerable<string> RemoveWithUnknownIndex(string input, string userInput)

    {

        return input.Split(';').Where(x => string.Compare(x, userInput, true) != 0);

    }

    private static void WriteResult(IEnumerable<string> input)

    {           

        Console.WriteLine(string.Join(";", input));

        Console.WriteLine();

    }

}