using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        string item = "a,b,c+1,2,3,4+z,x";

        var lists = item.Split('+').Select(i => i.Split(',')).ToList();

        IEnumerable<string> keys = null;

        foreach (var list in lists) 

        {

            keys = (keys == null) ? 

                list : 

                keys.SelectMany(k => list.Select(l => k + l));

        }

        foreach (var key in keys) 

        {

            Console.WriteLine(key); 

        }

    }

}