using System;
using System.Text;
using System.Text.RegularExpressions;

public class Test
{
	public static void Main()
	{
		var str = "dog:Cat,hi:Bye,num:,1,2,3,5,6,7,8,9,10,this:that";

		var result = Regex.Split(str, @",(?=\w+:)");
		foreach (var entry in result)
		    Console.WriteLine(entry);
	}
}