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

public class Test
{
	public static void Main()
	{
		var line = "[A] == [B] * 10 - FUNCTION([C], STRING_EXPRESSION, FUNCTION([D],[C],[E])), FUNCTION([C], [X]), 100";
        var matches = Regex.Matches(line, @"(?:(?:\((?>[^()]+|\((?<number>)|\)(?<-number>))*(?(number)(?!))\))|[^,])+");
        foreach (Match m in matches)
        	Console.WriteLine(m.Value.Trim());
        
	}
}