using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        string test=@"thats a\n\ntest\nwith multiline \n\nthings";

        bool result=checkForSpecialChars(test);

        Console.WriteLine(result);

    }

    public static bool checkForSpecialChars(string testString)

    {

        string characterList = @"^([a-zA-Z0-9äöüÄÖÜß\-|()[\]/%'<>_?!=,*. ':;#+\\])+$";

        foreach (var item in testString)

        {

            if (characterList.Contains(item))

            {

                return true;        

            }

        }

        return false;

    }

}