using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        Console.WriteLine("what".Truncate(4));

        Console.WriteLine("qqqqqqqqqq".Truncate(4));

        Console.WriteLine("qqqqqqqqqq".Truncate(6));

        Console.WriteLine("qqqqqqqqqq".Truncate(20));

    }

}

​

public static class Extensions

{

    public static string Truncate(this string current, int length)

    {

        return current.Truncate(length, " ...");

    }

    public static string Truncate(this string current, int length, string suffix)

    {

        if (string.IsNullOrEmpty(current)) current = "";

        if (current.Length <= length) return current;

        if (length <= suffix.Length) return current.Substring(0, length);

        length = Math.Max(0, length - suffix.Length);

        return current.Substring(0, length) + suffix;

    }

}