How to get the last five characters of a string using Substring() in C#?

string sub = input.Substring(input.Length - 5);

If your input string could be less than five characters long then you should be aware that string.Substring will throw an ArgumentOutOfRangeException if the startIndex argument is negative.

To solve this potential problem you can use the following code:

string sub = input.Substring(Math.Max(0, input.Length - 5));

Or more explicitly:

public static string Right(string input, int length)
{
    if (length >= input.Length)
    {
        return input;
    }
    else
    {
        return input.Substring(input.Length - length);
    }
}

If you can use extension methods, this will do it in a safe way regardless of string length:

public static string Right(this string text, int maxLength)
{
    if (string.IsNullOrEmpty(text) || maxLength <= 0)
    {
        return string.Empty;
    }

    if (maxLength < text.Length)
    {
        return text.Substring(text.Length - maxLength);
    }

    return text;
}

And to use it:

string sub = input.Right(5);