IsUpper, IsLower

Some C# strings contain only lowercase letters. These strings do not need to be lowercased. By testing first, we can avoid excess work.

We must implement our own custom IsLower and IsUpper methods. We add them with extension methods in a static class.

Example

This program contains a static class of extension methods. The IsUpper and IsLower methods are public static methods written with the extension method syntax.

using System;

static class Extensions
{
    public static bool IsUpper(this string value)
    {
        // Consider string to be uppercase if it has no lowercase letters.
        for (int i = 0; i < value.Length; i++)
        {
            if (char.IsLower(value[i]))
            {
                return false;
            }
        }
        return true;
    }

    public static bool IsLower(this string value)
    {
        // Consider string to be lowercase if it has no uppercase letters.
        for (int i = 0; i < value.Length; i++)
        {
            if (char.IsUpper(value[i]))
            {
                return false;
            }
        }
        return true;
    }
}

class Program
{
    static void Main()
    {
        Console.WriteLine("test".IsLower()); // True
        Console.WriteLine("test".IsUpper());
        Console.WriteLine("Test".IsLower());
        Console.WriteLine("Test".IsUpper());
        Console.WriteLine("TEST3".IsLower());
        Console.WriteLine("TEST3".IsUpper()); // True
    }
}
True
False
False
False
False
True

Syntax

We used extension method syntax. In large projects, using a static class of extension methods is often simpler than trying to remember different static methods in different classes.

We implemented IsUpper and IsLower for strings. These methods perform a fast scanning of the source string, rather than requiring another allocation and conversion.