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.

C# method notes

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.