C#:
Converting a string to lower case

How to:

In C#, you can convert a string to lowercase using the ToLower() or ToLowerInvariant() methods. Here’s how:

string originalText = "Hello, World!";
string lowerCaseText = originalText.ToLower();

Console.WriteLine(lowerCaseText); // Prints: hello, world!

And for culture-invariant conversions:

string mixedCaseText = "İstanbul";
string lowerInvariantText = mixedCaseText.ToLowerInvariant();

Console.WriteLine(lowerInvariantText); // Prints: i̇stanbul

Sample output:

hello, world!
i̇stanbul

Deep Dive

Historically, the need to convert strings to lowercase stems from computer systems that started with case-insensitive commands. Nowadays, we still do this for three main reasons:

1. Consistency: When treating inputs, especially user-generated data, converting to lowercase ensures a standardized format.
2. Case-Insensitive Operations: This includes searching, sorting, and comparing strings where “Apple” should be treated the same as “apple”.
3. Localization: Languages have different rules for casing. ToLowerInvariant() addresses this by providing a culture-independent conversion, turning characters to lowercase based on invariant culture (akin to English) and avoiding unexpected results.

Alternatives to .ToLower() and .ToLowerInvariant() include using regular expressions for replacements or manually iterating through a string for custom conversion scenarios.

Implementation detail wise, these methods do not modify the original string; strings in .NET are immutable. They create and return a new string that is the lowercase version of the original.

See Also

• String Class in C# Documentation: Microsoft Docs
• StringComparison Enum and Culture-Invariant Comparisons: Microsoft Docs