C# String ToUpper

Summary: in this tutorial, you will learn how to use the C# String ToUpper() method to convert a string to uppercase.

Introduction to the C# ToUpper() method

The String ToUpper() method returns a copy of the current string converted to uppercase. Here’s the syntax of the ToUpper() method:

public string ToUpper();Code language: PHP (php)

The following example uses the ToUpper() method to convert the message "Hello, World!" to uppercase:

using static System.Console;

var message = "Hello, World!";
var upper = message.ToUpper();

WriteLine(upper);Code language: C# (cs)

Output:

HELLO, WORLD!Code language: plaintext (plaintext)

By default, the ToUpper() method takes the case rule of the current culture into the conversion. But if you want to convert a string to uppercase using a specific culture, you can use the following overload of the ToUpper() method:

public string ToLower (
   System.Globalization.CultureInfo? culture
);Code language: C# (cs)

In this syntax, the culture is an instance of CultureInfo that specifies a culture-specific casing rule.

For example, the following program illustrates how to use different CultureInfo objects can lead to different uppercase conversions based on specific language rules:

using System.Globalization;
using static System.Console;
var s = "istanbul İzmir Ankara";

// Using the default (English) culture
var englishUppercase = s.ToUpper(CultureInfo.InvariantCulture);
WriteLine("Default (English) uppercase: " + englishUppercase);

// Using the Turkish culture
var turkishCulture = new CultureInfo("tr-TR");
var turkishUppercase = s.ToUpper(turkishCulture);
WriteLine("Turkish uppercase: " + turkishUppercase);Code language: C# (cs)

In this example, we have a string that contains Turkish characters, such as "İ" (capital İ with a dot) and "İ" (small i with a dot) which are specific to the Turkish alphabet.

When we use the ToUpper() to convert a string to uppercase using the default culture (English), the method uses the English rules for uppercase conversion, and we get "ISTANBUL İZMIR ANKARA".

However, when we use the ToUpper() method with the Turkish culture ("tr-TR"), the method uses Turkish-specific uppercase rules for conversion.

In Turkish, the uppercase equivalent of "i" is "İ" without a dot, and the uppercase equivalent of "İ" is "I" (capital I without a dot). As a result, the Turkish uppercase string becomes "İSTANBUL İZMİR ANKARA".

C# String ToUpperInvariant()

The String ToUpperInvariant() returns an uppercase version of a string using the casing rules of the invariant culture.

Here’s the syntax of the ToUpperInvariant() method:

public string ToUpperInvariant();Code language: PHP (php)

The ToUpperInvariant() method is equivalent to the ToUpper() method with the CultureInfo.InvariantCulture argument:

ToUpper(CultureInfo.InvariantCulture)Code language: CSS (css)

One practical example of using the ToUpperInvariant() method is when you need to perform a case-sensitive string comparison.

Using ToUpperInvariant() ensures consistent behavior and avoids potential issues with culture-specific rules.

Summary

Use the C# String ToUpper() method to convert a string to uppercase.

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