C# String ToUpper() Method (original) (raw)

Last Updated : 05 Mar, 2025

In C#, the **ToUpper() method is used to convert all characters in a string to uppercase. If a character has an uppercase letter, it is converted, otherwise, it remains unchanged. Special characters and symbols are unaffected. This method is commonly used for case-insensitive comparisons and text formatting.

**Example 1: Basic Usage of ToUpper() Method

C# `

// C# program to demonstrate ToUpper() method using System;

class Geeks { public static void Main() { // Declare and initialize a string string s1 = "GeeksForGeeks";

    // Convert string to uppercase
    string s2 = s1.ToUpper();
    
    // Print original and converted strings
    Console.WriteLine("String Before Conversion: " + s1);
    Console.WriteLine("String After Conversion: " + s2);
}

}

`

Output

String Before Conversion: GeeksForGeeks String After Conversion: GEEKSFORGEEKS

**Explanation: In this example, the ToUpper() method converts all lowercase letters in the string "GeeksForGeeks" to uppercase, resulting in "GEEKSFORGEEKS"

Syntax of String ToUpper() Method

public string ToUpper();

public string ToUpper(System.Globalization.CultureInfo culture);

• **Parameters: **culture (optional): A CultureInfo object that defines culture-specific casing rules.
• **Return Type: The method returns a new string in which all characters have been converted to uppercase.

**Example 2: Using String.ToUpper()

C# `

// C# program to demonstrate ToUpper() method using System;

class Geeks { public static void Main() { // Declare and initialize a string string s1 = "This is C# Program xsdd_$#%";

    // Convert string to uppercase
    string s2 = s1.ToUpper();
    
    // Print the converted string
    Console.WriteLine(s2);
}

}

`

Output

THIS IS C# PROGRAM XSDD_$#%

**Explanation: In this example, all alphabetic characters in the string are converted to uppercase, while special characters remain unchanged.

**Example 3: Using String.ToUpper(CultureInfo)

C# `

// C# program to demonstrate // ToUpper(CultureInfo) method using System; using System.Globalization;

class Geeks { public static void Main() { // Declare and initialize a string string s1 = "This is C# Program xsdd_$#%";

    // Convert string to uppercase using 
    // English (United States) culture
    string s2 = s1.ToUpper(new CultureInfo("en-US", false));

    // Print the converted string
    Console.WriteLine(s2);
}

}

`

Output

THIS IS C# PROGRAM XSDD_$#%

**Explanation: In this example, the ToUpper(CultureInfo) method allows specifying a culture for case conversion. It ensures the consistency across different language settings.

**Notes:

• The ToUpper() method does not modify the original string, it returns a new uppercase string.
• If the CultureInfo parameter is null, an ArgumentNullException is thrown.
• This method is useful for case-insensitive operations, such as string comparisons.