C# String ToUpper() Method

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# 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);
    }
}

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# 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);
    }
}

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# 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);
    }
}

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.