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C# String Replace() Method - GeeksforGeeks

Last Updated : 11 Mar, 2025

In C#, the Replace() method is used to replace all occurrences of a specified substring or character in a string with another substring or character. This method is particularly useful for string manipulation tasks, such as formatting or cleaning up data.

Example 1: Using Replace() method to replace "World" with "Geeks" in a string.

// C# program to illustrate 
// the use of Replace() Method
using System; 

class Geeks 
{ 	
	public static void Main() 
	{ 		
		// String initialization and Declaration
		string s = "Hello, World";

		// Before Replacing 
		Console.WriteLine("Before Replacing: " + s);

		// Using Replace() method
		s = s.Replace("World", "Geeks");

		// After Replacing
		Console.WriteLine("After Replacing: " + s);		
	} 
} 

Before Replacing: Hello, World
After Replacing: Hello, Geeks

Explanation: In the above example, we use a Replace() method of the String class to replace the World with Geeks.

public string Replace(char oldChar, char newChar)
public string Replace(string oldValue, string newValue)

Parameters:

• oldChar: The character which is to be replaced.
• newChar: The new character will be replaced with the old character.
• oldValue: The old substring which is to be replaced.
• newValue: New substring that will replace with the old value.

Return Type:

• This method returns a new string (System.String) in which all the occurrences of the previous value change with the specified values.

Exceptions:

• ArgumentNullException: If OldValue or Oldchar both are null.
• ArgumentException If OldValue or Oldchar is the empty string ("").

Example 2: Using the Replace() method to replace all occurrences of a specified substring with a new substring.

// Using Replace(String oldValue, String newValue) method
using System;

class Geeks
 {
    static void Main(string[] args) 
    {
        string s = "Hello, Geek";
        string res = s.Replace("Geek", "Geeks");
        Console.WriteLine("" + res);
    }
}

Explanation: In the above example, the Replace() method replaces "Geek" with "Geeks" in the original string and returns a new string.

Example 3: Using the Replace() method to replace the specified character from the string.

// Using the Replace() method to replace the 
// specified character from the string
using System;

class Geeks
{
    static void Main(string[] args) 
    {
        string s = "Hello, World!";
        
        string res = s.Replace('o', 'a');
        Console.WriteLine("Modified String: " + res);
    }
}

Modified String: Hella, Warld!

Explanation: In the above example, we use the Replace() method which replaces all occurrences of a specified character with a new character. As shown the character 'o' replaces with 'a'.

Example 4: Using the Replace() method in a Case-Sensitive Manner.

// Using Replace() method with Case Sensitive 
using System;
class Geeks
{
    static void Main(string[] args) {
        
        string s = "Hello, World!";
        string res = s.Replace("hello", "Geeks");
        Console.WriteLine("" + res);
    }
}

Explanation: In the above example, the string value passed as "hello" (lowercase) is not found in the original string, so no replacement were done because it is cases case-sensitive operation.

Example 5: Performing multiple replacement operations on the String (Replacement’s Chain) using the Replace() method.

// Perfroming Multiple Replacements
// at the same time
using System;

class Geeks 
{
    static void Main(string[] args) 
	{
        string s = "Hello, World! Welcome to the World of C#!";

        string res = s.Replace("World", "Geeks").Replace("C#", "C Sharp");

        Console.WriteLine("Modified String: " + res);
    }
}

Modified String: Hello, Geeks! Welcome to the Geeks of C Sharp!

Explanation: In the above example, the multiple replacement operation is performed using the Replace() method of string class the world "World" with "Geeks" and "C#" with "C Sharp" using method chaining.

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