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

Last Updated : 23 Apr, 2025

The **Insert() method in C# is a part of the String class. It is used to insert a new string at a specified index position and return a new string with the inserted string value. This method does not make the changes in the original string because strings are immutable in C#. It returns a new modified string.

Now, let us go through a simple example to understand the usage of this method.

**Example 1: Use of the **Insert() method to add a new string at a specified index position.

C# `

// C# program to illustrate the // method string Insert(int startIndex, string value) using System;

class Geeks { public static void Main() { // original string String s = "GeeksGeeks";

    Console.WriteLine("Given String: " + s); 

    // Insert "for" at index 5
    String res = s.Insert(5, "for");
    
    // New string after insertion
    Console.WriteLine("After Inserting : " + res);

    // Insert " " (space) at index 8
    res = s.Insert(5, " ");
    
    Console.WriteLine("After Inserting : " + res);
}

}

Output

Given String: GeeksGeeks After Inserting : GeeksforGeeks After Inserting : Geeks Geeks

**Syntax of String Insert() Method

public string Insert(int Indexvalue, string value)

**Parameters:

**Indexvalue: It is the index position of the **in current string where the new value will be inserted. The type of this parameter is **System.Int32.
value: The String value to be inserted. The type of this parameter is **System.String.

**Return Type: Returns a new modified string with a value inserted at the specified position. The return type is **System.String.

**Exceptions:

**ArgumentNullException: If the String value is null.
**ArgumentOutOfRangeException: If Indexvalue is negative or greater than the length of the string.

**Note: String is immutable in C#. This methods cannot modify the original string instead it return a new string with the applied changes.

Example 2: Inserting a string in the specific index position using the Insert() method.

C# `

// C# program to demonstrate the // Insert method using System;

class Geeks { public static void Main() { // string declaration and initialization String str = "Geeks";

    // String before insert operation
    Console.WriteLine("Current string: " + str); 

    // insert Geeks at index 5 where string is append 
    Console.WriteLine("New string: " + str.Insert(5, "forGeeks")); 
}

}

Output

Current string: Geeks New string: GeeksforGeeks

**Example 3: Inserting the country code at the starting of the number provided by user, using Insert() method (Real-World use case).

C# `

// Using the Insert() method to // add the country code in strating of // number provided by user using System;

class Geeks { public static void Main() { // string declaration and initialization String num = "357-xxx-xxxx";

    // String before insert operation
    Console.WriteLine("Current string: " + num); 

    // Country code of india to be inserted
    String code = "+91-";

    // insert india's contry code at 
    // index 0 where string is append 
    Console.WriteLine("New string: " + num.Insert(0, code)); 
}

}

Output

Current string: 357-xxx-xxxx New string: +91-357-xxx-xxxx

**Explanation: In the above example, we use Insert() method to add contry code in the starting of a number. This method is very usefull for inserting different values in a specific position of a string.