C# String Insert() Method

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# 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);
	} 
}

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# 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")); 
	} 
} 

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).

// 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)); 
	} 
} 

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.