Replace a C# array with a new array of different size

To replace a C# array with a new array of different size, use the Array.Resize method. This method allows you to change the size of an existing array, either expanding or shrinking it while preserving existing elements.

Syntax

Following is the syntax for using Array.Resize −

Array.Resize<T>(ref array, newSize);

Parameters

• array − The array to resize (passed by reference using ref)

• newSize − The new size of the array

How It Works

When you resize an array:

• If the new size is larger, existing elements are preserved and new elements are initialized to their default values

• If the new size is smaller, elements beyond the new size are removed

• The original array reference is replaced with the new array

Using Array.Resize to Shrink an Array

Example

using System;

class Program {
   static void Main() {
      char[] arr = new char[5];
      arr[0] = 'J';
      arr[1] = 'A';
      
      Console.WriteLine("Original Array Length: " + arr.Length);
      
      // Resize to smaller size
      Array.Resize<char>(ref arr, 4);
      
      // Set values for new elements
      arr[2] = 'C';
      arr[3] = 'K';
      
      Console.WriteLine("Resized Array Length: " + arr.Length);
      Console.WriteLine("Updated Array: " + new string(arr));
   }
}

The output of the above code is −

Original Array Length: 5
Resized Array Length: 4
Updated Array: JACK

Using Array.Resize to Expand an Array

Example

using System;

class Program {
   static void Main() {
      int[] numbers = {10, 20, 30};
      
      Console.WriteLine("Original Array: [" + string.Join(", ", numbers) + "]");
      Console.WriteLine("Original Length: " + numbers.Length);
      
      // Resize to larger size
      Array.Resize<int>(ref numbers, 6);
      
      // Add new elements
      numbers[3] = 40;
      numbers[4] = 50;
      numbers[5] = 60;
      
      Console.WriteLine("Expanded Array: [" + string.Join(", ", numbers) + "]");
      Console.WriteLine("New Length: " + numbers.Length);
   }
}

The output of the above code is −

Original Array: [10, 20, 30]
Original Length: 3
Expanded Array: [10, 20, 30, 40, 50, 60]
New Length: 6

Key Points

• Reference parameter − The array must be passed using ref keyword

• Performance − Creates a new array internally, so use sparingly for large arrays

• Type safety − Must specify the generic type parameter

• Default values − New elements are initialized to default values for the type

Conclusion

The Array.Resize method provides a convenient way to change the size of existing arrays in C#. It preserves existing elements when possible and automatically handles memory allocation, making it ideal for dynamic array size management in applications.