The ```Array``` class in the ```System``` namespace provides the **`Resize()` method**, which can be used to #key# update: increase or decrease #key# the size of an existing array in C#.

# Syntax

```
public static void Resize<T> (ref T[]? array, int newSize);
```
It takes the one-dimensional array to resize and returns its new size as input. 

# Notes


- If the new length is *equal to* the length of the old array, this method does not do anything.
- If the new length is *greater than* the existing length of the array, an array of the new length is created, and all the elements of the old array are copied over to the new array.
- If the user-provided new length is *less than* the length of the existing array, a new array is created, and elements of the existing array are copied until the new array is filled. The rest of the exiting array elements are ignored.
- This method only works on one-dimensional arrays.
- This is an O(n) complexity method, where n is the new length of the array.



In the code below, we have created an array of strings named ```months``` to store the names of the first three months of a quarter.

Let's say we now want to store all  twelve months of the year. We will resize the same ```months``` array for this, and use the ```Array.Resize()``` method to pass `12` as the new `Length` of the array.

```
 Array.Resize(ref months, months.Length + 9);
```

Notice that after the resize operation, the length of the array is `12`, and it has space to store another nine strings.


```
Initial-Months Array - Length : 3
0 : January
1 : Feburary
2 : March

After Resize-Months Array : Length : 12
0 : January
1 : Feburary
2 : March
3 : 
4 : 
5 : 
6 : 
7 : 
8 : 
9 : 
10 : 
11 : 
 ```

# Code


using System;

public class ArrayResizer
{
    public static void Main()  {

        String[] months = {"January","Feburary", "March"};

      
        Console.WriteLine("Initial-Months Array - Length : {0}",months.Length );
        PrintArray(months);

        Array.Resize(ref months, months.Length + 9);
        
        Console.WriteLine("After Resize-Months Array : Length : {0}",months.Length);
        PrintArray(months);       
    }

    public static void PrintArray(String[] array)  {
        for(int i = 0; i < array.Length; i++)
        {
            Console.WriteLine("{0} : {1}", i, array[i]);
        }
        Console.WriteLine();
    }
}

How to resize an array in C#

Use Array.Resize in C# to increase or decrease one-dimensional array size by copying existing elements.