change array size

Is it possible to change an array size after declaration? If not, is there any alternative to arrays?
I do not want to create an array with a size of 1000, but I do not know the size of the array when I'm creating it.

You can use Array.Resize(), documented in MSDN.

But yeah, I agree with Corey, if you need a dynamically sized data structure, we have Lists for that.

Important: Array.Resize() doesn't resize the array (the method name is misleading), it creates a new array and only replaces the reference you passed to the method.

An example:

var array1 = new byte[10];
var array2 = array1;
Array.Resize<byte>(ref array1, 20);

// Now:
// array1.Length is 20
// array2.Length is 10
// Two different arrays.

No, try using a strongly typed List instead.

For example:

Instead of using

int[] myArray = new int[2];
myArray[0] = 1;
myArray[1] = 2;

You could do this:

List<int> myList = new List<int>();
myList.Add(1);
myList.Add(2);

Lists use arrays to store the data so you get the speed benefit of arrays with the convenience of a LinkedList by being able to add and remove items without worrying about having to manually change its size.

This doesn't mean an array's size (in this instance, a List) isn't changed though - hence the emphasis on the word manually.

As soon as your array hits its predefined size, the JIT will allocate a new array on the heap that is twice the size and copy your existing array across.