How to add to end of array C#?

Question

How do I add a new item from a TextBox and Button on a Windows Form at the end of an ArrayList which references a class?

private product[] value = new product[4];

value[1] = new product("One",5)
value[2] = new product("Two",3)
value[3] = new product("Three",8)

Workflow

• Enter new products details into textbox1, textbox2, textbox3

• When I click Add the new product gets added to the array:

  value[1] = new product("One",5)
value[2] = new product("Two",3)
value[3] = new product("Three",8)
value[4] = new product("Four",2)

What is the code for doing this?

Answer 1

Arrays are fixed size, which means you can't add more elements than the number allocated at creation time, if you need a auto sizing collection you could use List<T> or an ArrayList

Example:

// using collection initializers to add two products at creation time
List<Product> products = new List<Product>{new Product("One",5), new Product("Two",3) };

// then add more elements as needed
products.Add(new Product("Three",8));

Answer 2

Use List as other people mentioned. If you are set on arrays, use

Array.Resize<Product>(ref product, your new size);

If you're only going to be adding a couple of products (over the lifetime of your array) just do something like

Array.Resize<Product>(ref product, product.Length + 1);

If you are going to be adding a lot of products, you might want to do something similar to what List does - like this:

Array.Resize<Product>(ref product, product.Length * 2);

Answer 3

I think you need a List<product> collection, looking at your code. Then just call the Add() method on it

Answer 4

You can't add items to an array, you would have to create a new array that is larger and copy the items to it. There is a method for that, which is somewhat misleadingly named Resize as it doesn't actually resize the array:

Array.Resize<product>(ref value, 5);

If you want to add items to a collection, you should use a List instead:

private List<product> value = new List<product>();
value.Add(new product("One",5));
value.Add(new product("Two",3));
value.Add(new product("Three",8));

value.Add(new product("Four",2));

Edit:
If you want to resize the array, you might want to increase the size instead of resizing it to a specific value:

int index = value.Length;
Array.Resize<product>(ref value, index + 1);
value[index] = ...

Answer 5

Arrays are zero indexed, so an array initialized to a size of 4 could only be accessed up to index 3...

If you wanted the array to grow, then you'd have to either initialize the array at least as large as you wanted to be able to grow to, or else you'd have to create a new array with the new larger size and copy the old array over; not very efficient.

In this case, you'd do better to use a collection like a list, rather than an array, so that the size can dynamically increase.

Answer 6

You should probably also take a look at Array versus List: When to use which?

Answer 7

Array.Resize is not an efficient method. It creates a new array with the new size then copy old array values to the new array and then replaces the old array with the new array. As you can see this is not a very efficient way of appending an item.

Unless it is a requirement that you have no control on use a List instead of array or create an array with maximum expected dimension from the beginning.

For more explanation consider this example: You created an array that can hold million items and fill it with objects. You want to add the million and one object to the array. You use Array.Resize method to change array size to 1000001. When the method tries to create a new array of 1000001 items and copy the items from old array to new array you may get an out of memory error because you are trying to have TWO arrays of a million (holding 2 millions objects) in memory at the same time while all the items that you need are one million +1. Although consider the time and resources lost in creating, copying and replacing.