Indexing arrays

Every item in an array has an index. This represents where the item is located within the array.

The index starts from 0 for the first item, 1 for the second item, and so on.

Reading an item from an array

Let’s say we have an array of numbers:

//     index:      0   1   2   3   4
int[] numbers = { 10, 20, 30, 40, 50 };

We can get the first item (which is 10) by using its index 0:

int firstNumber = numbers[0]; // firstNumber is 10

Or, we can get the third item (which is 30) by using its index 2:

int thirdNumber = numbers[2]; // thirdNumber is 30

Then, we can print these values:

Console.WriteLine(firstNumber); // Output: 10
Console.WriteLine(thirdNumber); // Output: 30

Or, to print them directly:

Console.WriteLine(numbers[0]); // Output: 10
Console.WriteLine(numbers[2]); // Output: 30

Modifying an item in an array

We can also change an item in the array by using its index. For example, to change the second item (which is 20) to 25, we can do:

numbers[1] = 25;
// Now the array is { 10, 25, 30, 40, 50 }

Finding the length of an array

We can find out how many items are in an array by using the Length property:

int length = numbers.Length; // length is 5
Console.WriteLine(length); // Output: 5

It is important to remember that since array indexing starts at 0, the last index of an array is always Length - 1. For example, in our numbers array, the last index is 4 (since 5 - 1 = 4).