Array access

Learn to access and modify array elements by index.

Array access

You access array elements by index. Indices start at zero: nums[0] is the first, nums[1] the second. Writing nums[i] = 99; updates the element.

An out-of-range index (for example nums[5] on a three-element array) throws an IndexOutOfRangeException. So make sure the index stays inside the bounds before using it.

Updating an element

You can assign new values to array elements: nums[0] = 99; turns the first element into 99. The array's size stays fixed, but its contents can change.

For example, to update the first score on a scoreboard you write scores[0] = 100;. This changes the content but keeps the array length the same; no new elements can be added.

Exercise Update the first element and print it

Declare a nums array with the value { 1, 2, 3 }. Update the first element with nums[0] = 10;. Then print nums[0] with Console.WriteLine. The output should be 10.

Show example solution

Write int[] nums = { 1, 2, 3 }; nums[0] = 10; Console.WriteLine(nums[0]);
Example solution:
using System;

class Program
{
    static void Main()
    {
        int[] nums = { 1, 2, 3 };
        nums[0] = 10;
        Console.WriteLine(nums[0]);
    }
}

Test yourself

Write the index of the second element

int[] nums = {10, 20, 30};
int second = nums[____];

Show answer

int[] nums = {10, 20, 30};
int second = nums[1];

With int[] nums = {10, 20, 30}; what is nums[1]?
```
int[] nums = {10, 20, 30};
Console.WriteLine(nums[1]);
```
- 10
- 20
- 30
- Error
Show answer

20 — Correct. nums[1] gives 20, the second element.
Match each index to its value

nums[0]

First element
nums[1]

Second element
nums[2]

Third element
nums.Length - 1

Last element

Next lesson: Array length

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