Array length

Learn to get the array length with .Length and understand bounds.

Array length

The .Length property gives the element count of an array. On a three-element array nums.Length returns 3. This is critical for setting loop bounds.

Valid indices run from 0 to nums.Length - 1. Accessing nums[nums.Length] always throws an error; the last valid index is Length - 1. That is why loops use i < nums.Length.

Bounds checking and loops

The safe way to walk an array is the pattern for (int i = 0; i < nums.Length; i++). Here i always stays between 0 and Length - 1; no error is raised.

Using .Length instead of hardcoding bounds makes the code robust; even if the array size changes, the loop adapts. So prefer .Length over constants like for (int i = 0; i < 5; i++).

Exercise Print the array length

Declare a nums array with the value { 7, 8, 9, 10, 11 }. Print nums.Length with Console.WriteLine. The output should be 5.

Show example solution

Write int[] nums = { 7, 8, 9, 10, 11 }; and print it with Console.WriteLine(nums.Length);
Example solution:
using System;

class Program
{
    static void Main()
    {
        int[] nums = { 7, 8, 9, 10, 11 };
        Console.WriteLine(nums.Length);
    }
}

Test yourself

Match each concept to its meaning

.Length

Element count
nums[0]

First element
nums.Length - 1

Last index
IndexOutOfRange

Out-of-range error
With int[] nums = new int[5]; what is nums.Length?
```
int[] nums = new int[5];
Console.WriteLine(nums.Length);
```
- 0
- 4
- 6
- 5
Show answer

5 — Correct. new int[5] creates a five-element array; Length is 5.

Write the .Length property

int[] nums = {1, 2, 3, 4};
int count = nums____;

Show answer

int[] nums = {1, 2, 3, 4};
int count = nums.Length;

Next lesson: Multidimensional arrays

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