Arrays in PowerShell - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an array in PowerShell?

An array in PowerShell is a collection of items stored in a single variable. It can hold multiple values like numbers, strings, or objects, all together.

beginner

How do you create an array with three numbers: 5, 10, and 15?

You create it by listing the values inside @() like this:
$numbers = @(5, 10, 15)

beginner

How do you access the second item in an array named $colors?

Use the index number inside square brackets. Remember, counting starts at 0. So, the second item is $colors[1].

intermediate

How can you add an item to an existing array in PowerShell?

Arrays are fixed size, but you can create a new array by adding items like this:
$newArray = $oldArray + 'newItem'

beginner

What happens if you try to access an index that does not exist in an array?

PowerShell returns nothing (null) without an error. It just gives an empty result.

How do you create an empty array in PowerShell?

A $array = ''

B $array = @()

C $array = {}

D $array = []

In PowerShell, an empty array is created with @() syntax.

What is the index of the first element in a PowerShell array?

A 1

B -1

C 0

D It depends on the array

PowerShell arrays start counting at 0, so the first element is at index 0.

Which of these adds an item 'apple' to an existing array $fruits?

A $fruits += 'apple'

B Neither A nor C

C $fruits = $fruits + 'apple'

D Both A and C

Both += and + create a new array with the added item in PowerShell.

What will $array[10] return if $array has only 5 items?

A Null or empty

B An error

C The last item

D The first item

Accessing an index outside the array returns null or empty without error.

How do you find the number of items in an array $items?

A Both B and C

B $items.Count

C $items.Length

D $items.Size

PowerShell arrays support both .Length and .Count properties to get the number of items.

Explain how to create, access, and add items to an array in PowerShell.

Think about how you store a list of things and get or add items.

What happens if you try to get an array item at an index that does not exist? How does PowerShell handle it?

Imagine asking for a seat number that is not in the theater.

Practice

1. What does an array in PowerShell do?

easy

A. Stores only one item at a time

B. Stores multiple items in one variable

C. Runs commands sequentially

D. Creates a new script file

Solution

1. Step 1: Understand the purpose of arrays

   Arrays hold multiple values together in one variable, unlike single variables that hold one value.

2. Step 2: Compare options with array definition

   Only Stores multiple items in one variable correctly describes storing multiple items in one variable, which matches the array concept.

3. Final Answer:

   Stores multiple items in one variable -> Option B

4. Quick Check:

   Arrays = store multiple items [OK]

Hint: Arrays hold many items together in one variable [OK]

Common Mistakes:

• Thinking arrays hold only one item
• Confusing arrays with scripts or commands
• Believing arrays create files

2. Which of the following is the correct way to create an empty array in PowerShell?

easy

A. $arr = []

B. $arr = array()

C. $arr = {}

D. $arr = @()

Solution

1. Step 1: Recall PowerShell array syntax

   PowerShell uses @() to create arrays, including empty ones.

2. Step 2: Check each option

   $arr = @() uses @() which is correct. Options A, B, and C use invalid or different syntax for arrays.

3. Final Answer:

   $arr = @() -> Option D

4. Quick Check:

   Empty array = @() [OK]

Hint: Use @() to create arrays in PowerShell [OK]

Common Mistakes:

• Using [] which is not valid for arrays in PowerShell
• Using {} which is for hashtables or script blocks
• Using array() which is not recognized in PowerShell

3. What is the output of this PowerShell code?

$arr = @('apple', 'banana', 'cherry')
Write-Output $arr[1]

medium

A. banana

B. apple

C. cherry

D. 1

Solution

1. Step 1: Understand array indexing in PowerShell

   Arrays start at index 0, so $arr[0] = 'apple', $arr[1] = 'banana', $arr[2] = 'cherry'.

2. Step 2: Identify the output of $arr[1]

   The code outputs the item at index 1, which is 'banana'.

3. Final Answer:

   banana -> Option A

4. Quick Check:

   Index 1 = banana [OK]

Hint: Arrays start at zero; index 1 is second item [OK]

Common Mistakes:

• Thinking index starts at 1
• Confusing item values with index numbers
• Expecting all items printed instead of one

4. Identify the error in this PowerShell code:

$arr = @()
$arr + 'orange'

medium

A. += operator is missing to add item

B. Array cannot be empty

C. Use [] instead of @() for arrays

D. Variable name must start with capital letter

Solution

1. Step 1: Check how to add items to arrays

   In PowerShell, to add an item to an array, use '+=' operator, not just '+'.

2. Step 2: Analyze the code

   The code uses '$arr + 'orange'' which does not update $arr. It should be '$arr += 'orange'' to add the item.

3. Final Answer:

   += operator is missing to add item -> Option A

4. Quick Check:

   Add item with += [OK]

Hint: Use += to add items to arrays, not just + [OK]

Common Mistakes:

• Using + without = to add items
• Thinking arrays cannot be empty
• Confusing array syntax with other languages

5. You have an array $arr = @('cat', 'dog', 'bird'). How do you add 'fish' to the end and then print all items one per line?

hard

A. $arr = $arr + 'fish'; Write-Host $arr

B. $arr + 'fish'; Write-Output $arr

C. $arr += 'fish'; $arr | ForEach-Object { Write-Output $_ }

D. $arr += 'fish'; Write-Host $arr[0], $arr[1], $arr[2], $arr[3]

Solution

1. Step 1: Add 'fish' to the array correctly

   Use '+=' operator to add 'fish' to $arr: $arr += 'fish'.

2. Step 2: Print each item on its own line

   Use pipeline with ForEach-Object and Write-Output to print each item separately.

3. Step 3: Check each option

   $arr += 'fish'; $arr | ForEach-Object { Write-Output $_ } correctly adds and prints items line by line. $arr + 'fish'; Write-Output $arr does not update $arr. $arr = $arr + 'fish'; Write-Host $arr uses Write-Host which prints all items on one line. $arr += 'fish'; Write-Host $arr[0], $arr[1], $arr[2], $arr[3] prints items but manually and is less flexible.

4. Final Answer:

   $arr += 'fish'; $arr | ForEach-Object { Write-Output $_ } -> Option C

5. Quick Check:

   Add with += and print with pipeline [OK]

Hint: Add with += and print each item using pipeline [OK]

Common Mistakes:

• Using + without = to add items
• Printing array without pipeline for separate lines
• Using Write-Host which prints all on one line