Object arrays in PowerShell - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of creating and accessing object arrays

What is the output of this PowerShell script?

PowerShell

$arr = @()
$arr += [PSCustomObject]@{Name='Alice'; Age=30}
$arr += [PSCustomObject]@{Name='Bob'; Age=25}
$arr[1].Name

A 30

B Alice

C 25

D Bob

💡 Hint

Remember arrays start at index 0.

The array has two objects. Index 1 is the second object with Name 'Bob'.

📝 Syntax

intermediate

Correct syntax to create an array of objects

Which option correctly creates an array of two objects with properties Name and Age?

A $arr = @([PSCustomObject]([Name='Tom'; Age=40]), [PSCustomObject]([Name='Jerry'; Age=35]))

B $arr = @([PSCustomObject]@{Name='Tom'; Age=40}, [PSCustomObject]@{Name='Jerry'; Age=35})

C $arr = @([PSCustomObject]{Name='Tom'; Age=40}, [PSCustomObject]{Name='Jerry'; Age=35})

D $arr = [PSCustomObject]@{Name='Tom'; Age=40}, [PSCustomObject]@{Name='Jerry'; Age=35}

💡 Hint

Use @() to create an array and @{} to create objects.

Option B correctly uses @() for array and [PSCustomObject]@{} for objects.

🔧 Debug

advanced

Identify the error in adding objects to an array

What error does this script produce? $arr = @() $arr += @{Name='Anna'; Age=28} $arr[0].Name

A No error, outputs 'Anna'

B Runtime error: Cannot index into a null array

C Runtime error: Property 'Name' not found

D Syntax error: Missing [PSCustomObject]

💡 Hint

Check the type of object added to the array.

The script adds a hashtable, not a PSCustomObject, so accessing .Name fails.

🚀 Application

advanced

Filter object array by property value

Given an array of objects with property Age, which command returns only objects where Age is greater than 30?

A $arr | Where-Object { $_.Age -gt 30 }

B $arr | Where-Object Age > 30

C $arr | Where { Age -gt 30 }

D $arr | Filter-Object { $_.Age -gt 30 }

💡 Hint

Use Where-Object with a script block and $_ for current object.

Option A uses correct syntax with Where-Object and $_ to filter by Age.

🧠 Conceptual

expert

Understanding object array property modification

If you modify a property of an object inside a PowerShell array, what happens to the array?

A The array updates because objects are referenced, so changes reflect in the array.

B The array remains unchanged because objects are copied when added.

C The array throws an error because objects are immutable.

D The array duplicates the object with the new property value.

💡 Hint

Think about how PowerShell handles objects in arrays.

PowerShell arrays hold references to objects, so modifying an object changes it inside the array.

Practice

1. What is an object array in PowerShell?

easy

A. A type of function that returns objects

B. A single object with many properties

C. A command to create new objects

D. A variable that holds multiple objects together in a list

Solution

1. Step 1: Understand the definition of object arrays

   An object array is a collection that holds many objects in one variable, like a list.

2. Step 2: Compare options with the definition

   Only A variable that holds multiple objects together in a list correctly describes an object array as a variable holding multiple objects.

3. Final Answer:

   A variable that holds multiple objects together in a list -> Option D

4. Quick Check:

   Object array = list of objects [OK]

Hint: Remember: arrays hold many items together [OK]

Common Mistakes:

• Confusing object arrays with single objects
• Thinking object arrays are commands
• Mixing arrays with functions

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

easy

A. $array = ()

B. $array = @()

C. $array = new-object array

D. $array = {}

Solution

1. Step 1: Recall PowerShell syntax for empty arrays

   PowerShell uses @() to create an empty array.

2. Step 2: Check each option

   $array = @() uses @(), which is correct. $array = () uses (), which assigns $null, not an array. $array = new-object array is incorrect syntax. $array = {} uses {}, which creates a hashtable, not an array.

3. Final Answer:

   $array = @() -> Option B

4. Quick Check:

   Empty array syntax = @() [OK]

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

Common Mistakes:

• Using () which assigns null, not an array
• Confusing arrays with hashtables {}
• Trying to use new-object for arrays

3. What will be the output of this PowerShell code?

$array = @()
$array += 'apple'
$array += 'banana'
$array += 'cherry'
$array

medium

A. apple
banana
cherry

B. @('apple', 'banana', 'cherry')

C. apple banana cherry

D. Error: Cannot add to array

Solution

1. Step 1: Understand how += adds items to arrays

   Using += adds each string as a new element to the array.

2. Step 2: Output the array variable

   When output, PowerShell prints each element on a new line, so the output is three lines: apple, banana, cherry.

3. Final Answer:

   apple banana cherry -> Option A

4. Quick Check:

   Array elements print line by line [OK]

Hint: Arrays print each item on its own line [OK]

Common Mistakes:

• Expecting all items on one line separated by spaces
• Thinking += causes an error on arrays
• Confusing array output with string output

4. Identify the error in this PowerShell script:

$array = @()
$array += 'one'
$array = $array + 'two'
$array = $array + 3
$array

medium

A. No error; script runs and outputs all items

B. Using + operator on arrays causes error

C. Cannot add integer to string array

D. Array must be declared with fixed size

Solution

1. Step 1: Check adding different types to array

   PowerShell arrays can hold mixed types, so adding integer 3 is allowed.

2. Step 2: Check use of + operator on arrays

   Using + concatenates arrays or adds items; it works fine here.

3. Final Answer:

   No error; script runs and outputs all items -> Option A

4. Quick Check:

   PowerShell arrays accept mixed types and + works [OK]

Hint: PowerShell arrays can mix types and use + to add items [OK]

Common Mistakes:

• Thinking arrays only hold one data type
• Believing + operator causes errors on arrays
• Assuming arrays need fixed size

5. You have an array of objects representing people:

$people = @(
  [pscustomobject]@{Name='Alice'; Age=30},
  [pscustomobject]@{Name='Bob'; Age=25},
  [pscustomobject]@{Name='Carol'; Age=35}
)

How do you add a new person object with Name='Dave' and Age=40 to this array?

hard

A. $people = @($people, @{Name='Dave'; Age=40})

B. $people = $people + @{Name='Dave'; Age=40}

C. $people += [pscustomobject]@{Name='Dave'; Age=40}

D. $people.Add([pscustomobject]@{Name='Dave'; Age=40})

Solution

1. Step 1: Create a new person object correctly

   Use [pscustomobject]@{Name='Dave'; Age=40} to create the new object.

2. Step 2: Add the new object to the existing array

   Use += to add the new object to the $people array. $people += [pscustomobject]@{Name='Dave'; Age=40} does this correctly.

3. Final Answer:

   $people += [pscustomobject]@{Name='Dave'; Age=40} -> Option C

4. Quick Check:

   Add object to array using += [OK]

Hint: Use += with new [pscustomobject] to add to array [OK]

Common Mistakes:

• Forgetting [pscustomobject] and adding plain hashtable
• Using .Add() which does not work on arrays
• Reassigning array incorrectly causing nested arrays