Array operations (append, insert, remove) in Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the append() method do in a Swift array?

It adds a new element to the end of the array, increasing its size by one.

beginner

How do you insert an element at a specific position in a Swift array?

Use the insert(_:at:) method, specifying the element and the index where you want to add it.

beginner

What happens when you use remove(at:) on a Swift array?

It removes the element at the specified index and shifts the remaining elements to fill the gap.

beginner

If you want to remove the last element of a Swift array, which method do you use?

Use removeLast() to remove and return the last element of the array.

intermediate

Can you append multiple elements to a Swift array at once? If yes, how?

Yes, use the append(contentsOf:) method with another array or sequence of elements.

Which method adds a single element to the end of a Swift array?

A pop()

B insert()

C remove()

D append()

The append() method adds one element to the end of the array.

How do you add an element at index 2 in a Swift array named 'fruits'?

A fruits.insert("apple", at: 2)

B fruits.remove(at: 2)

C fruits.append(2)

D fruits.add(at: 2)

Use insert(_:at:) to add an element at a specific index.

What does remove(at: 0) do to an array?

A Removes the first element

B Removes the last element

C Removes all elements

D Adds an element at the start

remove(at: 0) removes the element at index 0, which is the first element.

Which method removes and returns the last element of a Swift array?

A deleteLast()

B removeFirst()

C removeLast()

D popLast()

removeLast() removes and returns the last element.

How can you add multiple elements to a Swift array at once?

A insertMultiple()

B append(contentsOf:)

C addAll()

D appendAll()

append(contentsOf:) adds multiple elements from another collection.

Explain how to add, insert, and remove elements in a Swift array with examples.

Think about how you add things to a list, put things in the middle, or take things out.

Describe the difference between append() and insert(_:at:) in Swift arrays.

One adds to the end, the other lets you choose the spot.

Practice

1. What does the append method do in a Swift array?

easy

A. Removes the last element from the array

B. Adds a new element to the end of the array

C. Inserts an element at the beginning of the array

D. Clears all elements from the array

Solution

1. Step 1: Understand the append method

   The append method adds a new element to the end of the array, increasing its size by one.

2. Step 2: Compare with other options

   Removing elements or inserting at the beginning are done by other methods, not append.

3. Final Answer:

   Adds a new element to the end of the array -> Option B

4. Quick Check:

   append = add at end [OK]

Hint: append always adds at the end of the array [OK]

Common Mistakes:

• Confusing append with insert
• Thinking append removes elements
• Assuming append adds at the start

2. Which of the following is the correct way to insert the number 10 at index 2 in a Swift array named numbers?

easy

A. numbers.insert(10, at: 2)

B. numbers.append(10, at: 2)

C. numbers.add(10, index: 2)

D. numbers.insertAt(2, 10)

Solution

1. Step 1: Recall the insert syntax in Swift

   The correct syntax is array.insert(element, at: index), so numbers.insert(10, at: 2) is correct.

2. Step 2: Check other options for syntax errors

   Options A, B, and D use incorrect method names or argument orders.

3. Final Answer:

   numbers.insert(10, at: 2) -> Option A

4. Quick Check:

   insert(element, at: index) syntax [OK]

Hint: Use insert(element, at: index) to add anywhere [OK]

Common Mistakes:

• Using append with index
• Wrong method names like add or insertAt
• Swapping argument order

3. What will be the output of the following Swift code?

var fruits = ["Apple", "Banana", "Cherry"]
fruits.append("Date")
fruits.remove(at: 1)
print(fruits)

medium

A. ["Banana", "Cherry", "Date"]

B. ["Apple", "Banana", "Cherry", "Date"]

C. ["Apple", "Cherry", "Date"]

D. ["Apple", "Date"]

Solution

1. Step 1: Append "Date" to the fruits array

   After append, fruits = ["Apple", "Banana", "Cherry", "Date"].

2. Step 2: Remove element at index 1

   Index 1 is "Banana", so removing it results in ["Apple", "Cherry", "Date"].

3. Final Answer:

   ["Apple", "Cherry", "Date"] -> Option C

4. Quick Check:

   append + remove(at: 1) = ["Apple", "Cherry", "Date"] [OK]

Hint: Append adds end; remove(at:) deletes by index [OK]

Common Mistakes:

• Removing wrong index
• Forgetting append adds element
• Confusing remove(at:) with removeLast()

4. Identify the error in this Swift code snippet:

var numbers = [1, 2, 3]
numbers.remove(at: 3)

medium

A. Cannot remove elements from an array

B. Syntax error due to missing parentheses

C. No error, code runs fine

D. Index out of range error because index 3 does not exist

Solution

1. Step 1: Check array indexes

   Array 'numbers' has indexes 0, 1, 2. Index 3 is out of range.

2. Step 2: Understand remove(at:) behavior

   Calling remove(at: 3) causes a runtime error because the index is invalid.

3. Final Answer:

   Index out of range error because index 3 does not exist -> Option D

4. Quick Check:

   remove(at:) needs valid index [OK]

Hint: Check array size before remove(at:) [OK]

Common Mistakes:

• Using invalid index without checking
• Assuming remove(at:) can remove non-existing index
• Confusing syntax errors with runtime errors

5. Given an empty Swift array var items = [String](), which sequence of operations will result in ["Pen", "Book", "Eraser"]?

hard

A. items.insert("Pen", at: 0)items.insert("Book", at: 1)items.insert("Eraser", at: 2)

B. items.append("Pen")items.insert("Book", at: 0)items.append("Eraser")

C. items.append("Pen")items.append("Book")items.insert("Eraser", at: 1)

D. items.insert("Pen", at: 1)items.append("Book")items.append("Eraser")

Solution

1. Step 1: Start with empty array and insert "Pen" at index 0

   items = ["Pen"]

2. Step 2: Insert "Book" at index 1 and "Eraser" at index 2

   items = ["Pen", "Book", "Eraser"]

3. Step 3: Check other options for correctness

   items.append("Pen")
   items.insert("Book", at: 0)
   items.append("Eraser"): append "Pen" -> ["Pen"]; insert "Book" at 0 -> ["Book", "Pen"]; append "Eraser" -> ["Book", "Pen", "Eraser"] (wrong order).
   items.append("Pen")
   items.append("Book")
   items.insert("Eraser", at: 1): append "Pen", append "Book" -> ["Pen", "Book"]; insert "Eraser" at 1 -> ["Pen", "Eraser", "Book"] (wrong order).
   items.insert("Pen", at: 1)
   items.append("Book")
   items.append("Eraser"): insert "Pen" at 1 on empty array -> index out of range error.

4. Final Answer:

   items.insert("Pen", at: 0)
   items.insert("Book", at: 1)
   items.insert("Eraser", at: 2) -> Option A

5. Quick Check:

   Insert at correct indexes builds array [OK]

Hint: Insert at indexes 0,1,2 to build array step-by-step [OK]

Common Mistakes:

• Inserting at invalid index in empty array
• Confusing append and insert order
• Assuming insert can add beyond current size