Array operations (append, insert, remove) in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Swift code?

Consider the following Swift code that modifies an array. What will be printed?

Swift

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

A ["Apple", "Banana", "Elderberry", "Cherry", "Date"]

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

C ["Apple", "Banana", "Cherry", "Date", "Elderberry"]

D ["Elderberry", "Apple", "Banana", "Cherry", "Date"]

💡 Hint

Remember that insert(at:) adds the element at the specified index, shifting others to the right.

The array starts as ["Apple", "Banana", "Cherry"]. append("Date") adds "Date" at the end. insert("Elderberry", at: 1) inserts "Elderberry" at index 1, pushing "Banana" and others right. So the final array is ["Apple", "Elderberry", "Banana", "Cherry", "Date"].

❓ Predict Output

intermediate

What happens after removing an element?

Given this Swift code, what will be the output?

Swift

var numbers = [10, 20, 30, 40, 50]
numbers.remove(at: 2)
print(numbers)

A [10, 20, 40, 50]

B [10, 20, 30, 40]

C [10, 30, 40, 50]

D [20, 30, 40, 50]

💡 Hint

Remember that remove(at:) removes the element at the given index and shifts the rest left.

The element at index 2 is 30. Removing it leaves [10, 20, 40, 50].

🔧 Debug

advanced

Why does this Swift code cause a runtime error?

Examine the code below. Why does it crash when run?

Swift

var letters = ["a", "b", "c"]
letters.remove(at: 3)
print(letters)

A It prints ["a", "b", "c"] without changes.

B It causes a compile-time error because remove(at:) is not a valid method.

C It causes a runtime error because index 3 is out of range for the array.

D It removes the last element "c" and prints ["a", "b"]

💡 Hint

Check the valid indices for the array before removing.

The array has indices 0, 1, 2. Trying to remove at index 3 causes a runtime 'index out of range' error.

❓ Predict Output

advanced

What is the final array after multiple operations?

What will be the output of this Swift code?

Swift

var colors = ["Red", "Green", "Blue"]
colors.insert("Yellow", at: 0)
colors.append("Purple")
colors.remove(at: 2)
print(colors)

A ["Yellow", "Red", "Blue", "Purple"]

B ["Yellow", "Red", "Green", "Purple"]

C ["Red", "Green", "Purple"]

D ["Yellow", "Green", "Blue", "Purple"]

💡 Hint

Track each operation step-by-step on the array.

Start: ["Red", "Green", "Blue"] Insert "Yellow" at 0: ["Yellow", "Red", "Green", "Blue"] Append "Purple": ["Yellow", "Red", "Green", "Blue", "Purple"] Remove at 2 ("Green"): ["Yellow", "Red", "Blue", "Purple"] Option A matches this exactly. So correct answer is B.

🧠 Conceptual

expert

How many elements remain after these operations?

Given this Swift code, how many elements are in the array after all operations?

Swift

var items = ["Pen", "Pencil", "Eraser", "Sharpener"]
items.append("Marker")
items.remove(at: 1)
items.insert("Notebook", at: 2)
items.removeLast()

A 6

B 5

C 3

D 4

💡 Hint

Count carefully after each operation.

Start with 4 elements. append("Marker") adds 1 → 5 elements. remove(at: 1) removes 1 → 4 elements. insert("Notebook", at: 2) adds 1 → 5 elements. removeLast() removes 1 → 4 elements remain.

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