What is Swift - Practice Questions & Exercises

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is Swift primarily used for?

Swift is a programming language created by Apple. What is its main use?

A Building iOS, macOS, watchOS, and tvOS apps

B Creating Android applications

C Developing Windows desktop software

D Writing server-side scripts only

💡 Hint

Think about which devices Apple makes and what language they promote for app development.

Swift is designed by Apple to build apps for their platforms like iPhone, Mac, Apple Watch, and Apple TV.

❓ Predict Output

intermediate

What is the output of this Swift code?

Look at this Swift code and choose the output it produces.

Swift

let greeting = "Hello"
let name = "Sam"
print("\(greeting), \(name)!")

A Error: Cannot print variables this way

B greeting, name!

C Hello, Sam!

D Hello name!

💡 Hint

Check how variables are inserted inside strings in Swift.

Using \(variable) inside a string inserts the variable's value. So it prints 'Hello, Sam!'.

❓ Predict Output

advanced

What does this Swift code print?

Analyze the code and select the output it produces.

Swift

var numbers = [1, 2, 3, 4, 5]
let doubled = numbers.map { $0 * 2 }
print(doubled)

A Error: map function not found

B [1, 2, 3, 4, 5]

C [1, 4, 9, 16, 25]

D [2, 4, 6, 8, 10]

💡 Hint

Remember that map applies a function to each item in the array.

The map function multiplies each number by 2, so the output is [2, 4, 6, 8, 10].

🔧 Debug

advanced

What error does this Swift code raise?

Find the error in this Swift code snippet.

Swift

let number: Int = "123"
print(number)

A Type mismatch error

B Syntax error: missing semicolon

C No error, prints 123

D Runtime error: nil value

💡 Hint

Check if the type on the left matches the value on the right.

You cannot assign a String value to an Int variable directly in Swift. This causes a type mismatch error.

🧠 Conceptual

expert

Which feature makes Swift safe and fast?

Swift is known for safety and speed. Which feature helps achieve this?

A Using dynamic typing for flexibility

B Optionals to handle absence of values safely

C Manual memory management like in C

D No type checking at compile time

💡 Hint

Think about how Swift avoids crashes from missing values.

Optionals let Swift safely handle missing or nil values, preventing many common errors and improving safety.

Practice

1. What is Swift primarily used for?

easy

A. Designing graphics

B. Building websites

C. Creating apps for Apple devices

D. Managing databases

Solution

1. Step 1: Understand Swift's main purpose

   Swift is designed mainly for developing software on Apple platforms like iPhone and Mac.

2. Step 2: Compare options with Swift's use

   Only Creating apps for Apple devices matches this use; others relate to different fields.

3. Final Answer:

   Creating apps for Apple devices -> Option C

4. Quick Check:

   Swift = Apple app development [OK]

Hint: Swift is Apple's language for apps [OK]

Common Mistakes:

• Thinking Swift is for websites
• Confusing Swift with database tools
• Assuming Swift is for graphic design

2. Which of the following is the correct way to declare a variable in Swift?

easy

A. var name = "John"

B. variable name = "John"

C. let name := "John"

D. dim name = "John"

Solution

1. Step 1: Recall Swift variable declaration syntax

   Swift uses 'var' to declare variables and '=' to assign values.

2. Step 2: Check each option

   var name = "John" matches Swift syntax; others use incorrect keywords or symbols.

3. Final Answer:

   var name = "John" -> Option A

4. Quick Check:

   Variable declaration = var name = value [OK]

Hint: Use 'var' to declare variables in Swift [OK]

Common Mistakes:

• Using 'variable' instead of 'var'
• Using ':=' instead of '='
• Using 'dim' from other languages

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

let speed = 60
let time = 2
let distance = speed * time
print(distance)

medium

A. 120

B. 62

C. Error

D. 60

Solution

1. Step 1: Calculate the multiplication

   speed (60) multiplied by time (2) equals 120.

2. Step 2: Understand print output

   The print statement outputs the value of distance, which is 120.

3. Final Answer:

   120 -> Option A

4. Quick Check:

   60 * 2 = 120 [OK]

Hint: Multiply variables and print result [OK]

Common Mistakes:

• Adding instead of multiplying
• Confusing variable names
• Expecting syntax error

4. Identify the error in this Swift code:

let age = 25
age = 30
print(age)

medium

A. Missing semicolon after print statement

B. Cannot assign a new value to a constant

C. Variable 'age' is not declared

D. Print statement syntax is incorrect

Solution

1. Step 1: Check variable declaration

   'age' is declared with 'let', making it a constant that cannot change.

2. Step 2: Identify assignment error

   Trying to assign 30 to 'age' causes an error because constants cannot be reassigned.

3. Final Answer:

   Cannot assign a new value to a constant -> Option B

4. Quick Check:

   let means constant, no reassignment [OK]

Hint: 'let' means constant, no change allowed [OK]

Common Mistakes:

• Thinking 'let' allows reassignment
• Expecting semicolons in Swift
• Misreading print syntax

5. You want to write a Swift program that safely calculates the average of an array of numbers, but the array might be empty. Which approach best uses Swift's safety features?

hard

A. Force unwrap the array count and sum

B. Divide the sum by the array count without checks

C. Ignore empty arrays and return zero always

D. Use optional binding to check if the array is empty before dividing

Solution

1. Step 1: Understand the problem with empty arrays

   Dividing by zero (array count 0) causes a runtime error.

2. Step 2: Use optional binding for safety

   Optional binding lets you check if the array has elements before dividing, avoiding errors.

3. Step 3: Evaluate options

   Use optional binding to check if the array is empty before dividing uses Swift's safety features correctly; others risk errors or ignore safety.

4. Final Answer:

   Use optional binding to check if the array is empty before dividing -> Option D

5. Quick Check:

   Optional binding = safe checks [OK]

Hint: Check array emptiness with optional binding before dividing [OK]

Common Mistakes:

• Dividing without checking for zero count
• Force unwrapping optionals causing crashes
• Ignoring empty arrays without handling