Variables (let, var) and type inference in iOS Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

📝 Syntax

intermediate

What is the output of this Swift code snippet?

Consider the following Swift code:

let x = 10
var y = 5
y = y + x
print(y)

What will be printed?

iOS Swift

let x = 10
var y = 5
y = y + x
print(y)

A 10

B 15

C 5

D Compilation error

💡 Hint

Remember that 'let' defines a constant and 'var' defines a variable that can change.

The variable y starts at 5, then we add x (which is 10) to y, so y becomes 15. The print statement outputs 15.

❓ ui_behavior

intermediate

What happens if you try to change a 'let' constant in Swift?

Given this code:

let name = "Alice"
name = "Bob"

What will happen when you try to compile this?

iOS Swift

let name = "Alice"
name = "Bob"

A Runtime error when assigning "Bob"

B The value of 'name' changes to "Bob"

C Compilation error because 'name' is a constant

D The code runs but prints "Alice"

💡 Hint

Think about what 'let' means in Swift.

'let' declares a constant, so you cannot assign a new value after initialization. The compiler will show an error.

🧠 Conceptual

advanced

What type does Swift infer for this variable?

Look at this Swift code:

var score = 42

What type does Swift assign to 'score'?

iOS Swift

var score = 42

A Int

B Double

C String

D Any

💡 Hint

Swift infers types based on the assigned value.

Since 42 is an integer literal, Swift infers the type of 'score' as Int.

❓ lifecycle

advanced

What is the value of 'message' after this code runs?

Consider this Swift code:

var message = "Hello"
let greeting = message
message = "Hi"
print(greeting)

What will be printed?

iOS Swift

var message = "Hello"
let greeting = message
message = "Hi"
print(greeting)

A Hello

B Hi

C Compilation error

D Runtime error

💡 Hint

Think about how assignment copies values for strings in Swift.

The constant 'greeting' copies the value of 'message' at assignment time, so it remains "Hello" even after 'message' changes.

🔧 Debug

expert

Which option causes a compile-time error?

Which of these Swift code snippets will NOT compile?

A

var text = "Hello"
text = "World"

B let pi = 3.14

C

var flag: Bool
flag = true

D

let number: Int = 10
number = 20

💡 Hint

Remember that 'let' constants cannot be reassigned.

Option D tries to assign a new value to a constant 'number', which causes a compile-time error.