Data types (Int, Double, String, Bool) in iOS Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

📝 Syntax

intermediate

Swift Data Type Declaration

What is the output of this Swift code snippet?

iOS Swift

let number: Int = 10
let price: Double = 9.99
let name: String = "Coffee"
let isAvailable: Bool = true
print("\(name) costs \(price) and availability is \(isAvailable)")

A Coffee costs 9.99 and availability is True

B Coffee costs 9.99 and availability is 1

C Coffee costs 9.99 and availability is true

D Coffee costs 9.99 and availability is Yes

💡 Hint

Remember how Swift prints Boolean values in strings.

In Swift, Bool values print as 'true' or 'false' in lowercase when interpolated in strings.

❓ ui_behavior

intermediate

Displaying Different Data Types in UILabel

You want to show an integer, a double, and a boolean in a UILabel in Swift. Which code snippet correctly converts all values to a string for display?

A label.text = "Int: " + String(intValue) + ", Double: " + String(doubleValue) + ", Bool: " + String(boolValue)

B label.text = String(intValue) + String(doubleValue) + String(boolValue)

C label.text = "Int: \(intValue), Double: \(doubleValue), Bool: \(boolValue)"

D label.text = "Int: " + intValue + ", Double: " + doubleValue + ", Bool: " + boolValue

💡 Hint

You cannot add non-string types directly to strings in Swift.

In Swift, you must convert non-string types to String before concatenation with + operator. String interpolation (option A) also works but option A explicitly converts each value.

🧠 Conceptual

advanced

Type Safety in Swift

Which statement best describes Swift's type safety with Int, Double, String, and Bool?

A Swift automatically converts String to Int if the string contains digits.

B Swift requires explicit conversion between Int and Double to avoid type errors.

C Swift treats Bool as a subtype of Int, so they can be used interchangeably.

D Swift allows implicit conversion between Int and Double without errors.

💡 Hint

Think about how Swift handles different numeric types.

Swift is strongly typed and does not allow implicit conversion between Int and Double. You must convert explicitly using initializers like Double(intValue).

❓ lifecycle

advanced

Variable Initialization and Default Values

What is the default value of an uninitialized variable of type Bool in Swift?

A true

B false

C nil

D Swift does not allow uninitialized variables; it causes a compile error

💡 Hint

Swift enforces initialization before use.

Swift requires all variables to be initialized before use. Declaring a variable without initialization causes a compile-time error.

🔧 Debug

expert

Debugging Type Mismatch Error

What error will this Swift code produce? let value: Int = 5 let result: Double = value print(result)

iOS Swift

let value: Int = 5
let result: Double = value
print(result)

A Type mismatch error: Cannot assign Int to Double without conversion

B Prints 5.0 without error

C Runtime error: Cannot convert Int to Double

D Syntax error: Missing semicolon

💡 Hint

Check how Swift handles assigning Int to Double variables.

Swift does not implicitly convert Int to Double. You must explicitly convert using Double(value).

Practice

1. Which Swift data type is used to store true or false values?

easy

A. Int

B. Double

C. String

D. Bool

Solution

1. Step 1: Understand the data types

   Bool stores true or false values, Int stores whole numbers, String stores text, and Double stores decimal numbers.

2. Step 2: Match the description to the type

   Since the question asks for true or false values, the correct type is Bool.

3. Final Answer:

   Bool -> Option D

4. Quick Check:

   Bool = true/false [OK]

Hint: True/false values always use Bool type [OK]

Common Mistakes:

• Confusing Bool with Int
• Using String for true/false
• Choosing Double for boolean values

2. Which of the following is the correct way to declare a Double variable named price with value 9.99 in Swift?

easy

A. var price: Double = 9.99

B. var price = "9.99"

C. var price Double = 9.99

D. var price: Int = 9.99

Solution

1. Step 1: Check variable declaration syntax

   In Swift, to declare a variable with a specific type, use var name: Type = value.

2. Step 2: Identify the correct type and value

   Since 9.99 is a decimal number, the type must be Double. var price: Double = 9.99 correctly declares price as Double with 9.99.

3. Final Answer:

   var price: Double = 9.99 -> Option A

4. Quick Check:

   Double declaration uses var name: Double = value [OK]

Hint: Use var name: Double = value for decimals [OK]

Common Mistakes:

• Assigning decimal to Int
• Using quotes for numbers
• Omitting type when needed

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

let number: Int = 5
let text: String = "5"
let isEqual = (number == Int(text)!)
print(isEqual)

medium

A. true

B. false

C. 5

D. Compilation error

Solution

1. Step 1: Understand the code logic

   number is an Int with value 5, text is a String "5". Int(text) converts the string "5" to integer 5.

2. Step 2: Compare values

   number == Int(text) compares 5 == 5, which is true. So isEqual is true and print outputs true.

3. Final Answer:

   true -> Option A

4. Quick Check:

   5 == 5 is true [OK]

Hint: Convert String to Int before comparing [OK]

Common Mistakes:

• Comparing Int and String directly
• Forgetting Int(text) conversion
• Expecting string output

4. Identify the error in this Swift code snippet:

var isActive: Bool = "true"
print(isActive)

medium

A. print() cannot print Bool values

B. Bool cannot be assigned a String value

C. Variable name is invalid

D. Missing semicolon at end of line

Solution

1. Step 1: Analyze variable assignment

   isActive is declared as Bool but assigned the string "true" (in quotes), which is incorrect.

2. Step 2: Understand type mismatch

   Bool must be assigned true or false without quotes. Assigning a String causes a type error.

3. Final Answer:

   Bool cannot be assigned a String value -> Option B

4. Quick Check:

   Bool = true/false only, no quotes [OK]

Hint: Bool values are true or false without quotes [OK]

Common Mistakes:

• Using quotes around true/false
• Expecting semicolon error
• Thinking print can't show Bool

5. You want to store a user's age, height in meters, full name, and whether they are a student. Which Swift data types should you use for these variables respectively?

hard

A. String, String, Int, Bool

B. Double, Int, Bool, String

C. Int, Double, String, Bool

D. Bool, Int, Double, String

Solution

1. Step 1: Match each data to its type

   Age is a whole number -> Int, height with decimals -> Double, full name is text -> String, student status true/false -> Bool.

2. Step 2: Verify option matches order

   Int, Double, String, Bool lists Int, Double, String, Bool in that order, matching the variables correctly.

3. Final Answer:

   Int, Double, String, Bool -> Option C

4. Quick Check:

   Whole number, decimal, text, true/false [OK]

Hint: Match data meaning: whole, decimal, text, true/false [OK]

Common Mistakes:

• Mixing Int and Double
• Using Bool for text
• Confusing order of types