Explicit type annotation in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Swift code with explicit type annotation?

Consider the following Swift code snippet. What will be printed?

Swift

let number: Int = 5
let result = number * 2
print(result)

A Compilation error

B 5

C 10

D Type error

💡 Hint

Look at the type of number and the operation performed.

The variable number is explicitly declared as an Int. Multiplying it by 2 results in 10, which is printed.

❓ Predict Output

intermediate

What is the type of variable value here?

Given the code below, what is the type of value?

Swift

let value: Double = 3.14
print(type(of: value))

A Int

B Double

C Float

D String

💡 Hint

Check the explicit type annotation used when declaring value.

The variable value is explicitly declared as Double, so its type is Double.

🔧 Debug

advanced

Why does this Swift code cause a compilation error?

Examine the code below. Why does it fail to compile?

Swift

let text: Int = "Hello"
print(text)

A Cannot assign a String to an Int variable

B Missing semicolon at the end of the line

C Variable <code>text</code> is not initialized

D Print statement syntax is incorrect

💡 Hint

Look at the type annotation and the assigned value.

The variable text is declared as Int but assigned a String. This causes a type mismatch error.

❓ Predict Output

advanced

What is the output of this Swift code with explicit type annotation and optional?

What will this code print?

Swift

let optionalNumber: Int? = 10
if let number: Int = optionalNumber {
    print(number * 3)
} else {
    print("No value")
}

A 30

B No value

C Optional(30)

D Compilation error

💡 Hint

Check how optional binding with explicit type annotation works.

The optional optionalNumber contains 10, so number is assigned 10 and multiplied by 3, printing 30.

🧠 Conceptual

expert

Why is explicit type annotation useful in Swift?

Choose the best reason why explicit type annotation is important in Swift programming.

A It automatically converts all types to String

B It makes the code run faster at runtime

C It allows variables to change types dynamically

D It helps the compiler catch type errors early and improves code readability

💡 Hint

Think about how Swift uses types to prevent bugs.

Explicit type annotation helps the compiler detect type mismatches early and makes the code clearer for humans reading it.

Practice

1. What does explicit type annotation in Swift do?

easy

A. It removes the need to declare variables.

B. It automatically converts types during runtime.

C. It tells the exact data type of a variable or constant.

D. It makes the program run faster by skipping type checks.

Solution

1. Step 1: Understand the purpose of explicit type annotation

   Explicit type annotation is used to specify the exact data type of a variable or constant in Swift.

2. Step 2: Compare with other options

   The other options describe behaviors unrelated to explicit type annotation, such as automatic conversion, removing the need to declare variables, or performance improvements.

3. Final Answer:

   It tells the exact data type of a variable or constant. -> Option C

4. Quick Check:

   Explicit type annotation = exact data type [OK]

Hint: Explicit type annotation means writing the type after the variable name [OK]

Common Mistakes:

• Thinking it changes runtime behavior
• Confusing with type inference
• Believing it speeds up code execution

2. Which of the following is the correct syntax for explicit type annotation in Swift?

easy

A. var age: Int = 25

B. var age = Int: 25

C. var age Int = 25

D. var age = 25: Int

Solution

1. Step 1: Recall Swift syntax for explicit type annotation

   The correct syntax is to write the variable name, then a colon, then the type, then an equals sign and the value.

2. Step 2: Check each option

   var age: Int = 25 matches this syntax exactly. The other options have misplaced colons or missing punctuation.

3. Final Answer:

   var age: Int = 25 -> Option A

4. Quick Check:

   Variable name : Type = value [OK]

Hint: Remember: variableName: Type = value [OK]

Common Mistakes:

• Putting colon after the value
• Missing colon between name and type
• Using equal sign before type

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

let pi: Double = 3
print(pi)

medium

A. Error: Cannot assign Int to Double

B. 3

C. 3.00

D. 3.0

Solution

1. Step 1: Analyze the type annotation and assigned value

   The variable pi is declared as a Double but assigned the integer 3. Swift converts the integer 3 to 3.0 automatically.

2. Step 2: Understand print output for Double

   Printing a Double with value 3 prints as 3.0 by default.

3. Final Answer:

   3.0 -> Option D

4. Quick Check:

   Double 3 prints as 3.0 [OK]

Hint: Assigning Int to Double converts to decimal automatically [OK]

Common Mistakes:

• Expecting a compile error
• Thinking print shows integer 3
• Confusing Double formatting

4. Identify the error in this Swift code:

var name: String = 123
print(name)

medium

A. Type mismatch: cannot assign Int to String

B. Variable name is a reserved keyword

C. Missing explicit type annotation

D. No error, prints 123

Solution

1. Step 1: Check the declared type and assigned value

   The variable name is declared as String but assigned an integer 123, which is a type mismatch.

2. Step 2: Understand Swift's type safety

   Swift does not allow assigning an Int to a String variable, causing a compile-time error.

3. Final Answer:

   Type mismatch: cannot assign Int to String -> Option A

4. Quick Check:

   Type mismatch error = Type mismatch: cannot assign Int to String [OK]

Hint: Check if assigned value matches declared type exactly [OK]

Common Mistakes:

• Assuming implicit conversion from Int to String
• Ignoring type mismatch errors
• Thinking variable names are reserved keywords

5. You want to store a list of ages as integers but accidentally write:

var ages: [String] = [20, 25, 30]

What is the best fix using explicit type annotation?

hard

A. Change to var ages = ["20", "25", "30"]

B. Change to var ages: [Int] = [20, 25, 30]

C. Remove type annotation and write var ages = [20, 25, 30]

D. Change to var ages: Int = [20, 25, 30]

Solution

1. Step 1: Identify the mismatch between type and values

   The variable ages is declared as an array of Strings but assigned integer values, causing a type mismatch.

2. Step 2: Fix by matching type annotation to actual data

   Changing the type annotation to [Int] matches the integer values in the array.

3. Final Answer:

   var ages: [Int] = [20, 25, 30] -> Option B

4. Quick Check:

   Array type matches element types [OK]

Hint: Match array type annotation to the element types [OK]

Common Mistakes:

• Changing values to strings unnecessarily
• Removing type annotation without understanding
• Using single Int type for array