Explicit type annotation in Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is explicit type annotation in Swift?

Explicit type annotation means telling Swift exactly what type a variable or constant should be, by writing the type after the name with a colon. For example, <code>let age: Int = 30</code> means <strong>age</strong> is an integer.

beginner

Why use explicit type annotation in Swift?

You use explicit type annotation to make your code clearer, help the compiler catch mistakes early, and sometimes to fix ambiguous types when Swift can't guess the type on its own.

beginner

How do you write explicit type annotation for a variable named name that holds a string?

You write: var name: String. This tells Swift that name will always hold text data.

intermediate

What happens if you assign a value of the wrong type to a variable with explicit type annotation?

Swift will give a compile-time error because the value does not match the declared type. For example, if var age: Int and you try age = "thirty", it will not work.

beginner

Can you give an example of explicit type annotation with a constant?

Yes! For example: <code>let pi: Double = 3.14159</code> means <strong>pi</strong> is a constant of type Double (decimal number).

What does this Swift code do? var score: Int = 100

A Declares a variable named score that holds a string value

B Declares a constant named score with value 100

C Declares a variable named score that holds an integer value 100

D Declares a variable named score without a type

The code declares a variable score with explicit type Int and assigns it the value 100.

Why might you use explicit type annotation in Swift?

A To allow variables to change type later

B To make the program run faster

C To avoid writing variable names

D To make the code clearer and avoid type guessing errors

Explicit type annotation helps the compiler and readers understand exactly what type a variable or constant should have.

What error will Swift give if you write var count: Int = "five"?

A Runtime error when the program runs

B Type mismatch error because "five" is a string, not an Int

C Syntax error because of missing semicolon

D No error, Swift converts string to Int automatically

Swift enforces type safety and will not allow assigning a string to an Int variable.

Which of these is a correct explicit type annotation for a Boolean variable named isOpen?

A var isOpen: Bool = true

B var isOpen: Boolean = true

C var isOpen = true

D var isOpen: int = true

In Swift, the Boolean type is called Bool, so var isOpen: Bool = true is correct.

What does the colon (:) mean in let name: String?

A It separates the variable name from its type

B It assigns a value to the variable

C It declares a function

D It comments the code

The colon is used to specify the type of a variable or constant after its name.

Explain what explicit type annotation is and why it is useful in Swift.

Think about how you tell Swift exactly what kind of data a variable holds.

Write an example of a Swift variable with explicit type annotation and explain each part.

Try something like <code>var age: Int = 25</code> and explain it.