Function declaration syntax in Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the basic syntax to declare a function in Swift?

Use the func keyword, followed by the function name, parentheses for parameters, and curly braces for the function body.

Example:
func greet() {
print("Hello")
}

beginner

How do you declare a function in Swift that takes parameters?

Inside the parentheses, list parameters with their names and types separated by colons.

Example:
func greet(name: String) {
print("Hello, \(name)!")
}

beginner

How do you specify a return type in a Swift function declaration?

Add an arrow -> followed by the return type after the parameter list.

Example:
func add(a: Int, b: Int) -> Int {
return a + b
}

beginner

What keyword do you use to return a value from a Swift function?

Use the return keyword followed by the value you want to send back.

Example:
func square(number: Int) -> Int {
return number * number
}

beginner

Can Swift functions have no parameters and no return value? How?

Yes, simply declare the function with empty parentheses and no return type.

Example:
func sayHello() {
print("Hello!")
}

Which keyword starts a function declaration in Swift?

A def

B function

C func

D fun

Swift uses func to declare functions.

How do you declare a function that returns an integer in Swift?

A func example() -> Int {}

B func example(): Int {}

C func example() returns Int {}

D func example() Int {}

The return type is specified with -> Type after the parameter list.

What symbol separates parameter names and their types in Swift function declarations?

A ,

B =

C ->

D :

Parameters are declared as name: Type.

Which keyword is used to send a value back from a Swift function?

A return

B yield

C send

D output

Use return to output a value from a function.

Can a Swift function have no parameters and no return type?

A Yes, but only if marked with special keyword

B Yes, by using empty parentheses and no return arrow

C No, functions must return a value

D No, functions must have parameters

Functions can have empty parentheses and no return type.

Explain how to declare a function in Swift that takes two integers and returns their sum.

Think about the function name, parameters, return type, and how to return the result.

Describe the parts of a Swift function declaration and their purpose.

Consider what each part does in the function.

Practice

1. Which keyword is used to declare a function in Swift?

easy

A. def

B. func

C. function

D. method

Solution

1. Step 1: Recall Swift function declaration

   In Swift, functions always start with the keyword func.

2. Step 2: Compare options

   Only func uses func, the correct keyword for Swift functions.

3. Final Answer:

   func -> Option B

4. Quick Check:

   Swift functions start with func [OK]

Hint: Remember: Swift functions always start with 'func' keyword [OK]

Common Mistakes:

• Using 'function' instead of 'func'
• Confusing Swift with Python's 'def'
• Using 'method' which is not a keyword

2. Which of the following is the correct syntax to declare a function named greet that takes no parameters and returns nothing?

easy

A. func greet() -> void {}

B. function greet() {}

C. func greet {}

D. func greet() {}

Solution

1. Step 1: Check function declaration syntax

   In Swift, a function with no parameters and no return type is declared as func name() {}.

2. Step 2: Analyze each option

   func greet() {} matches the correct syntax. function greet() {} uses 'function' which is invalid. func greet {} misses parentheses. func greet() -> void {} uses 'void' which is not used in Swift.

3. Final Answer:

   func greet() {} -> Option D

4. Quick Check:

   Empty parameter list needs () and no return type means no arrow [OK]

Hint: Empty parameters always need () after function name [OK]

Common Mistakes:

• Omitting parentheses for parameters
• Using 'function' instead of 'func'
• Using 'void' as return type in Swift

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

func add(a: Int, b: Int) -> Int {
    return a + b
}

print(add(a: 3, b: 4))

medium

A. a + b

B. 34

C. 7

D. Error: Missing return statement

Solution

1. Step 1: Understand function parameters and return

   The function add takes two integers and returns their sum.

2. Step 2: Calculate the function call result

   Calling add(a: 3, b: 4) returns 3 + 4 = 7, which is printed.

3. Final Answer:

   7 -> Option C

4. Quick Check:

   Sum of 3 and 4 is 7 [OK]

Hint: Add numbers inside function and print result [OK]

Common Mistakes:

• Concatenating numbers as strings
• Forgetting to return a value
• Misunderstanding parameter labels

4. Identify the error in the following Swift function declaration:

func multiply(a: Int, b Int) -> Int {
    return a * b
}

medium

A. Missing colon between parameter name and type for b

B. Missing return keyword

C. Function name is invalid

D. Return type should be String

Solution

1. Step 1: Check parameter syntax

   Each parameter must have a colon between its name and type. Here, b Int is missing a colon.

2. Step 2: Confirm other parts are correct

   The return keyword is present, function name is valid, and return type Int is appropriate.

3. Final Answer:

   Missing colon between parameter name and type for b -> Option A

4. Quick Check:

   Parameters need colon between name and type [OK]

Hint: Check colons between parameter names and types [OK]

Common Mistakes:

• Omitting colon in parameter list
• Forgetting return keyword
• Using wrong return type

5. You want to declare a Swift function named describePerson that takes a String parameter name and an Int parameter age, and returns a String describing the person like "Name is Age years old." Which is the correct function declaration?

hard

A. func describePerson(name: String, age: Int) -> String {
return "\(name) is \(age) years old."
}

B. func describePerson(name String, age Int) -> String {
return "\(name) is \(age) years old."
}

C. func describePerson(name: String, age: Int) {
print("\(name) is \(age) years old.")
}

D. func describePerson(name: String, age: Int) -> Void {
return "\(name) is \(age) years old."
}

Solution

1. Step 1: Check parameter syntax and return type

   Parameters must have colons between name and type. The function returns a String, so return type must be String.

2. Step 2: Verify function body matches return type

   func describePerson(name: String, age: Int) -> String { return "\(name) is \(age) years old." } returns a String with correct string interpolation. func describePerson(name String, age Int) -> String { return "\(name) is \(age) years old." } misses colons. func describePerson(name: String, age: Int) { print("\(name) is \(age) years old.") } has no return type and uses print instead of return. func describePerson(name: String, age: Int) -> Void { return "\(name) is \(age) years old." } uses Void return type but returns a String, which is invalid.

3. Final Answer:

   func describePerson(name: String, age: Int) -> String { return "\(name) is \(age) years old." } -> Option A

4. Quick Check:

   Correct parameters and return type with string interpolation [OK]

Hint: Use colons for parameters and match return type with returned value [OK]

Common Mistakes:

• Omitting colons in parameters
• Using print instead of return for returning values
• Mismatching return type and returned value