Function declaration in Go - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a function declaration in Go?

A function declaration in Go defines a reusable block of code with a name, optional parameters, and an optional return type. It tells the program what the function does when called.

beginner

How do you declare a simple function named greet that prints "Hello" in Go?

You write:

func greet() {
    fmt.Println("Hello")
}

This declares a function named greet with no parameters and no return value.

intermediate

What is the syntax to declare a function with parameters in Go?

You list parameters inside parentheses after the function name, each with a name and type. For example:

func add(a int, b int) int {
    return a + b
}

This function takes two integers and returns an integer.

intermediate

Can a Go function return multiple values? How?

Yes, Go functions can return multiple values by listing return types in parentheses. Example:

func swap(x, y string) (string, string) {
    return y, x
}

This function returns two strings.

beginner

What keyword starts a function declaration in Go?

The keyword func starts every function declaration in Go. It signals that a function is being defined.

Which keyword is used to declare a function in Go?

A func

B function

C def

D fun

In Go, the keyword func is used to declare functions.

How do you declare a function named sum that takes two integers and returns an integer?

A function sum(a, b int) int {}

B func sum(a int, b int) {}

C func sum(a int, b int) int {}

D def sum(a int, b int) int {}

Option C correctly uses Go syntax with func, parameter types, and return type.

Can a Go function return more than one value?

A No, Go does not support return values

B No, only one return value is allowed

C Yes, but only if parameters are also multiple

D Yes, by listing multiple return types in parentheses

Go supports multiple return values by listing them in parentheses after the function parameters.

What is the correct way to declare a function with no parameters and no return value?

A func hello() {}

B func hello {}

C func hello() -> void {}

D function hello() {}

In Go, empty parentheses indicate no parameters, and no return type means no return value.

Which of these is a valid function declaration in Go?

A function greet(name string) string { return "Hi " + name }

B func greet(name string) string { return "Hi " + name }

C func greet(name string) { return "Hi " + name }

D func greet(name) string { return "Hi " + name }

Option B correctly declares parameter type and return type with proper syntax.

Explain how to declare a function in Go that takes parameters and returns a value.

Think about the order: func, name, parameters, return type, then body.

Describe how Go functions can return multiple values and why this might be useful.

Remember Go often returns error as a second value.

Practice

1. What keyword is used to declare a function in Go?

easy

A. func

B. function

C. def

D. fun

Solution

1. Step 1: Recall Go function syntax

   In Go, functions are declared using the keyword func.

2. Step 2: Compare options

   Only func uses func, which is correct for Go.

3. Final Answer:

   func -> Option A

4. Quick Check:

   Function declaration keyword = func [OK]

Hint: Remember: Go uses 'func' to start a function [OK]

Common Mistakes:

• Using 'function' like JavaScript
• Using 'def' like Python
• Using 'fun' which is invalid

2. Which of the following is the correct syntax to declare a function named add that takes two integers and returns an integer?

easy

A. function add(a int, b int) int {}

B. func add(int a, int b) int {}

C. func add(a, b int) {}

D. func add(a int, b int) int {}

Solution

1. Step 1: Understand Go function parameter syntax

   In Go, parameters are declared as name type. So a int, b int is correct.

2. Step 2: Check return type and function keyword

   Function must start with func and specify return type int. func add(a int, b int) int {} matches this exactly.

3. Final Answer:

   func add(a int, b int) int {} -> Option D

4. Quick Check:

   Parameter syntax = name type [OK]

Hint: Parameters: name then type, return type after parentheses [OK]

Common Mistakes:

• Putting type before name in parameters
• Using 'function' keyword instead of 'func'
• Omitting return type when needed

3. What will be the output of this Go program?

package main
import "fmt"
func multiply(x int, y int) int {
    return x * y
}
func main() {
    fmt.Println(multiply(3, 4))
}

medium

A. 12

B. 7

C. 34

D. Error

Solution

1. Step 1: Understand function call and return

   The function multiply takes two integers and returns their product.

2. Step 2: Calculate multiply(3, 4)

   3 * 4 = 12, so the function returns 12, which is printed.

3. Final Answer:

   12 -> Option A

4. Quick Check:

   3 times 4 = 12 [OK]

Hint: Multiply parameters and print result [OK]

Common Mistakes:

• Adding instead of multiplying
• Concatenating numbers as strings
• Expecting syntax error due to function

4. Identify the error in this Go function declaration:

func greet(name string) string {
    return "Hello, " + name

medium

A. Incorrect function keyword

B. Wrong parameter type

C. Missing closing brace '}'

D. Missing return type

Solution

1. Step 1: Check function syntax

   The function starts with func, has parameter and return type correctly.

2. Step 2: Look for missing parts

   The function body is missing the closing brace } to end the function.

3. Final Answer:

   Missing closing brace '}' -> Option C

4. Quick Check:

   Every function must end with '}' [OK]

Hint: Count opening and closing braces carefully [OK]

Common Mistakes:

• Forgetting to close function body with '}'
• Confusing parameter types
• Omitting return type

5. How would you declare a Go function named filterEven that takes a slice of integers and returns a new slice containing only even numbers?

hard

A. func filterEven(nums int) int {
var evens int
for _, n := range nums {
if n%2 == 0 {
evens += n
}
}
return evens
}

B. func filterEven(nums []int) []int {
var evens []int
for _, n := range nums {
if n%2 == 0 {
evens = append(evens, n)
}
}
return evens
}

C. func filterEven(nums []int) {
for _, n := range nums {
if n%2 == 0 {
fmt.Println(n)
}
}
}

D. func filterEven(nums []int) []int {
for n := range nums {
if n%2 == 0 {
return nums
}
}
return nil
}

Solution

1. Step 1: Check parameter and return types

   The function must take a slice of integers []int and return a slice of integers []int. func filterEven(nums []int) []int { var evens []int for _, n := range nums { if n%2 == 0 { evens = append(evens, n) } } return evens } matches this.

2. Step 2: Verify logic to filter even numbers

   func filterEven(nums []int) []int { var evens []int for _, n := range nums { if n%2 == 0 { evens = append(evens, n) } } return evens } creates a new slice, loops over input, appends even numbers, and returns the new slice. This is correct.

3. Final Answer:

   func filterEven(nums []int) []int { var evens []int for _, n := range nums { if n%2 == 0 { evens = append(evens, n) } } return evens } -> Option B

4. Quick Check:

   Filter slice by appending evens [OK]

Hint: Use slice, loop, append evens, return new slice [OK]

Common Mistakes:

• Wrong parameter or return types
• Returning inside loop prematurely
• Printing instead of returning filtered slice