Function declaration in Go - Mini Project: Build & Apply

Function declaration

📖 Scenario: You are creating a simple calculator program in Go that can add two numbers.

🎯 Goal: Build a Go program that declares a function to add two integers and then uses it to show the result.

📋 What You'll Learn

Declare a function named add that takes two int parameters and returns their sum as int.

Call the add function with two numbers.

Print the result of the addition.

💡 Why This Matters

🌍 Real World

Functions help organize code into reusable blocks, just like recipes in cooking. You can use them to perform tasks many times without rewriting code.

💼 Career

Knowing how to declare and use functions is essential for any software developer. It helps write clean, maintainable, and reusable code.

1

Create two integer variables

Create two integer variables called a and b with values 5 and 7 respectively.

Go

package main

import "fmt"

func main() {
    // Create two integer variables a and b with values 5 and 7
    // Your code here
}

Hint

Use := to declare and assign variables in Go.

2

Declare the add function

Declare a function named add that takes two int parameters named x and y and returns their sum as int.

Go

package main

import "fmt"

func add(x int, y int) int {
    // Your code here
}

func main() {
    a := 5
    b := 7
}

Hint

Use func add(x int, y int) int to declare the function and return x + y to return the sum.

3

Call the add function

Inside main, call the add function with a and b and store the result in a variable called result.

Go

package main

import "fmt"

func add(x int, y int) int {
    return x + y
}

func main() {
    a := 5
    b := 7
    // Call add with a and b, store in result
    // Your code here
}

Hint

Use result := add(a, b) to call the function and save the sum.

4

Print the result

Print the value of the variable result using fmt.Println.

Go

package main

import "fmt"

func add(x int, y int) int {
    return x + y
}

func main() {
    a := 5
    b := 7
    result := add(a, b)
    // Print the result
    // Your code here
}

Hint

Use fmt.Println(result) to print the sum.

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