Returning errors in Go - Mini Project: Build & Apply

Returning errors

📖 Scenario: You are writing a simple program to check if a number is positive. If the number is not positive, you want to return an error message.

🎯 Goal: Build a Go program that defines a function to check if a number is positive and returns an error if it is not. Then call this function and handle the error properly.

📋 What You'll Learn

Create a function that returns an error when the input number is not positive

Use the built-in errors.New function to create the error

Call the function with a negative number to test error handling

Print the error message if an error is returned

💡 Why This Matters

🌍 Real World

Returning errors is important in real programs to handle unexpected situations like invalid input or failed operations.

💼 Career

Understanding how to return and handle errors is a key skill for Go developers working on reliable and maintainable software.

1

Create a function to check if a number is positive

Write a function called checkPositive that takes an int parameter named num and returns an error. The function should return nil for now.

Go

func checkPositive(num int) error {
    // Your code here
    return nil
}

Hint

Define the function with the correct name, parameter, and return type. Return nil to indicate no error.

2

Add error return for non-positive numbers

Modify the checkPositive function to return an error using errors.New with the message "number is not positive" if num is less than or equal to zero. Otherwise, return nil. Remember to import the errors package.

Go

package main

import "errors"

func checkPositive(num int) error {
    // Your code here
}

Hint

Use an if statement to check the number and return the error with errors.New.

3

Call the function and handle the error

In the main function, call checkPositive with the value -5 and store the result in a variable called err. Use an if statement to check if err is not nil.

Go

package main

import "errors"

func checkPositive(num int) error {
    if num <= 0 {
        return errors.New("number is not positive")
    }
    return nil
}

func main() {
    // Your code here
}

Hint

Call the function with -5 and check if the returned error is not nil.

4

Print the error message

Inside the if err != nil block, use fmt.Println(err) to print the error message. Remember to import the fmt package.

Go

package main

import (
    "errors"
    // Your code here
)

func checkPositive(num int) error {
    if num <= 0 {
        return errors.New("number is not positive")
    }
    return nil
}

func main() {
    err := checkPositive(-5)
    if err != nil {
        // Your code here
    }
}

Hint

Use fmt.Println(err) to show the error message on the screen.