Chapter 3 - Functions

Exercise 3: Error Handling

Update your perimeter function from the previous exercise to return an error if either the length or width are negative.

• If the given length is negative, return a perimeter of 0 and an error with the message “a length of [length] is invalid”.
• If the given width is negative, return a perimeter of 0 and an error with the message “a width of [width] is invalid”.
• Otherwise, return the calculated perimeter, and an error value of nil.

In your main function, test returning an error by calling perimeter with a negative value. If the returned error value is not nil, print the error message and exit the program. Otherwise, print the returned perimeter.

Solution

package main

import (
    "fmt"
    "log"
)

func perimeter(length float64, width float64) (float64, error) {
    if length < 0 {
        return 0, fmt.Errorf("a length of %0.2f is invalid", length)
    }
    if width < 0 {
        return 0, fmt.Errorf("a width of %0.2f is invalid", width)
    }
    return length*2 + width*2, nil
}

func main() {
    p, err := perimeter(8.2, -10)
    if err != nil {
        log.Fatal(err)
    }
    fmt.Println(p)
}

Output:

2019/05/25 15:06:35 a width of -10.00 is invalid
exit status 1