Odd, even numbers

Some numbers are odd. Others are even. We can use modulo division to tell whether a number is divisible by two. This tells us the parity of a number.

An odd issue

To tell if a number is even, we see if it is evenly divisible by 2. But to tell if it is odd, we must allow a remainder of either 1 or -1. A negative number may be odd.

Example program

This program introduces the Even and Odd funcs. We test Even() and Odd() in the main method. Both methods return a bool.

package main

import "fmt"

func Even(number int) bool {
    return number%2 == 0
}

func Odd(number int) bool {
    // Odd should return not even.
    // ... We cannot check for 1 remainder.
    // ... That fails for negative numbers.
    return !Even(number)
}

func main() {
    for i := -4; i <= 4; i++ {
        // Test the even func.
        fmt.Printf("Number: %v, Even: %v", i, Even(i))
        fmt.Println()
    }

    // Test the odd method.
    if Odd(1) {
        fmt.Println("ok")
    }
}
Number: -4, Even: true
Number: -3, Even: false
Number: -2, Even: true
Number: -1, Even: false
Number: 0, Even: true
Number: 1, Even: false
Number: 2, Even: true
Number: 3, Even: false
Number: 4, Even: true
ok

Simple methods

In the math package, I found no methods that reveal the parity of numbers. So a simple method that tells us this can be useful in quick Go programs.

In general, using built-in methods from the "math" package is the best choice. So it is worthwhile to check that no existing math methods are available.