Check Odd Number in PHP

What You’ll Learn

An integer is odd when it is not divisible by 2 — in PHP, when $n % 2 != 0. This tutorial covers the modulo test, why zero is not odd, range listing, a live preview, worked PHP examples, edge cases, and complexity.

📝 Problem & Approach

Given an integer, decide whether it is odd using remainder modulo 2. Optionally list all odds in a closed range.

// 15 % 2 = 1  -> odd
// 14 % 2 = 0  -> not odd
// 0  % 2 = 0  -> not odd (even)

Inputs & Outputs

Minimal workflow

function isOdd(n):
    return (n mod 2) != 0

function printOddsInRange(start, end):
    for i from start to end:
        if isOdd(i):
            output i

Method comparison

🔮 Live Preview

Uses JavaScript safe integers. The rule matches the PHP idea: odd when n % 2 !== 0.

Press “Is it odd?” to see the verdict.

Examples Gallery

Three complete PHP programs — single odd check for 15, print odds in 1..10, and a step-by-two range list. Click View Output to reveal sample console results.

<?php
function isOdd(int $number): bool
{
    return $number % 2 != 0;
}

$number = 15;

if (isOdd($number)) {
    echo $number . " is an odd number.\n";
} else {
    echo $number . " is not an odd number.\n";
}
?>

15 is an odd number.

<?php
function printOddNumbersFrom1To10(): void
{
    echo "Odd numbers in the range 1 to 10:\n";
    for ($i = 1; $i <= 10; $i++) {
        if ($i % 2 != 0) {
            echo $i . " ";
        }
    }
    echo "\n";
}

printOddNumbersFrom1To10();
?>

Odd numbers in the range 1 to 10:
1 3 5 7 9

<?php
function printOddsStepByTwo(int $start, int $end): void
{
    if ($start % 2 == 0) {
        $start++;
    }

    echo "Odd numbers from $start toward $end (step 2):\n";
    for ($i = $start; $i <= $end; $i += 2) {
        echo $i . " ";
    }
    echo "\n";
}

printOddsStepByTwo(1, 10);
?>

Odd numbers from 1 toward 10 (step 2):
1 3 5 7 9

🔎 Worked Walkthrough — Sample Values

Apply $n % 2 != 0 to a few integers.

For nonnegative beginners, “remainder 1” is the usual mental picture of odd.

⚖️ Facts Worth Knowing

Handy follow-ups interviewers sometimes ask.

🎯 Practice Problems

Try these variations to lock in the pattern.

Notes

⏱️ Time and Space Complexity

No heap allocation is required for these snippets.

💡 Best Practices