Check Natural Number in PHP

What You’ll Learn

Under this tutorial’s definition, a natural number is a positive integer: n > 0. This page covers the one-comparison check, printing a counting range, CLI validation, a live preview, worked PHP examples, edge cases, and complexity.

📝 Problem & Approach

Given an integer, decide whether it is natural under the rule num > 0, and optionally print counting numbers in a range.

// 42  -> natural (42 > 0)
// 0   -> not natural under n > 0
// -3  -> not natural

Inputs & Outputs

Minimal workflow

function isNatural(num):   // integer
    if num > 0:
        return true
    return false

Method comparison

🔮 Live Preview

Uses the same rule as the code: natural means integer > 0.

Press “Check”.

Examples Gallery

Three complete PHP programs — single yes/no check, print 1 through 10, and CLI input with validation. Click View Output to reveal sample console results.

<?php
function isNatural(int $num): bool
{
    return $num > 0;
}

$number = 42;

if (isNatural($number)) {
    echo $number . " is a natural number.\n";
} else {
    echo $number . " is not a natural number.\n";
}
?>

42 is a natural number.

<?php
function printNaturalsInRange(int $start, int $end): void
{
    echo "Natural numbers in the range $start to $end:\n";
    for ($i = $start; $i <= $end; $i++) {
        if ($i > 0) {
            echo $i . " ";
        }
    }
    echo "\n";
}

printNaturalsInRange(1, 10);
?>

Natural numbers in the range 1 to 10:
1 2 3 4 5 6 7 8 9 10 

<?php
function isNatural(int $num): bool
{
    return $num > 0;
}

echo "Enter an integer: ";
$raw = trim(fgets(STDIN));

if (!is_numeric($raw) || strpos($raw, ".") !== false) {
    echo "Please enter a whole number.\n";
    exit(1);
}

$number = (int)$raw;

if (isNatural($number)) {
    echo $number . " is a natural number.\n";
} else {
    echo $number . " is not a natural number.\n";
}
?>

Enter an integer: 0
0 is not a natural number.

🔎 Worked Walkthrough — Sample Values

Apply $num > 0 to a few integers.

If your course includes zero, change the test to >= and update the wording together.

⚖️ Facts Worth Knowing

Handy follow-ups interviewers sometimes ask.

🎯 Practice Problems

Try these variations to lock in the pattern.

Notes

⏱️ Time and Space Complexity

The interesting part is the definition, not the asymptotic cost.

💡 Best Practices