if, else and elseif

Decisions are at the heart of every program: show the login form or the dashboard, charge shipping or not, accept the input or reject it. PHP makes decisions with if, else and elseif, and offers an alternative syntax that reads well inside HTML templates.

if

The condition goes in parentheses. If it's true (or truthy — lesson 9), the block runs:

PHP

<?php

$temperature = 31;

if ($temperature > 30) {
    echo "It's hot today.\n";
    echo "Drink plenty of water.\n";
}
echo "Done.\n";

Output

It's hot today.
Drink plenty of water.
Done.

else and elseif

else runs when the condition is false. elseif tests further conditions in order; the first true one wins and the rest are skipped:

PHP

<?php

foreach ([95, 82, 67, 45] as $score) {
    if ($score >= 90) {
        $grade = "A";
    } elseif ($score >= 80) {
        $grade = "B";
    } elseif ($score >= 65) {
        $grade = "C";
    } else {
        $grade = "F";
    }
    echo "$score: $grade\n";
}

Output

95: A
82: B
67: C
45: F

Order matters: 95 also satisfies $score >= 80, so the highest threshold must be checked first. (PHP also accepts else if with a space; elseif is the usual style.)

Combining conditions

PHP

<?php

$age = 34;
$hasTicket = true;
$isVip = false;

if ($age >= 18 && ($hasTicket || $isVip)) {
    echo "Welcome in.\n";
}

if (!($age >= 13 && $age <= 19)) {
    echo "Not a teenager.\n";
}

$role = "editor";
if (in_array($role, ["admin", "editor"], true)) {
    echo "Can publish articles.\n";
}

Output

Welcome in.
Not a teenager.
Can publish articles.

in_array with true (strict mode) is a neat way to test "is it one of these values?".

Guard clauses

Deeply nested ifs are hard to read. Handle the problem cases first and stop early — with return in a function, or exit in a script:

PHP

<?php

function checkout(array $cart, ?string $user): string
{
    if ($user === null) {
        return "Please log in first.";
    }
    if ($cart === []) {
        return "Your cart is empty.";
    }
    return "Checking out " . count($cart) . " item(s) for $user.";
}

echo checkout([], null), "\n";
echo checkout([], "sam"), "\n";
echo checkout(["book", "pen"], "sam"), "\n";

Output

Please log in first.
Your cart is empty.
Checking out 2 item(s) for sam.

Truthiness traps

Because if accepts any value, it's tempting to write if ($value). That treats 0, "", "0" and [] as false, which is often not what you mean:

PHP

<?php

$quantity = "0";   // e.g. from a form field

if ($quantity) {
    echo "truthy check: has a quantity\n";
} else {
    echo "truthy check: no quantity (wrong!)\n";
}

if ($quantity !== "") {
    echo "explicit check: quantity entered\n";
}

Output

truthy check: no quantity (wrong!)
explicit check: quantity entered

Compare explicitly — === null, === '', === [], > 0 — whenever 0 or "0" could be a legitimate value.

Comparing strings

=== compares strings exactly, case included. For a case-insensitive comparison, use strcasecmp, which returns 0 when the strings match:

PHP

<?php

$answer = "YES";

var_dump($answer === "yes");
var_dump(strcasecmp($answer, "yes") === 0);
var_dump(strtolower($answer) === "yes");

Output

bool(false)
bool(true)
bool(true)

Alternative syntax for templates

In files that mix PHP and HTML, braces get lost among the tags. PHP's alternative syntax replaces { with a colon and } with endif;:

PHP status.php

<?php $stock = (int) ($_GET['stock'] ?? 0); ?>
<?php if ($stock > 10): ?>
<p class="ok">In stock</p>
<?php elseif ($stock > 0): ?>
<p class="warn">Only <?= $stock ?> left!</p>
<?php else: ?>
<p class="none">Sold out</p>
<?php endif; ?>

HTTP

GET /status.php?stock=25
GET /status.php?stock=3
GET /status.php

Responses

> GET /status.php?stock=25
<p class="ok">In stock</p>
> GET /status.php?stock=3
<p class="warn">Only 3 left!</p>
> GET /status.php
<p class="none">Sold out</p>

The same style exists for loops: foreach (...): … endforeach;, for/endfor and while/endwhile.

Try it yourself

Calculate a shipping cost: free over 50, 4.99 for orders of 20 or more, 7.99 otherwise; express shipping adds 10.

Output

Shipping: 14.99
Total: 49.99

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