PHP If Operators

An if statement is only as reliable as its condition. This lesson focuses on writing conditions: which operators and functions to use for numbers, strings, missing values, types, and lists, and how to combine them correctly. Most real bugs in if statements are not in the if itself but in a condition that does not mean exactly what the author intended.

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Operators Used in Conditions

Comparison Operators

Operator	Meaning	Example	true When
===	Identical	$status === 'paid'	Same value and type
!==	Not identical	$code !== ''	Different value or type
==	Equal (with type juggling)	$qty == '5'	Equal after conversion
!= / <>	Not equal (with type juggling)	$a != $b	Not equal after conversion
>	Greater than	$stock > 0	Left is larger
<	Less than	$age < 18	Left is smaller
>=	Greater than or equal	$score >= 40	Left is larger or equal
<=	Less than or equal	$items <= 10	Left is smaller or equal

Logical Operators

Operator	Meaning	Example
&&	Both must be true	$age >= 18 && $hasId
||	At least one must be true	$isAdmin || $isOwner
!	Reverses a condition	!$isBlocked

Details are in Comparison Operators and Logical Operators. This lesson applies them to common real-world checks.

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Checking Numbers and Ranges

Basic Comparisons

<?php
$stock = 4;

if ($stock === 0) {
    echo "Out of stock\n";
} elseif ($stock < 5) {
    echo "Only $stock left\n";
} else {
    echo "In stock\n";
}

Output

Only 4 left

Ranges

PHP has no "between" operator. Combine two comparisons with &&, and decide for each boundary whether it is inclusive (<=, >=) or exclusive (<, >):

<?php
function isBetween(int|float $value, int|float $min, int|float $max): bool
{
    return $value >= $min && $value <= $max;
}

$hour = 18;

if (isBetween($hour, 9, 17)) {
    echo "Support is online\n";
} else {
    echo "Support is offline (hours: 9–17)\n";
}

var_dump(isBetween(17, 9, 17));
var_dump(isBetween(17.5, 9, 17));

Output

Support is offline (hours: 9–17)
bool(true)
bool(false)

Testing the boundary values (here 17) is the quickest way to catch off-by-one mistakes. A helper function with a clear name also documents the rule.

Numbers From Input

Input from forms and URLs is always a string. Convert and validate before comparing:

<?php
$input = '25abc';

$qty = filter_var($input, FILTER_VALIDATE_INT, ['options' => ['min_range' => 1, 'max_range' => 99]]);

if ($qty === false) {
    echo "Quantity must be a whole number from 1 to 99\n";
} else {
    echo "Adding $qty items\n";
}

Output

Quantity must be a whole number from 1 to 99

filter_var() returns an int or false. Comparing with === false matters because a valid result could be falsy in other situations (for example, 0 when zero is allowed).

---

Checking Strings

Exact Match

<?php
$status = 'shipped';

if ($status === 'shipped' || $status === 'delivered') {
    echo "Tracking available\n";
}

Output

Tracking available

Case-Insensitive Match

<?php
$role = 'Admin';

if (strcasecmp($role, 'admin') === 0) {
    echo "Admin access\n";
}

if (mb_strtolower($role) === 'admin') {
    echo "Admin access (normalized)\n";
}

Output

Admin access
Admin access (normalized)

strcasecmp() returns 0 when the strings are equal ignoring case. Normalizing with mb_strtolower() also works for non-English text. Even better, normalize values once when you receive them, and compare normalized values everywhere else.

Contains, Starts With, Ends With (PHP 8.0+)

<?php
$url = 'https://gocourse.in/php/if-operators';
$file = 'report.PDF';

if (str_starts_with($url, 'https://')) {
    echo "Secure URL\n";
}

if (str_contains($url, '/php/')) {
    echo "PHP section\n";
}

if (str_ends_with(strtolower($file), '.pdf')) {
    echo "PDF document\n";
}

Output

Secure URL
PHP section
PDF document

These functions return real booleans, so they can be used directly as conditions — unlike strpos(), which returns 0 for a match at the start (see Search in Strings).

Empty Strings and Whitespace

<?php
$comment = "   ";

if ($comment === '') {
    echo "Exactly empty\n";
}

if (trim($comment) === '') {
    echo "Empty or only whitespace\n";
}

Output

Empty or only whitespace

A field containing only spaces is not ''. Trim user input before checking whether it is empty.

---

Checking for Missing or Empty Values

PHP offers several tools that look similar but answer different questions:

Check	Question It Answers
isset($x)	Does $x exist and is it not null?
$x === null	Is the value exactly null? (Warning if $x does not exist.)
empty($x)	Is $x missing or falsy ('', '0', 0, 0.0, null, false, [])?
$x === ''	Is the value exactly an empty string?
array_key_exists('k', $arr)	Does the key exist, even if its value is null?
count($arr) > 0 / $arr !== []	Does the array contain any elements?

How They Behave

Value	isset()	empty()	=== null	=== ''
(undefined)	false	true	Warning, then true	Warning, then false
null	false	true	true	false
''	true	true	false	true
'0'	true	true	false	false
0	true	true	false	false
' ' (spaces)	true	false	false	false
[]	true	true	false	false
'PHP'	true	false	false	false

The empty() Trap

empty() treats '0' and 0 as empty. That is wrong when zero is a meaningful answer:

<?php
$form = ['children' => '0', 'nickname' => ''];

if (empty($form['children'])) {
    echo "empty(): children is missing\n";
}

if (!isset($form['children']) || trim($form['children']) === '') {
    echo "explicit: children is missing\n";
} else {
    echo "explicit: children = {$form['children']}\n";
}

Output

empty(): children is missing
explicit: children = 0

The user answered "0 children", but empty() reports the field as missing. The explicit check treats only a missing key or a blank value as missing. Prefer explicit checks for user input; use empty() only when every falsy value really should count as empty.

Optional Values With ??

<?php
$query = [];

if (($query['debug'] ?? '') === '1') {
    echo "Debug mode\n";
} else {
    echo "Normal mode\n";
}

Output

Normal mode

?? supplies a default when the key is missing, which avoids "Undefined array key" warnings without a separate isset() call.

---

Checking Types

<?php
$values = [42, '42', 4.2, null, ['a'], new DateTime()];

foreach ($values as $value) {
    $type = get_debug_type($value);

    if (is_int($value)) {
        echo "$type: integer\n";
    } elseif (is_numeric($value)) {
        echo "$type: numeric (int-like or float-like)\n";
    } elseif (is_array($value)) {
        echo "$type: array with " . count($value) . " element(s)\n";
    } elseif ($value instanceof DateTimeInterface) {
        echo "$type: a date object\n";
    } elseif ($value === null) {
        echo "$type: no value\n";
    }
}

Output

int: integer
string: numeric (int-like or float-like)
float: numeric (int-like or float-like)
null: no value
array: array with 1 element(s)
DateTime: a date object

Function / Operator	true For
is_int(), is_float(), is_string(), is_bool(), is_array()	That exact type
is_numeric()	Numbers and numeric strings ('42', '4.2', '1e3')
is_null()	null (same as === null)
instanceof	Objects of a class, subclass, or interface

Note that is_numeric() accepts strings, so '42' passes it but fails is_int(). With type declarations on function parameters, many of these checks become unnecessary, because PHP enforces the types (see Type Declarations in Functions).

---

Checking Membership in a List

in_array() With Strict Mode

<?php
$allowedPlans = ['free', 'pro', 'business'];
$plan = 'Pro';

if (in_array(strtolower($plan), $allowedPlans, true)) {
    echo "Valid plan\n";
}

Output

Valid plan

Always pass true as the third argument. Without it, in_array() compares loosely (==), which can match unexpected values.

Many Equality Checks → in_array() or match

Instead of:

if ($day === 'Sat' || $day === 'Sun') { ... }

write:

if (in_array($day, ['Sat', 'Sun'], true)) { ... }

The list is easier to extend and read. When each value should produce a different result, use match (see PHP Match).

Keys vs Values

<?php
$prices = ['pen' => 15, 'book' => null];

var_dump(isset($prices['book']));
var_dump(array_key_exists('book', $prices));
var_dump(in_array(15, $prices, true));

Output

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

• isset() is false because the value is null.
• array_key_exists() is true because the key exists.
• in_array() searches the values, not the keys.

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Combining and Negating Conditions

Group With Parentheses

<?php
$isAdmin = false;
$isAuthor = true;
$isPublished = false;

if ($isAdmin || ($isAuthor && !$isPublished)) {
    echo "You can edit this draft\n";
}

Output

You can edit this draft

&& binds more tightly than ||, so the parentheses do not change the result here — but they make the intended grouping obvious.

Negate the Whole Condition

<?php
$age = 16;
$hasConsent = false;

if (!($age >= 18 || $hasConsent)) {
    echo "Registration not allowed\n";
}

if ($age < 18 && !$hasConsent) {
    echo "Registration not allowed (simplified)\n";
}

Output

Registration not allowed
Registration not allowed (simplified)

The second form applies De Morgan's law: "not (A or B)" equals "not A and not B". Positive, simplified conditions are usually easier to read than negated groups.

Name Complex Conditions

<?php
$order = ['total' => 1800, 'country' => 'IN', 'weight_kg' => 3];

$isDomestic = $order['country'] === 'IN';
$isLight = $order['weight_kg'] <= 5;
$qualifiesByTotal = $order['total'] >= 999;

if ($isDomestic && $isLight && $qualifiesByTotal) {
    echo "Free shipping\n";
}

Output

Free shipping

Each part of the rule has a name, so the if reads like the business rule itself.

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Practical Example: Validating a Signup Form

<?php
function validateSignup(array $input): array
{
    $errors = [];

    $name = trim($input['name'] ?? '');
    $email = trim($input['email'] ?? '');
    $age = filter_var($input['age'] ?? '', FILTER_VALIDATE_INT);
    $plan = $input['plan'] ?? '';
    $terms = $input['terms'] ?? null;

    if ($name === '') {
        $errors['name'] = 'Name is required.';
    } elseif (mb_strlen($name) > 50) {
        $errors['name'] = 'Name must be at most 50 characters.';
    }

    if (filter_var($email, FILTER_VALIDATE_EMAIL) === false) {
        $errors['email'] = 'Enter a valid email address.';
    }

    if ($age === false || $age < 13 || $age > 120) {
        $errors['age'] = 'Age must be between 13 and 120.';
    }

    if (!in_array($plan, ['free', 'pro'], true)) {
        $errors['plan'] = 'Choose the free or pro plan.';
    }

    if ($terms !== 'yes') {
        $errors['terms'] = 'You must accept the terms.';
    }

    return $errors;
}

print_r(validateSignup([
    'name' => '   ',
    'email' => 'priya@',
    'age' => '0',
    'plan' => 'gold',
]));

print_r(validateSignup([
    'name' => 'Priya',
    'email' => 'priya@example.com',
    'age' => '24',
    'plan' => 'pro',
    'terms' => 'yes',
]));

Output

Array
(
    [name] => Name is required.
    [email] => Enter a valid email address.
    [age] => Age must be between 13 and 120.
    [plan] => Choose the free or pro plan.
    [terms] => You must accept the terms.
)
Array
(
)

How Each Condition Works

Field	Condition	Why It Is Written This Way
Name	trim(...) === '', then mb_strlen() > 50	Whitespace-only names are rejected; length counts characters, not bytes
Email	filter_var(..., FILTER_VALIDATE_EMAIL) === false	Uses PHP's validator and a strict check against false
Age	$age === false || $age < 13 || $age > 120	false means "not an integer"; short-circuiting ensures the range checks run only on real integers
Plan	!in_array($plan, [...], true)	Allow-list with strict comparison
Terms	$terms !== 'yes'	Only the exact expected value counts as acceptance; a missing checkbox gives null

Separate if statements are used because several fields can be invalid at once, and the user should see all errors together. The elseif inside the name check is used because "required" and "too long" cannot both apply.

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Common Mistakes

Mistake	Effect	Better Condition
if ($x = 5)	Assignment; always true	if ($x === 5)
if (strpos($s, 'a'))	Match at position 0 treated as false	if (str_contains($s, 'a'))
if (empty($qty)) for numeric input	0 treated as missing	if (trim($qty) === '') then validate
if ($input == 0)	Loose comparison with strings	Validate, then === 0
if (in_array($v, $list))	Loose matching	in_array($v, $list, true)
if (!$a > 5)	(!$a) > 5	if (!($a > 5)) or if ($a <= 5)
`if ($a		$b && $c)`	Grouping unclear	Add parentheses

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Best Practices

• Use strict comparisons (===, !==) and strict in_array().
• Trim and validate input before comparing it; compare typed values, not raw strings.
• Choose the right existence check: isset(), ??, array_key_exists(), or an explicit === ''.
• Avoid empty() for values where 0 or '0' are valid.
• Prefer boolean-returning functions (str_contains(), filter_var() with strict checks) over position-returning ones in conditions.
• Name complex conditions and use parentheses when mixing && and ||.

Official reference: https://www.php.net/manual/en/language.operators.comparison.php