Basic Conditional Statements in PHP: if, else, elseif

Conditional statements are the foundation of programming in PHP. They allow your script to make decisions: execute one part of code or another depending on conditions. Without conditionals, it would be difficult to write user logins, shopping cart logic, form validation, or personalized content.

• In this lesson, you’ll learn the basics: if, else, and elseif.
• You’ll see simple and practical PHP code examples.
• You’ll learn best practices and avoid common mistakes.

The previous lesson covered arrays and their functions — now we’ll show how to combine arrays with conditionals (e.g., checking if an array is not empty before doing something).

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Basics of Conditional Statements in PHP

What is a condition?

A condition is an expression that evaluates to a boolean: true or false. Based on this result, PHP decides which block of code to execute.

• if (condition) — executes the block if the condition is true.
• else — executes the alternative block if the condition is false.
• elseif (another_condition) — adds more tests if the previous ones were not met.

if syntax

<?php
$isLoggedIn = true;

if ($isLoggedIn) {
    echo "Welcome back!";
}

if...else syntax

<?php
$hour = (int) date('H'); // e.g. 0..23

if ($hour < 12) {
    echo "Good morning!";
} else {
    echo "Good evening!";
}

if...elseif...else syntax

PHP executes only the first block where the condition is true; the rest are skipped.

<?php
$points = 78;

if ($points >= 90) {
    echo "Grade: A";
} elseif ($points >= 75) {
    echo "Grade: B";
} elseif ($points >= 60) {
    echo "Grade: C";
} else {
    echo "Grade: D";
}

Important: truthy and falsy in PHP

In PHP, some values are treated as false, even if they’re not literally false:

• False: false, 0, 0.0, "" (empty string), "0" (string zero!), [] (empty array), null
• True: everything else (e.g., "abc", 1, -5, [1,2], object)

⚠️ Note: "0" is treated as false — a common source of confusion.

Comparison and logical operators

• Comparisons: ==, === (identical: type and value), !=, !==, <, >, <=, >=
• Logical: && (and), || (or), ! (not)
• There are also and, or with lower precedence — usually stick to && and ||.

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PHP Code Examples (with comments)

1) Simple condition: access only for adults

<?php
$age = 19;

if ($age >= 18) {
    echo "You have access to this section.";
}

2) if...else: greeting depending on the time

<?php
$hour = (int) date('H');

if ($hour < 12) {
    echo "Good morning!";
} else {
    echo "Good afternoon!";
}

3) if...elseif...else: discount thresholds

<?php
$cartValue = 260;

if ($cartValue >= 500) {
    echo "15% discount";
} elseif ($cartValue >= 200) {
    echo "7% discount";
} elseif ($cartValue >= 100) {
    echo "3% discount";
} else {
    echo "No discount";
}

4) Nested conditions and combining operators

<?php
$country = "PL";
$age = 20;
$hasConsent = true;

if ($country === "PL" && $age >= 18) {
    if ($hasConsent) {
        echo "You can participate in the contest.";
    } else {
        echo "We need your consent.";
    }
} else {
    echo "Criteria not met.";
}

5) Working with arrays (linking to previous lesson)

<?php
$products = ["monitor", "mouse", "keyboard"];

// empty($products) returns true for an empty array
if (!empty($products)) {
    echo "We have " . count($products) . " products in stock.";
} else {
    echo "No products available.";
}

// Checking for a value in an array
if (in_array("mouse", $products, true)) { // true => strict comparison
    echo "Mouse is available.";
}

6) Safe key checking in associative arrays

<?php
$user = [
    "login" => "ola",
    // "age" => 17 // commented: key may not exist
];

// isset checks if the key exists and is not null
if (isset($user["age"]) && $user["age"] >= 18) {
    echo "User is an adult.";
} else {
    echo "Age missing or user underage.";
}

7) Loose vs strict comparisons (== vs ===)

<?php
$num = 0;
$text = "0";

if ($num == $text) {
    echo "== considers values equal (type conversion).";
}

if ($num === $text) {
    echo "This won’t print, because types differ (int vs string).";
}

8) Beware operator precedence: && vs and

<?php
$result = false;
$a = true;
$b = false;

// && has higher precedence than =
$result = $a && $b; // ($a && $b) → false, then assignment
var_dump($result); // bool(false)

// and has lower precedence than =
$result = $a and $b; // ($result = $a) → true assigned, then true and $b → false
var_dump($result); // bool(true) — surprise!

// Use && and || and add parentheses for clarity

9) Using if in templates (alternative syntax)

Alternative syntax with endif; helps mixing PHP with HTML.

<?php
$isLoggedIn = true;
$login = "ola";
?>

<div class="welcome">
    <?php if ($isLoggedIn): ?>
        <p>Welcome, <?= htmlspecialchars($login) ?>!</p>
    <?php elseif (!$isLoggedIn): ?>
        <p>Welcome, Guest!</p>
    <?php else: ?>
        <p>Unknown login state.</p>
    <?php endif; ?>
</div>

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Best Practices and Common Mistakes

Best Practices

• Always use curly braces { }, even for single statements — improves readability and prevents errors.
• Prefer strict comparisons (===, !==) instead of == and !=, especially for form/API data.
• Simplify conditions — use well-named intermediate variables:

  $isAdult = isset($user["age"]) && $user["age"] >= 18;
  if ($isAdult) { ... }

• Avoid deep nesting — use guard clauses (early returns):

  if (!$isLoggedIn) {
      echo "Please log in";
      return;
  }
  // further code for logged-in users...

• Add parentheses in complex conditions for clarity.
• Stick to one convention: use elseif (recommended) instead of else if.
• Use isset() to check if keys exist; use empty() for “is empty” (be careful with "0").
• Escape output in HTML (e.g., htmlspecialchars) and validate inputs.

Common Mistakes

• Using = instead of == or === in conditions:

  if ($a = 5) { ... } // ERROR: assignment instead of comparison

• Missing braces leading to “dangling else” problems.
• Confusing precedence of and/or with &&/|| — stick to && and ||.
• Misunderstanding truthy/falsy: e.g., "0" is false, so if ("0") { ... } won’t run.
• Checking values without confirming key existence:

  if ($user["age"] > 18) { ... } // Notice if 'age' doesn’t exist

Instead:

  if (isset($user["age"]) && $user["age"] > 18) { ... }

• Comparing to null loosely (==) instead of strictly (=== or is_null()).

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Summary

• Conditional statements if, else, elseif control program flow in PHP.
• Conditions rely on true/false; remember truthy/falsy rules.
• Use strict comparisons (===, !==), braces, and parentheses for clarity and safety.
• Avoid pitfalls: = instead of ==, precedence issues with and, missing isset().
• Alternative syntax if: ... elseif: ... else: ... endif; is handy in templates.

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Mini Quiz — Test Yourself!

• What will this print?

<?php
$value = "0";
if ($value) {
    echo "A";
} else {
    echo "B";
}

➡️ B

• Which syntax is recommended in PHP?

➡️ elseif

• What’s the output?

var_dump(0 == "0");
var_dump(0 === "0");

➡️ true, false

• Safer way to check user’s age in $u:

➡️ if (isset($u["age"]) && $u["age"] >= 18) { ... }

• Difference between && and and?

➡️ Both are logical AND, but with different precedence.

• What prints?

$result = false;
$a = true;
$b = false;

$result = $a and $b;
var_dump($result);

➡️ bool(true)

• In an if ... elseif ... else chain, which block executes?

➡️ Only the first block where the condition is true.

• True or false: empty([]) returns true.

➡️ True

• What’s the result?

if ("10" > 2) {
    echo "X";
} else {
    echo "Y";
}

➡️ X

• Which comparison is safer for form data (string vs int)?

➡️ ===

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Now you know the basic conditional statements in PHP: if, else, and elseif. Practice creating conditions based on form data and arrays, and you’ll quickly feel confident programming in PHP.