Conditionals: if, else, and switch

So far your scripts have run straight through, top to bottom, doing the same thing every time. Real programs need to make decisions: show a discount if the cart is big enough, greet a user if they are logged in, print “pass” or “fail” depending on a score. That is what conditionals do. They let your code pick a path.

The if Statement

An if statement runs a block of code only when a condition is true. The shape is always the same: the keyword if, a condition in parentheses, then a block in curly braces.

<?php
$score = 75;
if ($score >= 50) {
    echo "You passed";
}

You passed

Read it out loud: “if score is greater than or equal to 50, print You passed.” The condition $score >= 50 is one of the comparisons from the last lesson, and it produces a boolean, either true or false. When it is true, the code in the braces runs. When it is false, PHP skips the braces entirely and moves on. Change $score to 30 and run it again: nothing prints, because the condition is false.

else and elseif

Often you want a fallback: do one thing when the condition is true, and something else when it is false. That is what else is for. And when there are more than two paths, elseif lets you test another condition.

<?php
$score = 72;
if ($score >= 90) {
    echo "Grade A";
} elseif ($score >= 70) {
    echo "Grade B";
} else {
    echo "Keep practicing";
}

Grade B

PHP checks the conditions from top to bottom and takes the first one that is true, then skips the rest. Here 72 >= 90 is false, so it moves on. 72 >= 70 is true, so it prints “Grade B” and stops. The final else has no condition; it is the catch-all that runs when every test above it failed. You can have as many elseif branches as you like, but only one runs.

Truthy and Falsy

A condition does not have to be a comparison. You can put a single value in the parentheses, and PHP decides whether it counts as true or false. Most values are “truthy,” but a short, fixed list of values are “falsy,” meaning PHP treats them as false. Learn this list, because it catches everyone eventually. These values are falsy:

• The integer 0 and the float 0.0
• The empty string "" and the string "0"
• null
• false itself
• The empty array []

Everything else is truthy: any other number, any other text, a non-empty array. The one that surprises people is the string "0". It looks harmless, but PHP counts it as false. Make a prediction before you run it.

<?php
if ("0") {
    echo "yes";
} else {
    echo "no";
}

Choosing With switch

When you are comparing one variable against a list of specific values, a long if/elseif chain gets repetitive. The switch statement is built for exactly this. You give it a value once, then list the cases to match.

<?php
$day = 3;
switch ($day) {
    case 1:
        echo "Monday";
        break;
    case 2:
        echo "Tuesday";
        break;
    case 3:
        echo "Wednesday";
        break;
    default:
        echo "Another day";
}

Wednesday

PHP compares $day against each case in turn. When it finds a match it runs that block, and break tells it to stop and leave the switch. The default case is the catch-all, like else: it runs when nothing else matched. A switch reads much more cleanly than five elseif lines that all compare the same variable.

A Look at match

PHP 8 added match, a tidier cousin of switch. It returns a value you can store, it needs no break, and it uses strict comparison (===), so no surprise type juggling. Notice each arm uses => and the whole thing ends with a semicolon, because it is an expression.

<?php
$day = 3;
$name = match ($day) {
    1 => "Monday",
    2 => "Tuesday",
    3 => "Wednesday",
    default => "Another day",
};
echo $name;

Wednesday

You can also list several values on one arm, separated by commas, such as 6, 7 => "Weekend". Reach for match when each branch simply produces a value; reach for switch or an if chain when a branch needs to run several statements.

Providing a Fallback: ?? and ?:

A very common decision is simply “use this value if I have one, otherwise fall back to something else.” The null coalescing operator ?? does exactly that: $a ?? $b gives you $a when it is set and not null, and $b otherwise. It also quietly handles an undefined variable or missing array key without a warning, which makes it perfect for reading optional input.

<?php
$name = $_GET["name"] ?? "guest";
echo $name;

guest

The $_GET array holds values from the page’s URL, which you will meet properly later; here it is empty, so $name falls back to "guest" with no undefined-key warning. There is also the shorter ternary ?:, where $a ?: $b gives $a when it is truthy and $b otherwise. The difference matters: ?? only falls back on null (or a missing value), while ?: falls back on any falsy value, so 0, "", and "0" all trigger the fallback. Reach for ?? when you mean “if it is set,” and ?: when you mean “if it is truthy.”

Your Turn

<?php
$number = 4;

<?php
$number = 4;
if ($number % 2 === 0) {
    echo "even";
} else {
    echo "odd";
}

Conditionals let your code choose once. Next you will learn loops, which let it repeat an action as many times as you need.