Checkpoint: PHP Basics

You've learned data types, strings, numbers, type juggling, constants, superglobals and null operators — let's combine them. This checkpoint is one build that exercises everything from the section at once, plus a quiz to confirm it all stuck.

Learn Checkpoint: PHP Basics in our free PHP course — a beginner-friendly interactive lesson with worked examples, a practice exercise and a quick recall.

Part of the free Php course at LearnCodingFast — hands-on lessons with examples you run in your browser, plus practice exercises and a quick quiz.

Eight types; the everyday five (string, int, float, bool, null); the falsy seven; get_debug_type .

Interpolation, trim , str_contains , substr , explode / implode , mb_* .

% , ** , round / ceil / floor , number_format , the float trap.

Implicit juggling vs explicit casts, == vs === , strict_types , filter_var .

const vs define , array & class constants, magic constants, global scope.

$_GET / $_POST / $_SERVER , validate-then-escape, ?? , ??= , ?-> .

The Build: Order Receipt Generator

Here's the brief. You're handed form-style input where every value is a string and one field ( coupon ) is missing entirely. Your job is to read it safely, validate the numbers, do the money math with a constant tax rate, and print a clean receipt. This single script touches every topic from PHP Basics. Start from the starter below; only reveal the solution once you've genuinely attempted it.

Compare this against your own attempt. The key moves: ?? defaults every read, filter_var validates the numeric strings (returning false on failure, which is why we test with === false ), constants hold the tax rate and currency, and number_format formats the money for display only.

📝 Checkpoint Quiz

Six questions spanning the whole section. Predict each answer first, then reveal it. If any surprise you, revisit the linked lesson — that's exactly what checkpoints are for.

float(5) . The / operator always returns a float, even for whole results. Use intdiv(10, 2) if you need int(5) . (See Numbers .)

Only "0.0" is truthy — it's a non-empty string that isn't exactly "0" . The other three are all in the falsy seven. (See Data Types .)

?? prints 0 (it only replaces null). ?: would print none because 0 is falsy. (See Null Operators .)

It throws a TypeError — strict types refuse to silently juggle the string into an int. (See Type Juggling .)

Because it's untrusted user input; echoing it raw enables XSS. Wrap output in htmlspecialchars() so injected markup renders as harmless text. (See Superglobals .)

Yes to reading — constants are global by nature. No to reassigning — a constant is write-once; redefining it is a fatal error. (See Constants .)

Receipt totals are off by a few cents? Remember floats aren't exact — for a learning exercise number_format(..., 2) rounds the display cleanly; in production you'd work in integer cents.

"Undefined array key 'coupon'"? You read it without ?? . Use $_POST['coupon'] ?? null .

Name shows lower-case? Chain the calls in the right order: ucwords(trim(...)) — trim first, then title-case.

Practice quiz

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