What you will learn
- Define and call functions with parameters and return values.
- Explain parameters versus arguments and return versus echo.
- Use local scope and avoid unnecessary globals.
- Add scalar type declarations and return types where they clarify contracts.
The code from this chapter
Type these programs yourself. The predictions below are the exercises; the explanations are in the book.
6.1 Why Functions Matter
Type this into a file, predict the output, then run it.
<?php
declare(strict_types=1);
function celsiusToFahrenheit(float $celsius): float
{
return ($celsius * 9 / 5) + 32;
}
echo celsiusToFahrenheit(0) . PHP_EOL;
echo celsiusToFahrenheit(100) . PHP_EOL;6.2 Scope and Side Effects
Type this into a file, predict the output, then run it.
<?php
declare(strict_types=1);
function makeTotal(): int
{
$total = 10;
return $total;
}
echo makeTotal() . PHP_EOL;
var_dump(isset($total));6.3 Type Declarations and Defaults
Type this into a file, predict the output, then run it.
<?php
declare(strict_types=1);
function invoiceLine(string $item, int $quantity = 1, float $unitPrice = 0.0): string
{
return $item . " x" . $quantity . " = " . number_format($quantity * $unitPrice, 2);
}
echo invoiceLine("Notebook") . PHP_EOL;
echo invoiceLine("Notebook", unitPrice: 4.50, quantity: 3) . PHP_EOL;Type this one as well, and predict it before you run it.
<?php
// This file has no declare(strict_types=1) line, on purpose.
function isPassing(int $score): bool
{
return $score >= 60;
}
var_dump(isPassing("72"));TPRM Lab 6.1: Area as a Returning Function
Type this into a file, predict the output, then run it.
<?php
declare(strict_types=1);
function rectangleArea(float $width, float $height): float
{
return $width * $height;
}
$area = rectangleArea(7, 3);
echo "Area: " . $area . PHP_EOL;TPRM Lab 6.2: A Default Parameter
Type this into a file, predict the output, then run it.
<?php
declare(strict_types=1);
function greet(string $name, string $greeting = "Hello"): string
{
return $greeting . ", " . $name . "!";
}
echo greet("Maya") . PHP_EOL;
echo greet("Noah", "Welcome") . PHP_EOL;