Functions and Scope

Return Values

A function can compute a value and return it to the caller.

return `return` sends a value back to the expression that called the function.

Return Values

quantity
return_values.php
Replay: real traced execution (multi-file project)
<?php
function subtotal(int $price, int $quantity): int {
    $total = $price * $quantity;
    return $total;
}

$quantity = 3;
$amount = subtotal(7, $quantity);

echo "quantity=" . $quantity . "\n";
echo "amount=" . $amount . "\n";

<?php
function subtotal(int $price, int $quantity): int {
    $total = $price * $quantity;
    return $total;
}

$quantity = 1;
$amount = subtotal(7, $quantity);

echo "quantity=" . $quantity . "\n";
echo "amount=" . $amount . "\n";

<?php
function subtotal(int $price, int $quantity): int {
    $total = $price * $quantity;
    return $total;
}

$quantity = 5;
$amount = subtotal(7, $quantity);

echo "quantity=" . $quantity . "\n";
echo "amount=" . $amount . "\n";

  1. $quantity ← 3

    7$quantity→ 3 = 3; //@quantity=1, 58$amount = subtotal(7, $quantity3);

  2. $total ← 21

    1<?php2function subtotal(int $price7, int $quantity3): int {3    $total→ 21 = $price7 * $quantity3;4    return $total21;5}

  3. $amount ← 21

    7$quantity = 3; //@quantity=1, 58$amount→ 21 = subtotal(7, $quantity3);910echo "quantity=" . $quantity3 . "\n";11echo "amount=" . $amount21 . "\n";
    outputquantity=3
amount=21

  1. $quantity ← 1

    7$quantity→ 1 = 1;8$amount = subtotal(7, $quantity1);

  2. $total ← 7

    1<?php2function subtotal(int $price7, int $quantity1): int {3    $total→ 7 = $price7 * $quantity1;4    return $total7;5}

  3. $amount ← 7

    7$quantity = 1;8$amount→ 7 = subtotal(7, $quantity1);910echo "quantity=" . $quantity1 . "\n";11echo "amount=" . $amount7 . "\n";
    outputquantity=1
amount=7

  1. $quantity ← 5

    7$quantity→ 5 = 5;8$amount = subtotal(7, $quantity5);

  2. $total ← 35

    1<?php2function subtotal(int $price7, int $quantity5): int {3    $total→ 35 = $price7 * $quantity5;4    return $total35;5}

  3. $amount ← 35

    7$quantity = 5;8$amount→ 35 = subtotal(7, $quantity5);910echo "quantity=" . $quantity5 . "\n";11echo "amount=" . $amount35 . "\n";
    outputquantity=5
amount=35

Follow the Return

  1. quantity starts as 3.
  2. The call is subtotal(7, $quantity).
  3. Inside the function, price 7 is multiplied by quantity 3.
  4. The return value is 21.
  5. The script prints quantity=3 and amount=21. | quantity | calculation | amount | | --- | --- | --- | | 3 | 7 * 3 | 21 | | 1 | 7 * 1 | 7 | | 5 | 7 * 5 | 35 |

Exercise: return_values.php

Reproduce quantity=3 and amount=21, then use the pinned quantity variants 1 and 5 to predict amount=7 and amount=35.