Foundations

Variables

Variables store values that later expressions can reuse.

variable PHP variable names start with `$` and can store strings, numbers, arrays, and other values.

Variables

unitPrice
variables.php
Replay: real traced execution (multi-file project)
<?php
$unitPrice = 12;
$quantity = 3;
$total = $unitPrice * $quantity;

echo "unit=" . $unitPrice . "\n";
echo "total=" . $total . "\n";

<?php
$unitPrice = 8;
$quantity = 3;
$total = $unitPrice * $quantity;

echo "unit=" . $unitPrice . "\n";
echo "total=" . $total . "\n";

<?php
$unitPrice = 20;
$quantity = 3;
$total = $unitPrice * $quantity;

echo "unit=" . $unitPrice . "\n";
echo "total=" . $total . "\n";

  1. $unitPrice ← 12, $quantity ← 3, $total ← 36

    1<?php2$unitPrice→ 12 = 12; //@unitPrice=8, 203$quantity→ 3 = 3;4$total→ 36 = $unitPrice12 * $quantity3;56echo "unit=" . $unitPrice12 . "\n";7echo "total=" . $total36 . "\n";
    outputunit=12
total=36

  1. $unitPrice ← 8, $quantity ← 3, $total ← 24

    1<?php2$unitPrice→ 8 = 8;3$quantity→ 3 = 3;4$total→ 24 = $unitPrice8 * $quantity3;56echo "unit=" . $unitPrice8 . "\n";7echo "total=" . $total24 . "\n";
    outputunit=8
total=24

  1. $unitPrice ← 20, $quantity ← 3, $total ← 60

    1<?php2$unitPrice→ 20 = 20;3$quantity→ 3 = 3;4$total→ 60 = $unitPrice20 * $quantity3;56echo "unit=" . $unitPrice20 . "\n";7echo "total=" . $total60 . "\n";
    outputunit=20
total=60

Follow the Total

  1. $unitPrice starts at 12.
  2. $quantity starts at 3.
  3. $total = $unitPrice * $quantity multiplies 12 * 3.
  4. $total becomes 36.
  5. The program prints unit=12 and total=36. | unitPrice | quantity | total | | --- | --- | --- | | 8 | 3 | 24 | | 12 | 3 | 36 | | 20 | 3 | 60 |

Exercise: variables.php

Reproduce unit=12 and total=36, then try unitPrice 8 and 20 and predict each total before running it.