Operator Precedence

When an expression has several operators, PHP follows an order of priority called precedence. You know it from maths: multiplication comes before addition.

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<?php
echo 2 + 3 * 4;

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14

3 * 4 runs first, then + 2.

A simplified order, highest first

1. ** (power)
2. ++ -- and casts like (int)
3. ! (not)
4. * / %
5. + -
6. . (concatenation, since PHP 8)
7. < <= > >=
8. == != === !== <=>
9. &&
10. ||
11. ??
12. ? : (ternary)
13. = += -= and other assignments
14. and
15. xor
16. or

You do not need to memorise this. Use it when something behaves unexpectedly.

Common surprises

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3

<?php
var_dump(true || false && false);   // && is stronger than ||
var_dump((true || false) && false);

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bool(true)
bool(false)

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3
4

<?php
echo -2 ** 2;     // power is stronger than minus
echo "\n";
echo (-2) ** 2;

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2

-4
4

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2

<?php
echo "Sum: " . 1 + 2;   // in PHP 8, + comes before the dot

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Sum: 3

Same level: which side first?

Most operators with the same priority run left to right. A few run right to left: **, assignment and ??.

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3

<?php
echo 2 ** 3 ** 2 . "\n";   // 2 ** (3 ** 2)
echo 10 - 4 - 3;           // (10 - 4) - 3

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512
3

The practical rule

Add brackets whenever there is any doubt. Brackets cost nothing, and they tell the next reader exactly what you meant.

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8

<?php
$price = 100;
$discount = 20;
$tax = 18;

$total = ($price - $discount) * (1 + $tax / 100);

echo $total;

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94.4