9. PHP Numbers and Math

What you will learn

• Integers and floats
• Rounding and formatting
• Useful math functions
• Random numbers, and checking numeric input

Integers and floats

An int is a whole number and a float has a decimal part. PHP chooses the type from the value.

<?php
var_dump(7);
var_dump(7.0);
var_dump(7 / 2);
var_dump(7 % 2);
var_dump(2 ** 3);
var_dump(intdiv(7, 2));

int(7)
float(7)
float(3.5)
int(1)
int(8)
int(3)

% gives the remainder, ** is the power, and intdiv() divides and drops the remainder.

Rounding

<?php
echo round(4.6) . "<br>";
echo round(3.14159, 2) . "<br>";
echo ceil(4.1) . "<br>";
echo floor(4.9);

More math functions

<?php
echo abs(-7) . "<br>";
echo max(3, 9, 5) . "<br>";
echo min(3, 9, 5) . "<br>";
echo sqrt(81) . "<br>";
echo pow(2, 10) . "<br>";
echo round(pi(), 4);

Formatting for display

number_format() adds thousands separators and fixes decimals. It returns text, so use it for showing numbers, not for calculating.

<?php
$price = 1234567.891;

echo number_format($price) . "<br>";
echo number_format($price, 2) . "<br>";
echo number_format($price, 2, ",", ".");

Random numbers

random_int($min, $max) gives a secure random whole number, both ends included. rand() is older and not secure. Use random_int() for anything that matters, such as tokens.

<?php
echo "You rolled: " . random_int(1, 6);

Float accuracy

Computers store decimals in binary, so some sums are very slightly off, in every language.

<?php
var_dump(0.1 + 0.2 == 0.3);
var_dump(abs((0.1 + 0.2) - 0.3) < 0.00001);

bool(false)
bool(true)

Compare floats with a small tolerance. For money, many developers store whole cents as integers.

Checking numeric input

Form values are strings. Check them before calculating.

<?php
var_dump(is_numeric("42"));
var_dump(is_numeric("4.2e1"));
var_dump(is_numeric("42abc"));
var_dump(is_numeric(""));
var_dump(filter_var("42", FILTER_VALIDATE_INT));
var_dump(filter_var("4.5", FILTER_VALIDATE_INT));

bool(true)
bool(true)
bool(false)
bool(false)
int(42)
bool(false)

filter_var() with FILTER_VALIDATE_INT returns the integer, or false when the text is not a whole number.

Common mistakes

• Comparing floats with ==.
• Using number_format() output in further calculations.
• Using rand() for security.
• Dividing by zero, which throws an error in PHP 8.
• Trusting form input to be numeric.

<?php
$price = 19.99;
$tax_rate = 0.2;

$total = $price * (1 + $tax_rate);
echo number_format($total, 2);

Summary

• PHP has int and float, with round, ceil, floor, abs, max, and min.
• number_format() is for display only.
• Use random_int() and validate numeric input.