PHP 7.1.0 Released

Arithmetic Operators

Remember basic arithmetic from school? These work just like those.

Arithmetic Operators
Example Name Result
+$a Identity Conversion of $a to int or float as appropriate.
-$a Negation Opposite of $a.
$a + $b Addition Sum of $a and $b.
$a - $b Subtraction Difference of $a and $b.
$a * $b Multiplication Product of $a and $b.
$a / $b Division Quotient of $a and $b.
$a % $b Modulo Remainder of $a divided by $b.
$a ** $b Exponentiation Result of raising $a to the $b'th power. Introduced in PHP 5.6.

The division operator ("/") returns a float value unless the two operands are integers (or strings that get converted to integers) and the numbers are evenly divisible, in which case an integer value will be returned. For integer division, see intdiv().

Operands of modulo are converted to integers (by stripping the decimal part) before processing. For floating-point modulo, see fmod().

The result of the modulo operator % has the same sign as the dividend — that is, the result of $a % $b will have the same sign as $a. For example:

<?php

echo (3)."\n";           // prints 2
echo (% -3)."\n";          // prints 2
echo (-3)."\n";          // prints -2
echo (-% -3)."\n";         // prints -2

?>

See also the manual page on Math functions.

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User Contributed Notes 10 notes

up
38
Jonathon Reinhart
10 years ago
A very simple yet maybe not obvious use of the modulus (%) operator is to check if an integer is odd or even.
<?php
 
if (($a % 2) == 1)
  { echo
"$a is odd." ;}
  if ((
$a % 2) == 0)
  { echo
"$a is even." ;}
?>

This is nice when you want to make alternating-color rows on a table, or divs.

<?php
 
for ($i = 1; $i <= 10; $i++) {
    if((
$i % 2) == 1//odd
     
{echo "<div class=\"dark\">$i</div>";}
    else  
//even
     
{echo "<div class=\"light\">$i</div>";}
   }
?>
up
15
info at sima-pc dot com
12 years ago
Note that operator % (modulus) works just with integers (between -214748348 and 2147483647) while fmod() works with short and large numbers.

Modulus with non integer numbers will give unpredictable results.
up
7
arjini at gmail dot com
12 years ago
When dealing purely with HTML, especially tables, or other things in "grids"  the modulous operator is really useful for splitting up the data with a seperator.

This snippet reads any gif files from the directory the script is in, prints them out and puts in a break every 5th image.

<?php
    $d
= dir('./');
   
$i = 0;
    while(
false !== ($e = $d->read())){
        if(
strpos($e,'.gif')){
            ++
$i;
            echo
'<img src="'.$e.'"/>'.chr(10);
            if(!(
$i%5))
                echo
'<br/>';
        }
    }
?>

For tables just put </tr><tr> in place of the break.
up
0
lmc at trendicy dot com
2 years ago
If you are running a php version older than 5.6, you can calculate $a ** $b by using exp($b*log($a))
up
-2
Dominik Buechler
1 year ago
In addition to Jonathan's comment, there is a way simpler way to determine if an integer is even or not:

<? $odd = $i % 2; ?>
or
<? $even = !($i % 2); ?>

This works because a modulo division by 2 will always return either 0 or the rest 1. Since those are valid boolean values you can just invert them by adding a prefixed ! if wanted.
up
-2
TheWanderer
8 years ago
It is worth noticing that when working with large numbers, most noticably using the modulo operator, the results depend on your CPU architecture. Therefore, running a decent 64-bit machine will be to your advantage in case you have to perform complex mathematical operations. Here is some example code - you can compare its output on x86 and x86_64 machines:
<?php
/* tested under PHP 5.2.6-1 with Suhosin-Patch 0.9.6.2 (cli) on both i386 and amd64, Debian lenny/sid */
$a = 2863311530;
$b = 256;
$c = $a % $b;
echo
"$c <br />\n";
echo (
2863311530 % 256)." <br />\n"; /* directly with no variables, just to be sure */
?>

The code is expected to produce '170' if working correctly (try it in spreadsheet software).
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-7
Andrew
3 years ago
The % operator doesn't behave as many people with a maths background would expect, when dealing with negative numbers. For example, -1 mod 8 = 7, but in PHP, -1 % 8 = -1.

The following function has the expected behaviour:

function mod($a, $n) {
    return ($a % $n) + ($a < 0 ? $n : 0);
}

mod(-1, 8) returns 7 as expected.
up
-10
calmarius at atw dot hu
8 years ago
Be careful when using % with large numbers.

The code:

<?php
   
echo 3333333333 % 3
?>

puts out -1 instead of zero!

(Due to the overflow)
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-22
php at richardneill dot org
5 years ago
For larger numbers (above PHP_INT_MAX), use fmod() rather than %.
The other operators (+-*/) work correctly with floats and integer overflow, but % uses integer wrap. Eg.

<?php
var_dump
(0xffffffff % 2);
//Prints  int(-1)   which is WRONG

var_dump(intval(fmod(0xffffffff,2)));
//Prints int(1)   which is the right answer
?>

(The reason this matters is that PHP's float is actually a double, and can accurately represent integers up to 52-bits, even on 32-bit systems)
up
-17
glenn at benge dot co dot nz
12 years ago
a real simple method to reset an integer to a the next lowest multiple of a divisor

$startSeq = $startSeq - ($startSeq % $entriesPerPage);

if $startSeq was already a multiple, then " $startSeq % $entriesPerPage " will return 0 and $startSeq will not change.
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