Precedência de Operadores
Be careful when using % with large numbers.
The code:
<?php
echo 3333333333 % 3
?>
puts out -1 instead of zero!
(Due to the overflow)
Operadores Aritméticos
Lembra-se da aritmética básica da escola? Estes operadores funcionam exatamente como aqueles.
| Exemplo | Nome | Resultado |
|---|---|---|
| -$a | Negação | Oposto de $a. |
| $a + $b | Adição | Soma de $a e $b. |
| $a - $b | Subtração | Diferença entre $a e $b. |
| $a * $b | Multiplicação | Produto de $a e $b. |
| $a / $b | Divisão | Quociente de $a por $b. |
| $a % $b | Módulo | Resto de $a dividido por $b. |
O operador de divisão ("/") sempre retorna um valor com ponto flutuante, a não ser que os dois operados seja inteiros (ou strings que são convertidas para inteiros) e numéros inteiramente divisíveis, em outro caso um inteiro é retornado.
Operandos de módulo são convertidos para inteiros (removendo a parte decimal) antes de processar.
Nota: O resto de $a % $b é negativo se $a for negativo.
Veja também a página do manual funções matemáticas.
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User Contributed Notes
Operadores Aritméticos - [10 notes]
calmarius at atw dot hu ¶
4 years ago
TheWanderer ¶
4 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).
Jonathon Reinhart ¶
6 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>";}
}
?>
antickon at gmail dot com ¶
1 year ago
not listed here is the absolutely useless unary plus.
<?php
$a = -3;
$a = +$a;
var_dump( $a ); // int(-3)
arjini at gmail dot com ¶
8 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.
info at sima-pc dot com ¶
9 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.
pww8 at cornell dot edu ¶
7 years ago
It appears floating-point infinity (INF) is not returned from divide by zero (in PHP 5.0.0). Instead a warning is given and Boolean FALSE is returned.
I searched the various manuals and did not find relevant explanation, so am adding this.
glenn at benge dot co dot nz ¶
8 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.
soren at byu dot edu ¶
9 years ago
Exponentiation doesn't use ^ or ** as you might be used to with other languages. To calculate "z equals y to the x" use:
$z = pow(y,x)
php at richardneill dot org ¶
2 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)