PHP Operadores ~ Veklas

Lembra-se da aritmética básica da escola? Estes operadores funcionam exatamente como aqueles.

Operadores Aritméticos
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` e `$b`.
$a % $b	Módulo	Resto de `$a` dividido por `$b`.
$a ** $b	Exponencial	Resultado de `$a` elevado a `$b`. Introduzido no PHP 5.6.

O operador de divisão ("/") sempre retorna um valor com ponto flutuante, a não ser que os dois operandos sejam inteiros (ou strings que são convertidas para inteiros) e números inteiramente divisíveis, nesse caso um inteiro é retornado.

Operandos de módulo são convertidos para inteiros (removendo a parte decimal) antes do processamento.

O resultado do operador de módulo % tem o mesmo sinal do dividendo — ou seja, o resultado de $a % $b terá o mesmo sinal de $a. Exemplos:


echo (5 % 3)."\n";           // imprime 2echo (5 % -3)."\n";          // imprime 2echo (-5 % 3)."\n";          // imprime -2echo (-5 % -3)."\n";         // imprime -2
?>

Veja também a página do manual sobre funções matemáticas.

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User Contributed Notes 11 notes

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Jonathon Reinhart ¶

9 years ago

A very simple yet maybe not obvious use of the modulus (%) operator is to check if an integer is odd or even.
  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.

  for ($i = 1; $i <= 10; $i++) {
    if(($i % 2) == 1)  //odd
      {echo "

$i

;}
else //even
{echo "

$i";}
}?>

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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.

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arjini at gmail dot com ¶

11 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.

    $d = dir('./');
    $i = 0;
    while(false !== ($e = $d->read())){
        if(strpos($e,'.gif')){
            ++$i;
            echo '.$e.'"/>'.chr(10);
            if(!($i%5))
                echo '
';
        }
    }?>
For tables just put

in place of the break.

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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:
/* 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
\n";
echo (2863311530 % 256)." 
\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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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:


or


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.

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-1

lmc at trendicy dot com ¶

1 year ago

If you are running a php version older than 5.6, you can calculate $a ** $b by using exp($b*log($a))

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-1

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.

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-11

calmarius at atw dot hu ¶

8 years ago

Be careful when using % with large numbers.

The code:

    echo 3333333333 % 3
?>
puts out -1 instead of zero!

(Due to the overflow)

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-11

pww8 at cornell dot edu ¶

11 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.

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-10

glenn at benge dot co dot nz ¶

11 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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-20

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.

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)