PHP 5.4.33 Released

算术运算符

还记得学校里学到的基本数学知识吗?就和它们一样。

算术运算符
例子 名称 结果
-$a 取反 $a 的负值。
$a + $b 加法 $a$b 的和。
$a - $b 减法 $a$b 的差。
$a * $b 乘法 $a$b 的积。
$a / $b 除法 $a 除以 $b 的商。
$a % $b 取模 $a 除以 $b 的余数。

除法运算符总是返回浮点数。只有在下列情况例外:两个操作数都是整数(或字符串转换成的整数)并且正好能整除,这时它返回一个整数。

取模运算符的操作数在运算之前都会转换成整数(除去小数部分)。

取模运算符 % 的结果和被除数的符号(正负号)相同。即 $a % $b 的结果和 $a 的符号相同。例如:

<?php

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

?>

参见手册中的数学函数

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User Contributed Notes 12 notes

up
15
Jonathon Reinhart
7 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
10
arjini at gmail dot com
10 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
6
info at sima-pc dot com
10 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
3
TheWanderer
6 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).
up
2
calmarius at atw dot hu
6 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)
up
1
lmc at trendicy dot com
13 days ago
If you are running a php version older than 5.6, you can calculate $a ** $b by using exp($b*log($a))
up
0
Andrew
1 year 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
-4
pww8 at cornell dot edu
9 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.
up
-5
glenn at benge dot co dot nz
9 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.
up
-12
antickon at gmail dot com
2 years ago
not listed here is the absolutely useless unary plus.

<?php
$a
= -3;
$a = +$a;
var_dump( $a ); // int(-3)
up
-11
php at richardneill dot org
3 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
-21
hassan dot beydoun at live dot com
10 months ago
<?php

//using range function()
//$numbers = array;range = value

$numbers= range (1,100);
// foreach ($array as $value)
//{Do something with $value}
foreach ($numbers as $value)
{echo
"<p>This is number: $value</P>";}

?>
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