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Remember basic arithmetic from school? These work just
like those.
Table 15-2. Arithmetic Operators | Example | Name | Result |
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| -$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 | Modulus | Remainder of $a divided by $b. |
The division operator ("/") returns a float value anytime,
even if the two operands are integers (or strings that get
converted to integers).
Note:
Remainder $a % $b is negative for negative
$a.
See also the manual page on
Math functions.
User Contributed Notes
Arithmetic Operators
rz at daimi dot au dot dk
04-Apr-2005 07:04
This is a really simple observation.
There is no integer division operator. But if you need to divide by a power of 2, you can use the right-shift operator instead. 257/32 gives 8.03125, but 257>>5 gives 8.
areshankar at gmail dot com
17-Mar-2005 04:40
Most of the mail services/bulletin boards display the time when the message was posted or the mail was received in the form - 3 days ago, 15 mins ago etc.
Here is a nifty little PHP function which does the same by basically combining the usage of "/" and "%" operators.
You need to pass the unix timestamp of the time when the message was posted to the function.
function intervalCalc($postedtime)
{
$now = time();
$interval_secs = $now - $postedtime;
if ($interval_secs > 86400)
{
$interval = (($interval_secs - ($interval_secs%86400))/86400);
$interval.= " days ago";
}
elseif ($interval_secs > 3600)
{
$interval = ($interval_secs - ($interval_secs%3600)/3600);
$interval.= " hours ago";
}
elseif ($interval_secs > 60)
{
$interval = ($interval_secs - ($interval_secs%60)/60);
$interval.= " minutes ago";
}
return $interval;
}
sputnik13 at gmail dot com
13-Feb-2005 08:49
I just had to make a comment about gilthans' use of the bitwise xor operator (^)... I'm guessing from the line if(($x < 0 ^ $y < 0) && $x != 0) that he wants to verify that only x or only y is less than 0 AND x != 0... Bitwise operators should not be used for truth values like this, that's what xor is for.
justin at koivi dot com
25-Jan-2005 03:08
A note about the documentation on this page that I found while teaching a PHP class:
The above statment: "The division operator ("/") returns a float value anytime, even if the two operands are integers (or strings that get converted to integers)." is NOT TRUE.
Take the following:
<?php
$a=5;
$b=10;
$c=$b/$a;
$d=10/5;
var_dump($c);
var_dump($d);
var_dump($b/$a);
var_dump(10/5);
?>
All 4 instances will print "int(2)"
Therefore, the division operator "/" returns an integer value if the numbers are evenly divisible AND they are both integers (or strings that have been converted to integer values).
no at email dot com
13-Jan-2005 03:08
If you need "div" function like in pascal ( 123 div 10 == 12) you can try this:
$number "div" 10 = ($number-($number % 10)) / 10;
jphansen at uga dot edu
06-Jan-2005 12:12
If the second operand of modulus is of a precision type, modulus will return a boolean instead of a numeric type.
gilthans at gmail dot com
20-Dec-2004 03:13
Me and a few friends were talking about how math works in coding languages, and after a while of discussion, we started wondering how does the sqrt() function works, and how does the division work, using only addition, substraction and multiplication (because that could be easily done using only addition).
I have best knowledge in PHP, so I had my shot at division, and a while of testing proved that my code works. I'm posting this here for the curious, even though the normal PHP division works 7 times faster, so I think there is some way of making my code more efficient.
divide($x, $y, $a, 0) is similar to number_format($x/$y, $a);, and divide($x, $y, $a, 1) is similar to Array(floor($x/$y), $x%$y).
<?php
function divide($x, $y, $a=6, $z=false){
$t = '';
if($y == 0)
return 0;
if(($x < 0 ^ $y < 0) && $x != 0)
$t = '-';
$x = abs($x);
$y = abs($y);
$in = 0;
while(($in+1)*$y <= $x)
$in++;
$r = $x-($in*$y);
if($z)
return Array($in, $r);
$d = '';
$c = 0;
while($r != 0 && $c < $a){
list($u, $r) = divide($r*10, $y, $a, 1);
$c++;
if($c >= $a){
$b = divide($r*10, $y, $a, 1);
$u += ($b[0] > 4) ? 1 : 0;
}
$d .= $u;
}
return intval($t.$in.(($d != '') ? ".".$d : ""));
}
?>
adam.pippin at accesscomm dot ca
02-Dec-2004 03:15
To factor a number:
<?php
function factornumber($number)
{
for ($i=1; $i<=($number/2); $i++)
{
if ($number % $i == 0)
{
echo "$i * ".($number/$i)." = $number\n";
}
}
}
factornumber(50);
?>
That script outputs:
1 * 50 = 50
2 * 25 = 50
5 * 10 = 50
10 * 5 = 50
25 * 2 = 50
As you may notice, it makes no attempts at removing duplicates (eg: 5*10 and 10*5), although it would be trivial to make it do so.
glenn at benge dot co dot nz
06-Oct-2004 01:28
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.
arjini at gmail dot com
08-Sep-2004 11:48
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(!($i%5))
echo '<br/>';
}
}
?>
For tables just put </tr><tr> in place of the break.
csaba at alum dot mit dot edu
16-May-2004 07:32
The function below is not a replacement for http://php.net/fmod Rather, it is the classic (mathematician's) modulo where the resultant value is always non-negative, in the range [0,$base). For example, mod(-9,7) => 5. When both arguments are integers, you get the classic notion of the % operator.
function mod($num, $base) {
return ($num - $base*floor($num/$base)); }
Csaba Gabor
info at sima-pc dot com
01-May-2004 04:48
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.
php AT internethoofdkantoor.nl
12-Jan-2004 06:15
For the mathematicians among us:
The mod operator % works a bit differently than in mathematics (e.g. in group theory), in that negative remainders aren't represented by their positive equivalence classes, as is common in mathematics.
An example:
-1%7 returns -1, instead of 6.
it depends a bit on how you interpret 'remainder of a division', i.e. if you want the remainder to be always positive.
soren at byu dot edu
19-Nov-2003 09:49
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)
darnell at uga dot edu
28-Oct-2003 09:57
Also, when automatically converting floats to integers, PHP truncates them rather than rounding. So in the previous note, 2.4 gets truncated to 2 before the modulus operator is applied.
todd at magnifisites dot com
16-Oct-2003 06:22
There isn't much detail in the PHP Manual regarding the PHP modulus operator (%). It seems as though the PHP modulus operator (%) works on integer operands. If PHP operates like Perl, then the modulus operator (%) converts its operands to integers before finding the remainder according to integer division. Testing seems to prove the theory:
<?php
$dividend = 7;
$divisor = 2.4;
print $dividend%$divisor; print fmod($dividend, $divisor); ?>
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Operators