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Оператор присвоения Операторы

Last updated: Fri, 26 Jan 2007

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# Арифметические операторы

Помните школьные основы арифметики? Описанные ниже операторы работают так же.

Таблица 15-2. Арифметические операции

Пример | Название | Результат
--- | --- | ---
-$a | Отрицание | Смена знака $a.
$a + $b | Сложение | Сумма $a и $b.
$a - $b | Вычитание | Разность $a и $b.
$a * $b | Умножение | Произведение $a и $b.
$a / $b | Деление | Частное от деления $a на $b.
$a % $b | Деление по модулю | Целочисленный остаток от деления $a на $b.

Операция деления ("/") всегда возвращает вещественный тип, даже если оба значения были целочисленными (или строками, которые преобразуются в целые числа).

> Замечание: Остаток `$a % $b` будет негативным, для негативных значений `$a`.

Также вы можете ознакомиться с разделом документации Математические функции.

add a note User Contributed Notes
Арифметические операторы
gilthansREMOVEME at gmail dot com
15-Dec-2006 07:43
`1) About integer division: here's a function that neatly solves this. It is somewhat slower than normal division, but is failsafe.
<?php
function integer_divide($x, $y){
//Returns the integer division of $x/$y.
$t = 1;
if($y == 0 || $x == 0)
return 0;
if($x < 0 XOR $y < 0) //Mistaken the XOR in the last instance...
$t = -1;
$x = abs($x);
$y = abs($y);
$ret = 0;
while(($ret+1)*$y <= $x)
$ret++;
return $t*$ret;
}
?>
2) adam.pippin noted about number factoration, however the function returns alot of sequences in text form. This one returns an Array with all the factored numbers of a number. For example, factor(50) would return Array(2, 5, 5).
<?php
function factor($n){
$ret = Array();
$i = 2;
$m = $n/2;
while($i <= $m){
if(!($n%$i))
$ret = array_merge($ret, factor($i), factor($n/$i));
if($i%2)
$i+=2; //$i is impair
else
$i++;
//Ideally, you'd only run through prime numbers, but there is no way to tell what is the next prime number; we can be sure, however, that the pair ones aren't prime.
$m = $n/$i; //If $n isn't divisible by $i, it be assumed it isn't divisible by any number bigger than $n/$i, and if it is divisible by $i, $n/$i is already put in. The derivation for this isn't too complex. This drastically reduces the number of numbers we have to go through during the factoration.
}
if(empty($ret))
return Array($n);
return $ret;
}
?>
This has only been tested for integers, factoration for floats should include some way to identify the divisor.
Hope this saves someone some headaches.`
jon_rhoades at yahoo dot com
27-Nov-2006 04:48
`Jonathon Reinhart's neat little function to find out if a value is odd or even doesn't work for floats (this might possibly arithmetically correct but causes the following problem) eg
<?php
12.23 % 2 = 0 not 1
?>
So if you need to find out if the fraction part of a float is odd or even try:
<?php
if (($a /2) != (floor($a /2))){
echo "$a is odd." ;
}
if (($a /2) == (floor($a /2))){
echo "$a is even." ;
}
?>`
sean at somethinglikemedia dot com
06-Nov-2006 04:02
`An easier way of doing alternating row colors is just setting the first row color outside of your loop, calling your loop, and then calling the class or hex code into a single spot, rather than re-creating the entire div both times.
Something like this:
<?php
$class = "odd";
for ($i = 1; $i <= 10; $i++) {
echo "<div class=\"".$class."\">".$i."</div>";
if ($class == "odd") { $class = "even"; } else { $class = "odd"; }
}
?>`
Jonathon Reinhart
16-Oct-2006 02:11
`A very simple yet maybe not obvious use of the modulus (%) operator is to check if an integer is odd or even.
<?php
if (($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>";}
}
?>`
mdirks at gulfstreamcoach dot com
13-Sep-2006 07:01
`Quote from TChan's post:
"...But if you're dealing with ints anyway, (a-a%b)/b has no function calls and returns an int, while floor() always returns a float."
It *explicitly* says in the documentation that the division operator *always* returns a float value *regardless* of the types of the operands. While you may get the "integer part" of the number that way you will technically not get an integer. PHP may not be too strongly typed for the most part, but it's important to make the distinction.
"... if the 'fractional part' of $a/$b is close to 1, then it can round up, and floor($a/$b) will be larger than it should be."
Actually I think you meant *smaller*, not larger... the reason floor($a/$b) isn't absolutely equatable with the integer division of $a and $b is explained mainly at http://us3.php.net/float . By the look of things, any number with a loss of precision will be truncated instead of rounded. This would at least make sense in the big picture since truncation is more consistant than rounding.`
T Chan
19-Aug-2006 09:28
`Please note that floor($a/$b) is not the same as integer division. if the 'fractional part' of $a/$b is close to 1, then it can round up, and floor($a/$b) will be larger than it should be. The example is a bit contrived though (and printf doesn't print enough digits).
<?php printf("%f\n",$a = 9007199254740991); // 9007199254740991.000000
printf("%f\n", $b = $a * 3.0); //27021597764222970.000000, the actual value stored ends in 2 while the true value ends in 3
printf("%f\n", $b/$a - 3.0); //0.000000
printf("%f\n", $b - 2*$a - $a); //-1.000000
printf("%f\n",fmod($b,$a)); //9007199254740990.000000 fmod agrees too
?>
Admittedly it's a bit 'specially-crafted', but it just goes to show. I believe it does work for integers that can be exactly represented in FP. But if you're dealing with ints anyway, (a-a%b)/b has no function calls and returns an int, while floor() always returns a float.`
Ulf Wostner
05-Aug-2006 12:13
`# There are several natural ways to define the mod operator for integers.
# Requirement: If mod(k, m) = r, then k and r differ by a multiple of m.
# For m=7, think days-of-the-week. Both mod(13, 7) = 6 and mod(13, 7) = -1
# satisfy the requirement. Six days from today, or one day ago, are the same DOW.
# There are several natural ways to define the mod operator for integers.
# Requirement: If mod(k, m) = r, then k and r differ by a multiple of m.
# For m=7, think days-of-the-week. Both mod(13, 7) = 6 and mod(13, 7) = -1
# satisfy the requirement. Six days from today, or one day ago, are the same DOW.
# Here are four mod operators:
# 1. mod_php.
# Same as the built-in PHP function, so mod_php($k,$m) == ($k % $m).
# A negative value might jolt a programmer using it for array index.
function mod_php($k, $m) {return $k % $m; }
# 2. Standard math definition.
# Nice. But, if for some reason m is negative, be prepared for negative values.
function mod_math($k, $m) { return ($k - $m * floor($k/$m)); }
# 3. Smallest absolute value.
# Sometimes convenient for large integers, making good use of the sign-bit.
# Also, for mere humans, "-2 months from May", might be easier than "10 months from May".
function mod_min($k, $m) {
$r = mod_pos($k, $m);
if($r > abs($m)/2) $r -= abs($m);
return $r;
}
# 4. Smallest non-negative value.
# Maybe closest to the concept that mod is the remainder when dividing $k by $m.
function mod_pos($k, $m) { return ($k - abs($m) * floor($k/abs($m))); }
# This table compares the four functions.
k m mod_php mod_math mod_min mod_pos
18 7 4 4 -3 4
17 7 3 3 3 3
16 7 2 2 2 2
-16 7 -2 5 -2 5
-17 7 -3 4 -3 4
-18 7 -4 3 3 3
18 -7 4 -3 -3 4
17 -7 3 -4 3 3
16 -7 2 -5 2 2
-16 -7 -2 -2 -2 5
-17 -7 -3 -3 -3 4
-18 -7 -4 -4 3 3`
bxm AT cs d0t nott d0t ac d0t uk
05-Jun-2006 04:06
`An implementation of the classical modulus operator (as in mathematics or Java). An alternative to the one given below, which was more elegant. This implementation maybe more efficient?
// Computes...
// Mathematics: $a (mod $b)
// Java: $a % $b
function modulus( $a, $b )
{
if( $a < 0 )
{
return $b - ( abs( $a ) % $b );
}
else
{
return $a % $b;
}
}`
andr3a at 3site dot it
05-Jun-2006 05:14
`[ops ... wrong example :D]
just a note about module, it works only with integers.
<?php
$a = pow(2, 31);
$b = ($a / 2) - 1;
echo implode('<br />', array(
$a + $b, // OK => 3221225472
$a - $b, // OK => 1073741825
$a * $b, // OK => 2.3058430070662E+018
$a / $b, // OK => 2.0000000018626
$a % $b // WTF ? => -2
));
?>
maybe bc_mod with a string cast should be a solution
bc_mod((string)pow(2,31), (pow(2,31)/2)-1)`
shmee35 at hotmail dot com
14-Dec-2005 03:00
`Note that constructs which evaluate to 0 (such as empty strings, false, or an explicit NULL) will be treated as 0 in a arithmetic operation. Therefore:
<?php
echo 5*"", '<br>';
echo 5+false, '<br>';
echo 5/NULL, '<br>';
?>
Will produce:
0
5
Warning: Division by zero`
pww8 at cornell dot edu
17-Aug-2005 02:25
`It appears floating-point infinity (INF) is not returned from divide by zero (in PHP 5.0.0). Instead a warning is given and Boolean FALSE is returned.
I searched the various manuals and did not find relevant explanation, so am adding this.`
Gemini6Ice
13-Aug-2005 03:59
`For integer division, just use floor($a / $b).`
rz at daimi dot au dot dk
04-Apr-2005 05:04
`This is a really simple observation.
There is no integer division operator. But if you need to divide by a power of 2, you can use the right-shift operator instead. 257/32 gives 8.03125, but 257>>5 gives 8.`
areshankar at gmail dot com
17-Mar-2005 02:40
`Most of the mail services/bulletin boards display the time when the message was posted or the mail was received in the form - 3 days ago, 15 mins ago etc.
Here is a nifty little PHP function which does the same by basically combining the usage of "/" and "%" operators.
You need to pass the unix timestamp of the time when the message was posted to the function.
function intervalCalc($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 $interval;
}`
sputnik13 at gmail dot com
13-Feb-2005 06:49
`I just had to make a comment about gilthans' use of the bitwise xor operator (^)... I'm guessing from the line if(($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 01:08
`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 01:08
`If you need "div" function like in pascal ( 123 div 10 == 12) you can try this:
$number "div" 10 = ($number-($number % 10)) / 10;`
jphansen at uga dot edu
06-Jan-2005 10:12
`If the second operand of modulus is of a precision type, modulus will return a boolean instead of a numeric type.`
gilthans at gmail dot com
20-Dec-2004 01:13
`Me and a few friends were talking about how math works in coding languages, and after a while of discussion, we started wondering how does the sqrt() function works, and how does the division work, using only addition, substraction and multiplication (because that could be easily done using only addition).
I have best knowledge in PHP, so I had my shot at division, and a while of testing proved that my code works. I'm posting this here for the curious, even though the normal PHP division works 7 times faster, so I think there is some way of making my code more efficient.
divide($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){
// returns $x/$y
$t = '';
if($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 != '') ? ".".$d : ""));
}
?>`
adam.pippin at accesscomm dot ca
02-Dec-2004 01:15
`To factor a number:
<?php
function factornumber($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
05-Oct-2004 11:28
`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 09:48
`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(!($i%5))
echo '<br/>';
}
}
?>
For tables just put </tr><tr> in place of the break.`
csaba at alum dot mit dot edu
16-May-2004 05:32
`The function below is not a replacement for http://php.net/fmod Rather, it is the classic (mathematician's) modulo where the resultant value is always non-negative, in the range [0,$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 02:48
`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 04:15
`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 07:49
`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 07:57
`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 04:22
`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; // prints 1
print fmod($dividend, $divisor); // prints 2.2
?>`
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Оператор присвоения Операторы

Last updated: Fri, 26 Jan 2007
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