What is the simplest most basic way to find out if a number/variable is odd or even in PHP? Is it something to do with mod?
I've tried a few scripts but.. google isn't delivering at the moment.
You were right in thinking mod was a good place to start. Here is an expression which will return true if $number is even, false if odd:
$number % 2 == 0
Works for every integerPHP value, see as well Arithmetic OperatorsPHP.
Example:
$number = 20;
if ($number % 2 == 0) {
print "It's even";
}
Output:
It's even
Yes using the mod
$even = ($num % 2 == 0);
$odd = ($num % 2 != 0);
Another option is a simple bit checking.
n & 1
for example:
if ( $num & 1 ) {
//odd
} else {
//even
}
All even numbers divided by 2 will result in an integer
$number = 4;
if(is_int($number/2))
{
echo("Integer");
}
else
{
echo("Not Integer");
}
(bool)($number & 1)
or
(bool)(~ $number & 1)
I did a bit of testing, and found that between mod, is_int and the &-operator, mod is the fastest, followed closely by the &-operator. is_int is nearly 4 times slower than mod.
I used the following code for testing purposes:
$number = 13;
$before = microtime(true);
for ($i=0; $i<100000; $i++) {
$test = ($number%2?true:false);
}
$after = microtime(true);
echo $after-$before." seconds mod<br>";
$before = microtime(true);
for ($i=0; $i<100000; $i++) {
$test = (!is_int($number/2)?true:false);
}
$after = microtime(true);
echo $after-$before." seconds is_int<br>";
$before = microtime(true);
for ($i=0; $i<100000; $i++) {
$test = ($number&1?true:false);
}
$after = microtime(true);
echo $after-$before." seconds & operator<br>";
The results I got were pretty consistent. Here's a sample:
0.041879177093506 seconds mod
0.15969395637512 seconds is_int
0.044223070144653 seconds & operator
//for numbers n [0,1,2,3,4....]
if((n+2)%2==1) {
//odd
}else {
//even
}
Zero is an even number. In other words, its parity—the quality of an integer being even or odd—is even. The simplest way to prove that zero is even is to check that it fits the definition of "even": it is an integer multiple of 2, specifically 0 × 2. As a result, zero shares all the properties that characterize even numbers: 0 is divisible by 2, 0 is surrounded on both sides by odd numbers, 0 is the sum of an integer (0) with itself, and a set of 0 objects can be split into two equal sets. from http://en.wikipedia.org/wiki/Parity_of_zero
Another option is to check if the last digit is an even number :
$value = "1024";// A Number
$even = array(0, 2, 4, 6, 8);
if(in_array(substr($value, -1),$even)){
// Even Number
}else{
// Odd Number
}
Or to make it faster, use isset() instead of array_search :
$value = "1024";// A Number
$even = array(0 => 1, 2 => 1, 4 => 1, 6 => 1, 8 => 1);
if(isset($even[substr($value, -1)]){
// Even Number
}else{
// Odd Number
}
Or to make it more faster (beats mod operator at times) :
$even = array(0, 2, 4, 6, 8);
if(in_array(substr($number, -1),$even)){
// Even Number
}else{
// Odd Number
}
Here is the time test as a proof to my findings.
I am making an assumption that there is a counter already in place. in $i which is incremented at the end of a loop, This works for me using a shorthand query.
$row_pos = ($i & 1) ? 'odd' : 'even';
So what does this do, well it queries the statement we are making in essence $i is odd, depending whether its true or false will decide what gets returned. The returned value populates our variable $row_pos
My use of this is to place it inside the foreach loop, right before i need it, This makes it a very efficient one liner to give me the appropriate class names, this is because i already have a counter for the id's to make use of later in the program. This is a brief example of how i will use this part.
<div class='row-{$row_pos}'> random data <div>
This gives me odd and even classes on each row so i can use the correct class and stripe my printed results down the page.
The full example of what i use note the id has the counter applied to it and the class has my odd/even result applied to it.:
$i=0;
foreach ($a as $k => $v) {
$row_pos = ($i & 1) ? 'odd' : 'even';
echo "<div id='A{$i}' class='row-{$row_pos}'>{$v['f_name']} {$v['l_name']} - {$v['amount']} - {$v['date']}</div>
";
$i++;
}
in summary, this gives me a very simple way to create a pretty table.
This code checks if the number is odd or even in PHP. In the example $a is 2 and you get even number. If you need odd then change the $a value
$a=2;
if($a %2 == 0){
echo "<h3>This Number is <b>$a</b> Even</h3>";
}else{
echo "<h3>This Number is <b>$a</b> Odd</h3>";
}
PHP is converting null and an empty string automatically to a zero. That happens with modulo as well. Therefor will the code
$number % 2 == 0 or !($number & 1)
with value $number = '' or $number = null result in true. I test it therefor somewhat more extended:
function testEven($pArg){
if(is_int($pArg) === true){
$p = ($pArg % 2);
if($p== 0){
print "The input '".$pArg."' is even.<br>";
}else{
print "The input '".$pArg."' is odd.<br>";
}
}else{
print "The input '".$pArg."' is not a number.<br>";
}
}
The print is there for testing purposes, hence in practice it becomes:
function testEven($pArg){
if(is_int($pArg)=== true){
return $pArg%2;
}
return false;
}
This function returns 1 for any odd number, 0 for any even number and false when it is not a number. I always write === true or === false to let myself (and other programmers) know that the test is as intended.
$before = microtime(true);
$n = 1000;
$numbers = range(1,$n);
$cube_numbers = array_map('cube',$numbers);
function cube($n){
$msg ='even';
if($n%2 !=0){
$msg = 'odd';
}
return "The Number is $n is ".$msg;
}
foreach($cube_numbers as $cube){
echo $cube . "<br/>";
}
$after = microtime(true);
echo $after-$before. 'seconds';
While all of the answers are good and correct, simple solution in one line is:
$check = 9;
either:
echo ($check & 1 ? 'Odd' : 'Even');
or:
echo ($check % 2 ? 'Odd' : 'Even');
works very well.
Try this,
$number = 10;
switch ($number%2)
{
case 0:
echo "It's even";
break;
default:
echo "It's odd";
}
//checking even and odd
$num =14;
$even = ($num % 2 == 0);
$odd = ($num % 2 != 0);
if($even){
echo "Number is even.";
} else {
echo "Number is odd.";
}
Try this one with #Input field
<?php
//checking even and odd
echo '<form action="" method="post">';
echo "<input type='text' name='num'>
";
echo "<button type='submit' name='submit'>Check</button>
";
echo "</form>";
$num = 0;
if ($_SERVER["REQUEST_METHOD"] == "POST") {
if (empty($_POST["num"])) {
$numErr = "<span style ='color: red;'>Number is required.</span>";
echo $numErr;
die();
} else {
$num = $_POST["num"];
}
$even = ($num % 2 == 0);
$odd = ($num % 2 != 0);
if ($num > 0){
if($even){
echo "Number is even.";
} else {
echo "Number is odd.";
}
} else {
echo "Not a number.";
}
}
?>