Test if number is odd or even

Question

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 integer^PHP value, see as well Arithmetic Operators^PHP.

Example:

$number = 20;
if ($number % 2 == 0) {
  print "It's even";
}

Output:

It's even

Another option is a simple bit checking.

n & 1

for example:

if ( $num & 1 ) {
  //odd
} else {
  //even
}

Yes using the mod

$even = ($num % 2 == 0);
$odd = ($num % 2 != 0);

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.

(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

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.