Odd and Even Numbers in PHP

To find if a number is odd or even you can use one of two operators.

The modulo operator (% in PHP) can be used to calculate the remainder of the value divided by 2. This gives a value of 0 for even numbers and a value of 1 for odd numbers. This can be used in an if statement as 0 will equate to false and 1 will equate to true.

$value = 10;
if ($value % 2) {
  echo '$value is odd';
} else {
  echo '$value is even';
}

The second method is to use the & (AND) operator with the number 1. This will perform a bitwise calculation on the number and 1, returning 0 if the number is even and 1 if the number is false. So using the same if statement logic as before we can write.

$value = 10;
if ($value & 1) {
  echo '$value is odd';
} else {
  echo '$value is even';
}

This method gives better performance than using modulo as it uses bitwise calculations that are native to computers.

Finally, you can use the is_long() function to see if the value you return from the division of the number by 2 has a remainder. This is a slightly longer (and more resource intensive) way of doing it than using modulo, but it works.

var_dump(is_long(4/2)); // prints bool(true)
var_dump(is_long(3/2)); // prints bool(false)