# Finding Even or Odd numbers with PHP

PHP does not provide any mathematical function like `is_even`

to help you check if a given integer is an `Even`

number or `Odd`

. Writing your own such function is not difficult and below are listed a number of alternatives that provide different logical solutions to do this.

1 2 3 | function is_even( $int ) { return !( ( ( int ) $int ) & 1 ); } |

What it does is first of all casts the given number to `int`

and then applies bitwise `&`

operator on `$int`

and `1`

. Bitwise `&`

operator checks for bits that are `ON`

in both of its operands `$int`

and `1`

. `1`

has just the least significant bit `ON`

, and if the same bit is `ON`

in `$int`

, the whole answer of the expression becomes `1`

otherwise it is `0`

(`1`

here means that `$int`

is an Odd number, so we have to inverse `1`

and cast it to `bool`

to make the function return `false`

in such case). The outcome is reversed using `!`

(Not) operator. `!`

operator reverts its operand i.e the answer of the whole expression, and casts the result to `bool`

.

Another alternative is using bitwise `^`

(Xor) operator that can replace `!`

logical Operator.

1 2 3 | function is_even( $int ) { return ( ( ( int ) $int ) & 1 ) ^ 1; } |

More variants that use bitwise operators:

1 2 3 | function is_even( $int ) { return !( ( ( ( int ) $int ) << 31 ) >> 31 ); } //See Note |

and also…

1 2 3 | function is_even( $int ) { return ( ( ( ( int ) $int ) << 31 ) >> 31 ) ^ 1; } //See Note |

**Note**: Above two functions that use `<<`

and `>>`

bit shifting operators that do not work with negative integers, so use with caution. In the presence of better alternatives, these are listed here just for your information.

More variants are possible using bitwise operators but I stick it to above functions.

The simplest and the most obvious solution to finding even and odd numbers is using `%`

operator.

1 2 3 | function is_even( $int ) { return !( ( (int) $int ) % 2 ); } |

It divides the `$int`

by `2`

and checks the remainder. If the remainder is `1`

means the number is Odd, `!`

operator reverts return value to `false`

, otherwise it returns

`true`

.

Now, how to use these functions:

1 2 3 4 5 6 7 8 9 | $number = 3432; if( is_even( $number ) ) { echo 'This is even.'; } if( !is_even( $number ) ) { echo 'Not an Even.'; } |

### Performance

All of these functions work equally fine and have the same performance with less than 5% variance.