## PHP Prime Number Script

Here is a simple little script that will determine if a number is prime or not. Just submit the function through with the parameter *number* as the integer you want to determine – is prime or not.

# Syntax

is_prime(number);

Here is the function’s definition:

function is_prime($num=0) { $num = (int)$num; // Make sure it's an integer. if($num > 0) { $count = 0; $half = round($num / 2); for($i=2;$i<=$half;$i++) // Check the remainder from 2 to the half point. { if(($num % $i) == 0) // Remainder is 0, it is divisible. Not a prime number. { $count++; // Increase count of divisible numbers. } } if($count > 0) { return false; } else { return true; } } else { return false; } }

Examples:

is_prime(10); is_prime(3); is_prime(109);

false true true

Basically our script here takes a parameter, makes sure it is an integer greaterĀ than 0, then divides it by each number from 2 to half way to that number. So if our number was 7 the script would divide 7 by 2, 3, 4. The half mark is rounded to the nearest whole number. Since a remainder exists from each of these divisions, the number is declared as prime.