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
[code lang=”php”]
is_prime(number);
[/code]
Here is the function’s definition:
[code lang=”php”]
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;
}
}
[/code]
Examples:
[code]
is_prime(10);
is_prime(3);
is_prime(109);
[/code]
[code]
false
true
true
[/code]
Basically our script here takes a parameter, makes sure it is an integer greater 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.