Step-by-step explanation:

Note that when you use implementation of factorial that CLAUDIUS made, you get RESULTS even if you try to calculate factorial of number that you normally can't, e.g. 2.5, -2, etc. Here is safer implementation:

/**

* Calculates a factorial of given number.

* @param string|int $num

* @throws InvalidArgumentException

* @return string

*/

function bcfact($num)

{

if (!filter_var($num, FILTER_VALIDATE_INT) || $num <= 0) {

throw new InvalidArgumentException(sprintf('Argument must be natural number, "%s" given.', $num));

}

for ($result = '1'; $num > 0; $num--) {

$result = bcmul($result, $num);

}

return $result;

}

?>

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15ClaudiuS ¶7 years ago

Needed to compute some permutations and found the BC extension great but poor on functions, so UNTILL this gets implemented here's the factorial function:

/* BC FACTORIAL

* n! = n * (n-1) * (n-2) .. 1 [eg. 5! = 5 * 4 * 3 * 2 * 1 = 120]

*/

function bcfact($n){

$factorial=$n;

while (--$n>1) $factorial=bcmul($factorial,$n);

return $factorial;

}

print bcfact(50);

//30414093201713378043612608166064768844377641568960512000000000000

?>

HOPE it is helpful to u ...