Trouble with arrays

[ShawnD]

I'm trying to make a script which can find all the factors of a number.

<?php
if (isset($HTTP_POST_VARS['number']))
{
	$n = intval($HTTP_POST_VARS['number']);
	if ($n > 1)
	{
		$a = 1;
		$array_num = 0;
		while ($n > $a) 
		{
			if (($n - ($n % $a) * $a) == 0)
			{
				$factors_array['$array_num'] = $a;
				$array_num = $array_num + 1;
			}
			$a = $a + 1;
		}
	foreach($factors_array as $factor)
	{
		echo "$factor\n";
	}
	}
	else
	{
		echo "the number entered is not an integer greater than 1";
	}
}
?>

The error I get is "PHP Warning: Invalid argument supplied for foreach() in \factors.php on line 34"

The foreach() function looks pretty good. I think the problem is where I'm trying to assign $factors_array['$array_num'] to $a.

I don't even have a clue what I should change. Any suggestions at all?

[drew010]

replace $array_num = 0; with $factors_array = array();

you dont need to manually keep track of the last used array index like c++. you can automatically push a value to the end of an array like this:
$factors_array[] = $a;

new code:

<?php
if (isset($HTTP_POST_VARS['number']))
{
	$n = intval($HTTP_POST_VARS['number']);
	if ($n > 1)
	{
		$a = 1;
		$factors_array = array();
		while ($n > $a) 
		{
			if (($n - ($n % $a) * $a) == 0)
			{
				$factors_array[] = $a;
			}
			$a = $a + 1;
		}
	foreach($factors_array as $factor)
	{
		echo "$factor\n";
	}
	}
	else
	{
		echo "the number entered is not an integer greater than 1";
	}
}
?>

[rpanning]

You are correct. Replace

$factors_array['$array_num'] = $a;
$array_num = $array_num + 1;

With

$factors_array[$array_num] = $a;
$array_num++;

You just needed to remove the quotes in the array index. Because they were single qutoes PHP didn't get the variable, it just set the index to the string '$array_num'. I've also shortened your addition.

[ShawnD]

I tried rpanning's advice, and it yeilded the same error.
I tried drew010's advice and the error went away, but the script still doesn't work :p.

[drew010]

here's something i just made and tested. seems to work fine.

<?php

$n = 100;
$factors = array();

if ($n > 1) {
	for($a = 1; $a <= ($n / 2); $a++) {
		if ($n % $a == 0) {
			$factors[] = $a;
		}
	}

foreach($factors as $factor) {
	echo "$factor<br />\n";
}
} else {
	echo "The number is not an integer greater than 1.";
}

?>

output was:
1
2
4
5
10
20
25
50

i start the for loop at 1, and loop until half of n, because there are no factors of n greater than 0.5n (except for itself of course, and if you use decimals you could factor it). use modulus very simply to see if there is no remainder when dividing by a, if there is none, its a factor and push it to the array, otherwise keep looping. you may want to add for checking is make sure the user entered an integer and not a decimal.

[ShawnD]

Oh snap, I was confusing div (it's a function in Pascal) with modulus. I forgot that modulus is the remainder, and div is how many times it divides. I replaced this:
($n - ($n % $a) * $a) == 0
with this:
$n % $a == 0

Now the script works great.
Thanks for helping me fix these problems 🙂.

I really like that part you added where it only counts up to half. That's a really nice optimization I would never think of.