Need to create a number with 4 letters all the time

loureiro

hi, i was wondering if there was a way to randomly generate a number with 4 digits no matter what.

ie. 0003, 0234, 6589

batman

Try this:

function makeRandomPassword() {
  $salt = "0123456789";
  srand((double)microtime()*1000000); 
  	$i = 0;
  	while ($i <= 7) {
    		$num = rand() % 33;
    		$tmp = substr($salt, $num, 1);
    		$pass = $pass . $tmp;
    		$i++;
  	}
  	return $pass;
}

$pass = makeRandomPassword();

I'm not sure what you are to change to get it to produce only 4 digits. As of right now it produces 8 digits.

mark_and_co

I assume changing the line

while ($i <= 7) {

with

while ($i <= 3) {

will make it 4 digits

batman

Most likely. But I wasn't sure about this line:

srand((double)microtime()*1000000);

The 1000000 adds up to seven as well. So if what you said is changed, would we have to change 1000000 to 100??

I don't believe so though, I think that if we just change the line you said, we should be fine.

zeb

Here is an easier approach - I like to use, mt_rand() which is arguably better than rand()

mt_srand((double)microtime()*1000000);
$randomNumber = mt_rand(0,9999);

When you call the mt_rand() function (or the rand() function), you can specify a lower and upper limit to the number it will produce.
When you output the number, you need to use printf() to preserve the number of digits when the random number is less than 1000.

mt_srand((double)microtime()*1000000);
$randomNumber = mt_rand(0,9999);
// add this line for output
printf("%04s", $randomNumber);

The first argument in the printf() function "%04s" is the formatting string. The modulus character '%' indicates the start of the format. The '0' indicates that we want the extra space padded with the number '0'. The '4' indicates that we want the length to always be at least 4 digits. And the 's' indicates that we want to print the variable (from the second argument) as a string.

The printf() function doesn't actually alter the $randomNumber. So if you need to store a 'zero-padded' 4-digit number (or do other things with this number which require it to be 'zero-padded'), you could change the function to create a number one digit at a time and join them with the concatenation operator (the period), which will treat the $randomNumber as a string and thus not truncate the leading zeros: (this is how batman's function is set up)

mt_srand((double)microtime()*1000000);
$randomNumber = '';
$i = 0;
while ($i < 4)
	{$randomNumber .= mt_rand(0,9);
	$i++;}
echo $randomNumber;

Give that a shot.

zeb

Batman, I just thought I would let you know about a few bugs in your function. If you want to pick a random character from your '$salt' string, then you need to know the length of the string so you don't try to choose a sub-string beyond the string length. There is no need for the "rand() % 33;" line. Try making the following changes:

function makeRandomPassword() {
	$salt = "0123456789";
	srand((double)microtime()*1000000); 
	$i = 0;
	while ($i <= 4) { // this is the number of digits
		$length = strlen($salt);
		$num = rand(0, $length - 1);
		$tmp = substr($salt, $num, 1);
		$pass = $pass . $tmp;
		$i++;
		}
	return $pass;
	}

$pass = makeRandomPassword();

with this method, you don't need to 'pad' the string out if it starts with a '0' (like my first example) because by using the concatenation operator (the period), you are implicitly saying "treat the $pass as a string". Your function is also better equipped to take on the function of producing a string of any character and length because you can simply change the $salt string to contain letters and symbols, and you can change the length of the output by setting the $i variable accordingly.

My method in the last post is just for numbers.

batman

The way I use it above is just fine for me. I mainly use something like mine over yours, because it produces numbers and letters in the way I use it. It should work just how it stands.

zeb

I hope I didn't offend you. It's just that when I run your function as it was posted, I tend to get $pass with only one or two characters half the time. I believe this is due to the "rand() % 33;" line which is returning a value between 0 and 32. Since the $salt string is only 10 characters long, the substr() is attempting to get a substring of the $salt string at a position after the end of the string, which will cause it to return false (which happens 10/32 times - a third of the time). I very rarely got a string that was more than 4 characters long. To see what I mean, try this variation of your function:

srand((double)microtime()*1000000);
$salt = "0123456789";
$i = 0;
while ($i <= 7) {
	$num = rand() % 33;
	echo "num is: $num<br>";
	$tmp = substr($salt, $num, 1);
	echo "tmp is: $tmp<br>";
	$pass = $pass . $tmp;
	$i++;}
echo "pass is: $pass<br>";

You'll see that the $tmp variable isn't defined about a third of the time, and that the $num variable is greater than 10 most of the time.

You could replace the '33' in your script with a '10' to correct this.

HalfaBee

Isn't the answer to the original questyion this.

( srand is not needed since php 4.2.0 )

sprintf( "%04d",rand( 0,9999 ) );

Halfabee

batman

Zeb - I know what you mean. I just remembered that it gives out random numbers, at multiple lenghts. When I got the code, I was setting it up to just give out any old combination of numbers and letters, not to give me a set length of just numbers. This code can work for him, with a few modifications. 🙂

zeb

Batman - Ten Four. 🙂

HalfaBee - cool. I hadn't realized that seeding was no longer neccessary.