[RESOLVED] Can't wrap thick head around while() loop

[bunner_bob]

I need help writing a looping function. I'm sure it's simple but I can't wrap my head around it.

I want to generate a random number, check whether it's in a database table field, if it IS, then generate a new random number and check again, otherwise go ahead and insert it.

I started with:

$rand = substr(microtime(), -8); // give me 8-digit number

$query = 'SELECT Count(*) FROM Certification WHERE CertificateNumber=$rand';
$result = mysql_query($query);
if ($result == 0) { // insert record };

I think I need some kind of while() loop, but I can't figure out how to get the random number-maker inside the loop and yet have it before the loop - unless I put it in twice.

I know there's an elegant way to do this that those of you who actually use while loops more than me will know. I'd appreciate a nudge in the right direction.

Thanks!

• Bob

[bradgrafelman]

Actually, IF the CertificateNumber column is a key, you could probably just generate the random number within the MySQL query:

 INSERT INTO `Certification` (`name`, `CertificateNumber`) VALUES ('Name here', FLOOR(10000000 + RAND() * 89999999) ) ON DUPLICATE KEY UPDATE `CertificateNumber` = FLOOR(10000000 + RAND() * 89999999);

EDIT: Alternatively, to follow your method and do a SELECT each time to make sure:

for( $i=0, $max=50, $rand=mt_rand(10000000, 99999999); $i < $max; $i++,$rand=mt_rand(10000000, 99999999) ) {
     $query = 'SELECT TRUE FROM Certification WHERE `CertificateNumber`=' . $rand . ' LIMIT 1';
     $exec = mysql_query($query) or die('MySQL Error - ' . mysql_error());

 if(mysql_num_rows($exec) > 0) {
      if($i == $max)
           die('Error - could not generate an unused random number after 50 times, or the script is erraneous.');
      else
           continue;
 } else {
      $ins_query = 'INSERT INTO `Certification` (`name`, `CertificateNumber`) VALUES (\'Name here\', ' . $rand . ')';
      $ins_exec = mysql_query($query) or die('MySQL Error - ' . mysql_error());

      break;
 }
}

The above code is untested, but it looks like it should do what you need it to.

[peachP]

bunner bob wrote:

I need help writing a looping function. I'm sure it's simple but I can't wrap my head around it.

I want to generate a random number, check whether it's in a database table field, if it IS, then generate a new random number and check again, otherwise go ahead and insert it.

I started with:

$rand = substr(microtime(), -8); // give me 8-digit number

$query = 'SELECT Count(*) FROM Certification WHERE CertificateNumber=$rand';
$result = mysql_query($query);
if ($result == 0) { // insert record };

I think I need some kind of while() loop, but I can't figure out how to get the random number-maker inside the loop and yet have it before the loop - unless I put it in twice.

I know there's an elegant way to do this that those of you who actually use while loops more than me will know. I'd appreciate a nudge in the right direction.

Thanks!

• Bob

try this - i used similar logic in my own site:

while(1){
 $rand = substr(microtime(), -8); // give me 8-digit number 
 $query = 'SELECT Count(*) FROM Certification WHERE CertificateNumber=$rand'; 
 $result = mysql_query($query);
 if (!$result) { insert_record(); break;} else continue;
}

function  insert_record(){
 blah...blah...
}

[rbblue8]

peachP wrote:

try this - i used similar logic in my own site:

while(1){
 $rand = substr(microtime(), -8); // give me 8-digit number 
 $query = 'SELECT Count(*) FROM Certification WHERE CertificateNumber=$rand'; 
 $result = mysql_query($query);
 if (!$result) { insert_record(); break;} else continue;
}

function  insert_record(){
 blah...blah...
}

so i have a newb question for you..

i take it the code

while(1){ }

would make the while loop go once?
and i take it the code

break;

tells the while loop to stop?
and the code

contine;

tell the while loop to go again?

[m_tt]

Simple idea.... not tested.

$match = false;

while(!$match)	{

$id = rand();
$result = mysql_query("SELECT * FROM `table` WHERE `id` = '{$id}'");

if (mysql_num_rows($result) < 1)	{
	$match = true;
}

}

basically the same as peachP's example.

[peachP]

while(1) equates to while true - this will keep a loop going for ever.
Be warned: ONLY USE IT WHEN YOU HAVE SOME CONDITION INSIDE THE LOOP TO STOP IT OTHERWISE YOU'LL ENCOUNTER THE 'UNCONDITIONAL -LOOP' WHICH WILL REQUIRE A 'PAUSE-BREAK KEYBOARD KEY ESCAPE OR IF YOUR UNLUCKY A COMPLETE REBOOT!!

break;

- break keyword: breaks out of the loop and excecution begins at the first line after the while loop

continue;

- continue keyword: skips any further lines within the loop, returns to top of loop and re-evaluates the conditional expression in while()

[bunner_bob]

Thanks everyone - lots of good advice. I'm going to have to go back and fix what I did, which is...

The script checks whether there is ANY CertificateNumber entry in the table - if not, it generates a random one; if there is one already there, it finds the MAX and increments by 1 (essentially an auto-increment)

Not as sexy as randomizing each time, but the people getting the certificates don't know the difference.

However, something about the principle of it being random appeals to me, so I think I'll work some variation of one of these in.

I also appreciate the general education I got from this thread. I still find a few functions kind of like speaking a foreign language - one of those ones where the verb goes at the end. switch() statements particularly, and while() as well.

Thanks!

• Bob