While loop is over my head

Dave · 08-30-2009, 05:36 PM

Hi,

The WHILE and FOREACH loops below are elementary, yet how they work keeps evading my mental grasp. Here is a UDF:

PHP Code:


			
$c_pettype = "horse" ;
 
 function getpets($c_pettype)
 {
 
  $q = "SELECT *
       FROM t_petdata
         WHERE pettype = '$c_pettype'" ;
          
 $result = mysql_query($q) or die ('bad query') ;

 $j = 1 ;

 [color="Red"]while($row = mysql_fetch_assoc($result))[/color]
 { 
     [color="Red"]foreach($row as $key => $value)[/color]
     {
         $array[$j][$key] = $value ;
     }
                
     return $array ;
 }
 
}

So, I get the arrays, and the general concept of looping, etc., but the concepts of "WHILE($row = ...)" and "FOREACH($row as...) are not clear to me. I mean, where does "$row" come from?

Is there a way to help me understand this on a simple level?

Thanks!

Dave

Village Idiot · 08-30-2009, 06:13 PM

As you know, while loops will execute as long as a condition is true. The first one says while you can assign $row from mysql_fetch_assoc it can continue. When an array reaches its end you will not be able to assign it, making the while loop end. Mysql_fetch_assoc returns an array, so you can apply foreach to $row.

The syntax of foreach is
foreach($arr as $key => $value)

So the following code represents the values.

PHP Code:


			
$arr["key1"]  = 7; //$key=key1 $value = 7
$arr["key2"] = 15; //$key=key2 $value = 15
$arr["ABC"] = 23; //$key=ABC $value = 23

Dave · 08-31-2009, 03:01 AM

Thanks, VI...

That helps...I'm still trying to get the full hang of this concept.

while($row = mysql_fetch_assoc($result))
{...

...means

1. The variable $row will be assigned the value(s) of the array of the first row of the results of the db query (assuming the query was successful).

2. Do everything within the WHILE loop. Drop the pointer to the second row in the db query results.

3. If there is another row in the db query results, then $row will take the second row's array value and repeat the WHILE loop.

4. And on and on, until the pointer is passed the last row of the db query resultset, at which point $row will not contain a value, and the WHILE loop exits.

Does that sound about right for the WHILE loop statement?

Thanks again,

Dave

RishikeshJha · 08-31-2009, 08:17 AM

Quote:

Originally Posted by Dave

Hi,

The WHILE and FOREACH loops below are elementary, yet how they work keeps evading my mental grasp. Here is a UDF:

PHP Code:


			
$c_pettype = "horse" ;
 
 function getpets($c_pettype)
 {
 
  $q = "SELECT *
       FROM t_petdata
         WHERE pettype = '$c_pettype'" ;
          
 $result = mysql_query($q) or die ('bad query') ;

 $j = 1 ;

 [color="Red"]while($row = mysql_fetch_assoc($result))[/color]
 { 
     [color="Red"]foreach($row as $key => $value)[/color]
     {
         $array[$j][$key] = $value ;
     }
                
     return $array ;
 }
 
}

So, I get the arrays, and the general concept of looping, etc., but the concepts of "WHILE($row = ...)" and "FOREACH($row as...) are not clear to me. I mean, where does "$row" come from?

Is there a way to help me understand this on a simple level?

Thanks!

Dave

$row contains the value that is assigned mysql_fetch_assoc($result).

Village Idiot · 08-31-2009, 01:55 PM

Quote:

Originally Posted by Dave

Thanks, VI...

That helps...I'm still trying to get the full hang of this concept.

while($row = mysql_fetch_assoc($result))
{...

...means

1. The variable $row will be assigned the value(s) of the array of the first row of the results of the db query (assuming the query was successful).

2. Do everything within the WHILE loop. Drop the pointer to the second row in the db query results.

3. If there is another row in the db query results, then $row will take the second row's array value and repeat the WHILE loop.

4. And on and on, until the pointer is passed the last row of the db query resultset, at which point $row will not contain a value, and the WHILE loop exits.

Does that sound about right for the WHILE loop statement?

Thanks again,

Dave

1 and 2. Mysql_fetch_assoc returns a single row returned from the query as an array. It can keep track of itself and keep submitting the next row every time its called.

3. Yes, but not in your script since it returns before the loop can repeat.

4. Almost, I believe that the results are passed by value. But other that that, you are correct.

codefreek · 09-01-2009, 05:31 PM

ModNote: Please read this, and follow the right use of code tags,
Thank you,
Prettifying Pasted Code on TalkPHP
-CF

Dave · 09-02-2009, 02:31 AM

Thanks, VI and RishikeshJha --

After still spending a lot of time on this, I think I'm finally beginning to "get it" with these concepts.

It is always the same: frustrating at first, then later you look back and wonder what the fuss was all about...

I'm sure I'll have more questions a little later.

Dave