for loops trying to understand

jesushax · March 28, 2008

hi im looking at this code and im trying to udnerstand it

i know it prints hello world 5 times but

and it goes (initialization, conidtion,increment) but i really need someone to dumb it down for me if they could

i undersatnd the conidtion thats imple maths but the initilaiztion and the increment how do they work and sutff?

Cheers

<html>
<body><?php
for ($i=1; $i<=5; $i++)
{
  echo "Hello World!<br />";
}
?></body>
</html>

ysamu · March 28, 2008

for (start with $i equals 1; do what is between curled brackets while $i is lesser or equals to 5; after doing what is in the barckets add 1 to $i )

{

echo "Hello World!<br />";

}

wildteen88 · March 28, 2008

for (start with $i equals 1; do what is between curled brackets while $i is lesser or equals to 5; after doing what is in the barckets add 1 to $i )

{

echo "Hello World!<br />";

}

That is incorrect.

for(  $i = 0   ;                                         $i <= 5                         ;                      $i++                      )
for(set $i to 1; if the condition is true (in your case if $i is less than or equal to 5); then increment $i and execute code in the braces)

discomatt · March 28, 2008

Here's another example of what it's doing, in pure code:

<?php

$i = 0;

while ( $i <=5 ) {
  echo 'Hello world<br>';
  $i = $i + 1;
}

?>

Cep · March 28, 2008

Ok I'll give you a breakdown.

For loops are controlled by the 3 expressions you see.

$i = 1; // first expression

$i<=5; // second expression

$i++; // third expression

First your saying that the control variable $i will start at the value 1.

It could start at any value you like, in fact it could be any variable you like too such as $x or $zebidee as long as its value is one you can control with the other two expressions.

This as you guessed is the initialisation expression.

The second expression, $i <= 5; means that the loop must only loop if the value of $i is less than or equal to 5.

This condition expression can also be different to what we see here, it could be $i < 2; which would cause our current loop to loop only once because $i = 1, and therefore $i must be less then 2, (1 or 0) so loop once.

The third and final part basically says, take the value of $i and now add 1 to it. Or $i = $i + 1;

The loop will then fire and go back to the condition statement. It will ignore the initialisation statement because $i already exists.

$i is now 2 because we incremented it on that previous loop using $i++; It will then re-evaluate the value against the condition so is 2 less than or equal to 5? The answer is yes, so move onto the increment statement $i++ ($i = $i + 1 or 3 = 2 + 1)

The loop will fire again and keep re-evaluating until finally the condition fails (when $i is no longer less than or equal to 5, when it becomes 6) at which point it will exit the loop.

jesushax · March 28, 2008

ok thanks, i think of got it now but i still cant figure this out...

what the below does it print each 'PortTitle' 3 times and move to the next row and do the same for all the other records

i want the rows to increment after portitle has been displayed in a row 3 times

so

title 1 | title 2 | title 3

title 4 | title 5 | title 6

title 7 | title 8 |

<?php

include($_SERVER['DOCUMENT_ROOT'] . '/includes/connection.php');

$res = mysql_query("SELECT * FROM tblPortfolio WHERE PortType='Web' ORDER BY PortDateAdded DESC") or die(mysql_error());
$data="";

$data .="<table><tr>"."\n";
while($row=mysql_fetch_array($res))  {

for ($i=1; $i<=3; $i++){
$data .="<td>". $row['PortTitle']."</td>"."\n";
}      

$data .="</tr><tr>"."\n";   
}
$data .="</tr></table>"."\n";   
echo $data;
?>

discomatt · March 28, 2008

Before we can really help, you, please execute this code and paste the output so we can see the kinda data you're working with:

<?php

while($row=mysql_fetch_array($res))  {

$a[] = $row;

}

echo '<pre>';
print_r($a);
echo '</pre>';

?>

jesushax · March 28, 2008

that code gave this...

discomatt · March 28, 2008

Okay, so my assumption is you just want to list portTitle's out in a 3 column layout?

Try this code:

<?php

include($_SERVER['DOCUMENT_ROOT'] . '/includes/connection.php');

// Restrict our query to only the data we want. No sense in wasting memory on stuff we dont need
// Also goo pratcise to backtick (`) all mysql tables and columns
$res = mysql_query("SELECT `portTitle` FROM `tblPortfolio` WHERE `PortType`='Web' ORDER BY `PortDateAdded` DESC") or die(mysql_error());

// Set a new variable that keeps track of the current column.
$col = 1;
// Set a new vairable defining how many columns we want
$colMax = 3;

// Start the table
echo "<table border=\"1\">\n";
// mysql_fetch_assoc only returns an associative array, rather than both numeric and associative.
// this is to save a bit of memory as well
while($row=mysql_fetch_array($res))  {

// check if this is the first column
 if ($col == 1)
	// if it is the first row, echo the html
	echo " <tr>\n";

// Echo the data as usual
echo "  <td>$row['portTitle']</td>\n";

// Check to see if the row is equal to $colMax (meaning this is the last column)
if ($col == $colMax) {
	// If it is, echo the ending html and reset $col to start over
	echo " </tr>\n";
	$col = 1;
// Otherwise, increment $col and move on to the next entry
} else
	$col++;

}

// Now here's the trick. Imagine you have 8 results.
// 8/3 doesn't go well, you'll be left with a blank
// column that won't be echo'ed. We dont want that.
// But thankfully we've tracked our current column,
// and can filll the rest with blank cells

// Loop until $col > $colMax, but not if $col = 1 (in the
// above loop, $col is set to 1 after a </tr> is echo'ed,
// so it would mean clean results). Also, in the above loop
// if we ended on the second column, $col would iterate at
// the end with a value of 3 even though we are left with an
// empty cell... this is why we use <=
while ($col <= $colMax && $col !== 1) {

// Echo blank cell
echo "  <td> </td>\n";
// Increment column by 1.. if this is that last one, it will
// define it as $colMax + 1
$col++;

// Once again, check if this is the last column. 
if ($col > $colMax)
	// If it is, echo the ending html
	echo " </tr>\n";

}

// Finally, echo the closing table
echo "</table>\n";
?>

I usually don't like to code for people, but you show an honest attempt to learn and understand. If there's anyting in this script you don't understand, letm e know and i'll explain further.

Oh and you can replace the echo's with $data .= and it will work just as you had it before.

jesushax · March 28, 2008

bloody marvellous

thanks friend

also thast alot for the desctiptions helps alot!

keeping that stored for future ref

thankyou! :D

discomatt · March 28, 2008

Boy am i silly... replace

while($row=mysql_fetch_array($res))

with

while($row=mysql_fetch_assoc($res))

------------------------

or alternately, you could use

while($row=mysql_fetch_row($res))

and then you would call $row[0] instead of $row['portTitle']. This save a tiny bit of memory, but I usually don't use it, as it is a little less convenient, especially using SELECT * where you don't define the order of the rows.

------------------------

Glad I could help though. Everyone's a beginner at some point. I'm just glad you actually asked for guidance and not 'heres the code find the error, tell me where to put it'

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