Why isn't my nested while loop generating desired output?

Question

Last question wasn't received well so I've done more reading and came up with a simple php program that accepts user input for number of rows and columns. A table is generated using nested while loop and I do understand that a 'For' loop is more suited for this and got it working using one. Trying to learn and get better so I want to figure this one out too. I'm getting one row only and no columns. I also want the iteration to produce rows and columns that appear like the example. Kind of frustrated the for loop was much easier to finally figure out.

W,row1,col1; W,row1,col2; W,row1,col3
W,row2,col1; W,row2,col2; W,row2,col3 etc...

php code:

<?php

if(isset($_GET['rows'])) { 



$r = 1;
$c = 1;
$rows = 5;
$cols = 6;
while ($r <= $rows) {
        echo '<tr>';
        while($c <= $cols) {
            echo '<td>W, '.'row' .$r.',col'.$c.';</td>';
            $c++;
        }
        echo '</tr>';
        $r++;
    }   

    ?>

you have nothing keeping track of how many loop iterations you have done. Think about what the code is doing and sound it out in words. $rows is always the same number, you need to have something that decrements $rows (and $cols of course) on each iteration of the loop so that eventually it will no longer be >=1. You are also missing a semi-colon on $count++. I hope this helps. — James McCormac
– James McCormac, Commented Apr 12, 2016 at 20:47
thanks, I'm going to change the evaluation condition to ($rows != 0) and cols the same. And of course keep a counter for rows....thanks! — allendks45
– allendks45, Commented Apr 12, 2016 at 21:18

Barmar · Accepted Answer · 2016-04-12 21:34:51Z

1

You're never changing the variables that you're testing in the while conditions, so the loops are infinite. You need to decrement the variables each time.

And you need to re-initialize $cols before each inner loop. Otherwise, the end condition will already be met after the first iteration of the outer loop.

$count = 1;
$rows = $_REQUEST['rows'];

//while loop to create table

while ($rows-- >= 1) {
    echo '<tr>';
    $cols = $_REQUEST['cols'];
    while ($cols-- >= 1) {
        echo '<td>W,row1,col1;</td>';
        $count++
    }
    echo '</tr>';   
}

answered Apr 12, 2016 at 21:34

Barmar

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Barmar · Accepted Answer · 2016-04-12 21:30:29Z

0

YOu can do it like this:

if(isset($_GET['rows'])) { 

//Create counters

    $count = 1;
    $rows = $_REQUEST['rows'];
    $cols = $_REQUEST['cols'];

    //for loop to create table

    for($i=1;$i<=$rows;$i++){
        echo '<tr>';
        for($j=1;$j<=$cols;$j++){
            echo '<td>W,'.'row'.$i.',col'.$j.';</td>';        
        }
        echo '</tr>';
    }
}

edited Apr 12, 2016 at 21:30

Barmar

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answered Apr 12, 2016 at 20:53

Aparna

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1 Comment

allendks45 Over a year ago

I got it working with the for loop above with the output formatted correctly. Will make changes to the while loop. Been staring at this for nearly 3 hours and missed the semi colon and should have used the ($rows != 0). I'm sure with the comments here I'll figure it out. Never hurts to get another set of eyes on it.

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