How to multiply elements of php array

Question

I'm trying to translate a javascript function into php but having some problems with my arrays. I need to iterate over the array elements, multiplying them all by a certain amount, but it's not changing the values. Pretty sure it's because my syntax $coordinates_p[i][0] *= $scale; isn't correct, but I'm not sure what it should be!

Test code:

<?php

print "Starting.<br/>";

$scale = 100;

$coordinates_p = array();

$i = 0;
$x_coordinate = 1;
$y_coordinate = 2;
while ($i <= 1) {
    $coordinates_p[$i] = array(0 => $x_coordinate, 1 => $y_coordinate);
    $x_coordinate += 1;
    $y_coordinate += 2;
    $i++;
}

print "Unscaled: ";
print_r ($coordinates_p);
print "<br/>";

$i = 0;
while (isset($coordinates_p[i])) {
    $coordinates_p[i][0] *= $scale;
    $coordinates_p[i][1] *= $scale;
    $i++;
}

print "Scaled: ";
print_r ($coordinates_p);
print "<br/>";

print "Finished.";

?>

Paul Kehrer · Accepted Answer · 2010-11-17 19:39:18Z

6

Your code just needs to change from

$coordinates_p[i][0] *= $scale;
$coordinates_p[i][1] *= $scale;

to

$coordinates_p[$i][0] *= $scale;
$coordinates_p[$i][1] *= $scale;

answered Nov 17, 2010 at 19:39

Paul Kehrer

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3 Comments

Mike Over a year ago

Keep on missing those! But unfortunately it still doesn't work.

Gordon Over a year ago

@Mike then you also missed the one in the isset above those two. Always enable error_reporting(-1) on development servers and make sure you set your display_errors directive in php.ini and PHP will tell you about these things.

Mike Over a year ago

My bad, there was another one I'd missed. Working fine now!

Shadow Radiance · Accepted Answer · 2010-11-17 19:48:55Z

1

Your error is in

while (isset($coordinates_p[i])) {
    $coordinates_p[i][0] *= $scale;
    $coordinates_p[i][1] *= $scale;
    $i++;
}

it should use $i not i.

like so:

while (isset($coordinates_p[$i])) {
    $coordinates_p[$i][0] *= $scale;
    $coordinates_p[$i][1] *= $scale;
    $i++;
}

answered Nov 17, 2010 at 19:48

Shadow Radiance

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2 Comments

Mike Over a year ago

Yes, thanks. That will teach me to cut and paste from javascript!

Shadow Radiance Over a year ago

jon_darkstar's answer here is also a good note - I was just fixing your code. Using the foreach approach would be "better" php. Even a for loop (bounded) would be a better approach than a potentially infinite while loop.

Community · Accepted Answer · 2020-06-20 09:12:55Z

1

Depends on how "deeply" you want to translate

Shallow - put a $ in front of every variable

Deeper - put $ in front of variables, change those while loops to foreach, change print to echo

//before
$i = 0;
while (isset($coordinates_p[i])) {
    $coordinates_p[i][0] *= $scale;
    $coordinates_p[i][1] *= $scale;
    $i++;
}

//Better PHP form
foreach($coordinates_p as $current)
{
   $current[0] *= $scale;
   $current[1] *= $scale;
}

They'll each run, but you're not really USING php if you do those while loops. For a more extreme example, post code with lots of while loops up with a "python" tag and ask if it can be simplified.

foreach loops and echo are idiomatic php, while loops and print only works.

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Nov 17, 2010 at 19:56

jon_darkstar

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1 Comment

Mike Over a year ago

Ok, thanks. Never really learnt any programming language properly, just dabble around and try and get the end result I need. Would probably be worth investing some time in it though, I seem to be doing more and more recently. Thanks for the tip!

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