Incrementing variable in php after action is processed? - php

Question

Aim of my Program:
On my index.php file, an image is displayed.
I want that, when i user clicks that image, a new image should be displayed.
And when he clicks the new image, another new image should appear.
What have i done till now ?
<?php
$mycolor = array("red.jpg", "green.jpg", "blue.jpg");
$i = 0;
$cc = $mycolor[$i++];
?>
<form method="post" action="index2.php">
<input type="image" src="<?php echo $cc; ?>">
</form>
I know what the error is. Whenever, the page is reloaded, the variable $i is initialized to ZERO. How, do i fix that. How can I retain the incremented value after the image is clicked ?
Also, I have no Javascript Knowledge. So, if possible explain me in terms of php.

Answer 1

You have different possibilities to remember $i. e.g:
$_GET: http://php.net/manual/en/reserved.variables.get.php
Cookies: http://php.net/manual/en/function.setcookie.php
Sessions: http://php.net/manual/en/features.sessions.php
There is also no necessity to use a form for this problem. Just wrap the image with a hyperlink and modify the url by incrementing the parameter (index.php?i=1, index.php?i=2, index.php?i=3 and so on).

Answer 2

<?php
$mycolor = array("red.jpg", "green.jpg", "blue.jpg");
if (isset($_POST['i'])) { // Check if the form has been posted
$i = (int)$_POST['i'] + 1; // if so add 1 to it - also (see (int)) protect against code injection
} else {
$i = 0; // Otherwise set it to 0
}
$cc = $mycolor[$i]; // Self explanatory
?>
<form method="post" action="<?php echo $_SERVER['PHP_SELF']; ?>">
<input type="image" src="<?php echo $cc; ?>">
<input type="hidden" name="i" value="<?php echo $i; ?>"> <!-- Here is where you set i for the post -->
</form>

Answer 3

You can either use sessions, cookies or a POST variable to keep track of the index, but some how you need to remember the last index so you can +1 it. Here's an example using another (hidden) post variable:
<?php
// list of possible colors
$mycolor = array('red.jpg', 'green.jpg', 'blue.jpg');
// if a previous index was supplied then use it and +1, otherwise
// start at 0.
$i = isset($_POST['i']) ? (int)$_POST['i'] + 1 : 0;
// reference the $mycolor using the index
// I used `% count($mycolor)` to avoid going beyond the array's
// capacity.
$cc = $mycolor[$i % count($mycolor)];
?>
<form method="POST" action="<?=$_SERVER['PHP_SELF'];?>">
<!-- Pass the current index back to the server on submit -->
<input type="hidden" name="id" value="<?=$i;?>" />
<!-- display current image -->
<input type="button" src="<?=$cc;?>" />
</form>