Return error when checkbox isn't checked PHP

[system]

So I have been working on some code and have gotten some help the last few days, but now I am stuck again. I am trying to have an error pop up (using echo) when a user does not select a check box.

I have a variable $value set to 0 which is changed when users select a service(s) and hit submit causing it to increase. Instead I am getting a huge list of errors that look bad and unprofessional.

Here are the last few lines of my php code in which I am trying to get an error to return if my variable
$value = 0. I must also mention I am new to php.

[php]if ($value = 0) {
echo “Please choose one service.”;
}

if(in_array(‘a’ or ‘b’ or ‘c’ or ‘d’ or ‘e’ or ‘f’ or ‘g’ or ‘h’ or ‘i’, $services)) { // see if b is in the array

echo “The quote for the following service(s): " . implode(’, ', $service_list) . " will be a total of $” . number_format($value) . “.”;
}
}
[/php]

[lothop]

[php]if(in_array(‘a’, ‘b’, ‘c’, ‘d’, ‘e’, ‘f’, ‘g’, ‘h’, ‘i’, $services)) {[/php]

Your not giving us much to work with

[Russ]

First of all, posting it with two different accounts isn’t going to make us respond any quicker.
Second, here is how it is done:
[php]

<?php if(isset($_POST['checkbox'])) { } else { echo ""; } [/php] Have this on the recieving end of the form.

[Strider64]

This might be a little cleaner way of doing the same thing, but the first way is probably better?
[php]if(!isset($_POST[‘checkbox’])) echo “”;[/php]

or you might want a default checkbox, that way you wouldn’t have to worry about it in the first place.
Example

<input type="checkbox" name="gender" value="female" checked>Female