Q:

PHP form checkbox and undefined index

I am getting an "Undefined index" error when submitting a form with an un-checked checkbox. Is there any other way besides running an "isset" or "empty" check on each individual posted value?
I have looked at this Question and am having trouble believing that this is the only solution. 
Below is some example code:
EDIT: please not that these are not the actual names of the tables columns; they are named uniquely (like "postAddress, displayPhone, student, etc.)
    

A:

You could write a function that checks whether a checkbox was checked:
function checkbox_value($name) {
    return (isset($_POST[$name]) ? 1 : 0);
}

Now call that function in your query like this:
$sql =  'UPDATE table SET '.
        'checkbox1 = '. checkbox_value('checkbox1') .','.
        'checkbox2 = '. checkbox_value('checkbox2') .','.
        'checkbox3 = '. checkbox_value('checkbox3') .','.
        'checkbox4 = '. checkbox_value('checkbox4') .','.
        'checkbox5 = '. checkbox_value('checkbox5') .','. "LIMIT 1";

A:

If you want a on/off checkbox you can write a hidden value before you write the checkbox.
<input type="hidden" name="checkbox1" value="no" />
<input type="checkbox" name="checkbox1" value="yes" />

This will always return a value, either no (default unless checkbox is checked by default) or yes.
You can validate input with the filter functions with FILTER_VALIDATE_BOOLEAN.
Its easier if you write a function for this, like formCheckbox($name), with options for values (value 'on' means checkbox is checked by default), attributes, etc.

