PHP checkbox input

http://www.html-form-guide.com/php-form/php-form-checkbox.html

This covers checkboxes, and checkbox groups.

Try this

<form action="form.php" method="post">
    Do you like stackoverflow?
    <input type="checkbox" name="like" value="Yes" />
 <input type="submit" name="formSubmit" value="Submit" />
</form>
<?php
    if(isset($_POST['like'])
    {
        echo "You like Stackoverflow.";
    }
    else
    {
        echo "You don't like Stackoverflow.";
    }   
?>

Or this

<?php
    if(isset($_POST['like']) && 
    $_POST['like'] == 'Yes') 
    {
        echo "You like Stackoverflow.";
    }
    else
    {
        echo "You don't like Stackoverflow.";
    }   
?>

you can check that by either isset() or empty() (its check explicit isset) weather check box is checked or not

for example

  <input type='checkbox' name='Mary' value='2' id='checkbox' />

here you can check by

if (isset($_POST['Mary'])) {
    echo "checked!";
}

or

if (!empty($_POST['Mary'])) {
    echo "checked!";
}

the above will check only one if you want to do for many than you can make an array instead writing separate for all checkbox try like

<input type="checkbox" name="formDoor[]" value="A" />Acorn Building<br />
<input type="checkbox" name="formDoor[]" value="B" />Brown Hall<br />
<input type="checkbox" name="formDoor[]" value="C" />Carnegie Complex<br />

php

  $aDoor = $_POST['formDoor'];
  if(empty($aDoor))
  {
    echo("You didn't select any buildings.");
  }
  else
  {
    $N = count($aDoor);
    echo("You selected $N door(s): ");
    for($i=0; $i < $N; $i++)
    {
      echo($aDoor[$i] . " ");
    }
  }

I did a blog post on determining if a checkbox is checked or not, in the case you want the value from either case to be in your $_POST array.

Check out http://www.martinbean.co.uk/web-development/the-check-box-input-element/ for a more in-depth explanation.