Validating radio buttons in php

If you're getting an undefined error on the HTML page, just can add an isset() check to the logic where you're printing out the value. E.g.:

<input type="radio" name="degree_type" value="JD" <?php if (($_POST['degree_type']) == 'JD') {echo 'checked="checked"';} ?> >JD

Becomes

<input type="radio" name="degree_type" value="JD" <?php if (isset($_POST['degree_type']) && $_POST['degree_type'] == 'JD') {echo 'checked="checked"';} ?>>JD

An 'undefined index' error in PHP means that you are using an undefined variable in an expression. So for example, when you did:

<?php if (($_POST['degree_type']) == 'MA') {echo 'checked="checked"';} ?>

$_POST['degree_type'] was undefined. There's a couple of different possible reasons why the variables are undefined. I'd have to see the rest of the PHP file to know the exact cause.

One reason could be that the form was not properly submitted. Another reason could be that the expression was evaluated before the form was submitted.

Either way, the code below should work. Note that I'm checking if each field is set before attempting to validate it or compare it's value.

NOTE: Obviously you have to have a proper HTML doctype, opening and closing body tags etc. The HTML in this example is only the form portion of the page.

 <!-- myform.php -->
    <form name="my-form" method="POST" action="/myform.php">

        <span>What degree do you have?</span>
        <label for="bs">BS</label>
        <input type="radio" name="degree" id="bs" value="BS" <?php if(isset($degree) && $degree == 'BS') echo 'checked="checked"';?> />

        <label for="ma">MA</label>
        <input type="radio" name="degree" id="ma" value="MA" <?php if(isset($degree) && $degree == 'MA') echo 'checked="checked"';?> />

        <label for="phd">PHD</label>
        <input type="radio" name="degree" id="phd" value="PHD" <?php if(isset($degree) && $degree == 'PHD') echo 'checked="checked"';?> />


        <span>Which do you like better?</span>
        <label for="steak">steak</label>
        <input type="radio" name="food" id="steak" value="steak" <?php if(isset($food) && $food == 'steak') echo 'checked="checked"';?> />

        <label for="lobster">lobster</label>
        <input type="radio" name="food" id="lobster" value="lobster" <?php if(isset($food) && $food == 'lobster') echo 'checked="checked"';?> />

        <input type="hidden" name="submitted" value="submitted" />
        <input type="submit" name="submit" value="submit" />

    </form>

    <?php
    if (isset($_POST['submitted'])) {

        $errors = array();

        if (isset($_POST['degree'])) {
            $degree = $_POST['degree'];
        } else {
            $errors[] = 'Please select your degree type.';
        }

        if (isset($_POST['food'])) {
            $food = $_POST['food'];
        } else {
            $errors[] = 'Please select your food preference.';
        }

        if (count($errors) > 0) {
            foreach($errors as $error) {
                echo $error;
            }
        } else {
            echo 'Thank you for your submission.';
        }
    }
    ?>

The reason you see these notices is because $_POST['degree_type'] is simply not set. Either by typo, or it just didn't get submitted (because you didn't select any before submitting the form).

Also note,

if ($_POST['degree_type'] == "MS"||"MA"||"MBA"||"JD"||"PhD") {

It doesn't work that way. This will check that $_POST['degree_type'] == "MS" OR: "MS" is truthy (always true) OR "MA" is truthy (always true)... see where I'm heading?

if (in_array($_POST['degree_type'], array("MS", "MA", "MBA", "JS", "PhD")) {

Is a better alternative.

Unrelated:

You should really use <label> elements to markup your labels. Example:

<label><input type="radio" name="degree_type" value="MA"> MA</label>.

This will have MA clickable.

When a form is submitted with no member of a radio button group (defined as the group of radio buttons whose name attributes are the same) selected, the submitted data doesn't include that name at all.

This is why you're getting the "undefined index" error (actually a notice); when you test the value of $_POST['degree_type'], and no radio button named "degree_type" was selected, $_POST['degree_type'] doesn't exist at all.

Fortunately, this simplifies your validation task. By calling array_key_exists('degree_type', $_POST), you can find out whether or not the key is present, and thus whether or not a radio button was selected, without prompting the PHP "undefined index" notice. If the function call returns true, you know that a radio button was selected; otherwise, you know one wasn't, and that's what your validation is trying to determine. Therefore:

if (array_key_exists('degree_type', $_POST)) {
  $degree_type = $_POST['degree_type'];
}
else {
  array_push($errors, "Please select a degree type.");
};

will cleanly accomplish your task.

//set a default 
$degree_type = "";
if (isset($_POST['degree_type'])) {
    $degree_type = $_POST['degree_type']; 
} else {
    $errors[] = 'Please select a degree type.';
}

Then instead of using

if (($_POST['degree_type']) == 'MA') 

for your checks, use:

if($degree_type == 'MA')

undefined index means that the key you are using hasn't been initialized. So $_POST['degree_type'] won't appear until after the first time the form is submitted.