PHP总是从HTML表单中获取特定值

I have a HTML form in a wordpress site that sends data to a database. One of the fields asks if a person is male or female using a radio button. How ever even if the persons presses the "Female" radio button they get set to male (Status M)

I've attached my code, the <?php if( get_theme_mod( 'petition_zip' ) === true ) : ?> is only a check in my wordpress theme to see if the field should be there. I first tried using only HTML but added some PHP later to try and remidy the problem, it did not so as far as I can tell the PHP attached is close to useless

<?php
    $male_status = 'unchecked'; 
    $female_status = 'unchecked'; 
    if (isset($_POST['submit'])) {
        $selected_radio = $_POST['zip'];
        if ($selected_radio == 'M') {

            $male_status = 'checked';

            }
            else if ($selected_radio == 'F') {

            $female_status = 'checked';

            }

    }
?>
            <?php if( get_theme_mod( 'petition_zip' ) === true ) : ?>
            <div class="form-group">

                <input type="radio" id="zip" name="zip" value="M" <?PHP print $male_status; ?>>
                <label for="M">Male</label>

                <input type="radio" id="zip" name="zip" value="F" <?PHP print $female_status; ?>>
                <label for="F">Female</label>   
                </div>

            <?php endif; ?>

I'm running queries on the database to confirm the status, everyone that signs up is put to status "M" (Male)

The error is possibly in your petition.sign.js file.

I would try to replace this line:

$zip = $( 'input[name="zip"]', this ).val();

with this

$zip = $('input[name=zip]:checked').val();

I managed to solve the issue by re-writing the PHP from scratch, how ever I do believe that my solution would not have worked without the input from @superhenke. I've attached the working PHP-code.

        <?php
        if (isset($_POST["submit"])) {
            $male_status = "unchecked";
            $female_status = "unchecked";
            $other_status = "unchecked";
            $selected_radio = $_POST["zip"];
            if ($selected_radio == "M") {

                $male_status = "checked";
            }
            elseif ($selected_radio == "F") {

                $female_status = "checked";

            }

            elseif ($selected_radio == "other") {

                $other_stauts = "checked";
            }
        }
        ?>

        <?php if( get_theme_mod( 'petition_zip' ) === true ) : ?>
            <p>Select your gender:</p>
            <div class="form-group">
                    <input type="radio" id="male" name="zip" value="M" >
                    <label for="male">Male</label>

                    <input type="radio" id="female" name="zip" value="F">
                    <label for="female">Female</label>
                    <input type="radio" id="other" name="zip" value="O">
                    <label for="female">Other</label>
                </div>

        <?php endif; ?>