javascript - Radio button automatic change the data in php -

i new php keeping 2 radio buttons 1 checked default when page loaded content should displayed radiobutton based content default

i think understand,

   <?php    $sex='male';    ?>   <input type="radio" name="sex" value="male"  <?php if($sex=='male') echo 'checked="checked"'; ?>>male<br>   <input type="radio" name="sex" value="female" <?php if($sex=='female') echo 'checked="checked"'; ?>>female 

output