PHP User Registration Form

form.php

<div class="container" style="width:500px;background:#E6EFCB;">
  <?php if(!empty($error)):?>
  <div class="alert alert-danger">
    <?php foreach($error as $value):?>
    <?php print $value?><br>
    <?php endforeach;?>
  </div>
  <?php endif;?>
  <?php if(isset($_GET['msg'])&& $_GET['msg']==1):?>
  <div class="alert alert-success"> <strong>Success!</strong> Regsitered successfully. </div>
  <?php endif;?>
  <form method="post">
    <div class="form-group">
      <label for="Username">Username</label>
      <input type="text" class="form-control" id="username" name="username" placeholder="Username"  value="<?php if(isset($_POST['username'])) echo $_POST['username']; ?>">
    </div>
    <div class="form-group">
      <label for="Firstname">Firstname</label>
      <input type="text" class="form-control" id="firstname" name="firstname" placeholder="Firstname" value="<?php if(isset($_POST['firstname'])) echo $_POST['firstname']; ?>">
    </div>
    <div class="form-group">
      <label for="Lastname">Lastname</label>
      <input type="text" class="form-control" id="lastname" name="lastname" placeholder="Lastname" value="<?php if(isset($_POST['lastname'])) echo $_POST['lastname']; ?>">
    </div>
    <div class="form-group">
      <label for="Email">Email</label>
      <input type="email" class="form-control" id="email"  name="email" placeholder="Email" value="<?php if(isset($_POST['email'])) echo $_POST['email']; ?>">
    </div>
    <div class="form-group">
      <label for="Password">Password</label>
      <input type="password" class="form-control" id="password" name="password" placeholder="Password">
    </div>
    <div class="form-group">
      <label for="Confirm Password">Confirm Password</label>
      <input type="password" class="form-control" id="confirm_password" name="confirm_password" placeholder="Confirm Password">
    </div>
    <div class="form-group">
      <label for="Gender">Gender</label>
      <label class="radio-inline">
        <input type="radio" name="gender"  value="male" checked>
        Male </label>
      <label class="radio-inline">
        <input type="radio" name="gender"  value="female">
        Female </label>
    </div>
    <button type="submit" class="btn btn-primary">Register</button>
    <br><br>
  </form>
</div>