<div class="login_form">
<div class="container">
  <h1>Entrar</h1>
  <div class="col-lg-4 well">
    <?php if(isset($errorLogin)) { echo
      '<div class="alert alert-danger" role="alert">
      <span class="glyphicon glyphicon-exclamation-sign" aria-hidden="true"></span>
      <span class="sr-only">Error:</span>'.$errorLogin.
      '</div>'
    ;}?>
    <div class="row">
      <form  method="POST" action="login.php">
        <div class="col-sm-12">
          <div class="form-group">
            <label>E-mail</label>
            <div class="input-group">
              <span class="input-group-addon"><span class="glyphicon glyphicon-user"></span></span>
              <input type="text" class="form-control" id="loginEmail" name="loginEmail">
            </div>
          </div>
          <div class="form-group">
            <label>Senha</label>
              <div class="input-group">
                <span class="input-group-addon"><span class="glyphicon glyphicon-lock"></span></span>
                <input type="text" class="form-control" id="loginPassword" name="loginPassword">
              </div>
          </div>
          <input type="submit" name="buttonLogin" id="buttonLogin" value="Entrar" class="btn btn-lg btn-info"></input>
          <label>ou </br></label><label><a id="showRegister">Criar conta</a></label>
        </div>
      </form>
    </div>
   </div>
</div>
</div>

<div class="register_form">
  <div class="container">
    <h1>Cadrastre-se</h1>
    <div class="col-lg-6 well">
      <?php if(isset($errorRegister)) { echo
          '<div class="alert alert-danger" role="alert">
          <span class="glyphicon glyphicon-exclamation-sign" aria-hidden="true"></span>
          <span class="sr-only">Error:</span>'.$errorRegister.'
          </div>'
      ;}?>
      <div class="row">
        <form method="POST" action="login.php">
          <div class="col-sm-12">
            <div class="row">
              <div class="col-sm-6 form-group">
                <label>Nome</label>
                <input type="text" class="form-control" id="registerName" name="registerName">
              </div>

              <div class="col-sm-6 form-group">
                <label>Sobrenome</label>
                <input type="text" class="form-control" id="registerLastName" name="registerLastName">
              </div>
            </div>

          <div class="form-group">
            <label>E-mail</label>
            <input type="email" class="form-control" id="registerEmail" name="registerEmail">
          </div>

          <div class="row">
            <div class="col-sm-6 form-group">
              <label>Senha</label>
              <input type="password" class="form-control" id="registerPassword" name="registerPassword">
            </div>
            <div class="col-sm-6 form-group">
              <label>Confirmar Senha</label>
              <input type="password" class="form-control" id="registerRePassword" name="registerRePassword">
            </div>
          </div>
          <input type="submit" name="buttonRegister" id="buttonRegister" value="Cadrastre-me" class="btn btn-lg btn-info"></input>
          <label>ou </br></label><label><a id="showLogin">Entrar</a></label>
        </div>
      </form>
    </div>
  </div>
</div>

<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>

<script type="text/javascript">
  $(function(){
    $('#showRegister').click(function() {
        $('.login_form').hide();
        $('.register_form').show();
        return false;
    });

    $('#showLogin').click(function() {
        $('.register_form').hide();
        $('.login_form').show();
        return false;
    });
  });
</script>

<?php
if (isset($_POST['buttonRegister'])) {
    $name = $_POST['registerName'];
    $lastName = $_POST['registerLastName'];
    $email = $_POST["registerEmail"];
    $password = $_POST["registerPassword"];
    $rePassword = $_POST['registerRePassword'];

    if (empty($name) || empty($lastName) || empty($email) || empty($password) || empty($rePassword)) {
        $errorRegister = "<b>Nome</b>, <b>Sobrenome</b>, <b>Email</b>, <b>Senha</b> e <b>Confirmar Senha</b> são necessários.";
    }
 }

if (isset($_POST['buttonLogin'])) {
    $email = $_POST["loginEmail"];
    $password = $_POST["loginPassword"];

    if (empty($email) && empty($password))
        $errorLogin = "<b>E-mail</b> e <b>Senha</b> estão em branco";
    else if (empty($email))
       $errorLogin = '<b>E-mail</b> está em branco';
    else if (empty($password))
       $errorLogin = '<b>Senha</b> está em branco';
}