How can I add alphanumeric, numeric and email validate validation in my custom form?

function form_example_form($form, &$form_state) {

$form['empcode'] = array(
  '#weight' => '0',
  '#required' => '1',
  '#type' => 'textfield',
  '#title' => t('Employee Code'),
);
$form['empname'] = array(
  '#weight' => '1',
  '#required' => '1',
  '#type' => 'textfield',
  '#title' => t('Employee Name'),
);
$form['empemail'] = array(
  '#weight' => '2',
  '#required' => '0',
  '#type' => 'textfield',
  '#title' => t('Employee Email'),
);
$form['empdesignation'] = array(
  '#weight' => '3',
  '#required' => '1',
  '#type' => 'textfield',
  '#title' => t('Employee Designation'),
);
$form['mobile'] = array(
  '#weight' => '4',
  '#required' => '0',
  '#type' => 'textfield',
  '#title' => t('Mobile No.'),
);
$form['ipphone'] = array(
  '#weight' => '5',
  '#required' => '0',
  '#type' => 'textfield',
  '#title' => t('IP Phone'),
);
$form['qualifications'] = array(
  '#weight' => '6',
  '#required' => '0',
  '#type' => 'textfield',
  '#title' => t('Qualifications'),
);
$form['profile'] = array(
  '#weight' => '7',
  '#required' => '0',
  '#type' => 'textarea',
  '#title' => t('Profile'),
);
$form['file'] = array(
  '#weight' => '8',
  '#type' => 'file',
  '#size' => '30',
  '#title' => t('Employee Photo'),
);
$form['captcha'] = array(
  '#weight' => '9',
  '#type' => 'captcha',
  '#captcha_type' => 'captcha/Math',
);
 $form['submit'] = array(
     '#weight' => '10',
    '#type' => 'submit',
    '#value' => t('Submit'),
  );

return $form;

}


function form_example_form_validate($form, &$form_state) {
  /*if (!($form_state['values']['price'] > 0)){
    form_set_error('price', t('Price must be a positive number.'));
  }*/
 // print('<pre>'.print_r($form_state['values'],1).'</pre>');
  //die();
 $file = file_save_upload('file', array(
    'file_validate_is_image' => array(),
    'file_validate_extensions' => array('png gif jpg jpeg'),
  ));
  if ($file) {
    if ($file = file_move($file, 'public://')) {
      $form_state['values']['file'] = $file;
    }
    else {
      form_set_error('file', t('Failed to write the uploaded file the site\'s file folder.'));
    }
  }
  else {
    form_set_error('file', t('No file was uploaded.'));
  }
}

i want to add advance level validations so that no one enter special characters to these form fields. Currently required is working.