How to Create Drop-Down Select Lists in Joomla

<?php
// Set some default value to be the selected item in the dropdown list
$default = 3;

// An array of $key=>$value pairs 
$cities = array(1 => 'Rawalpindi', 2 => 'Islamabad', 3 => 'Lahore', 4 => 'Karachi');

// Initialize array to store dropdown options 
$options = array();

foreach($cities as $key=>$value) {

  // Create $value 
  // For Joomla 3
    $options[] = JHTML::_('select.option', $key, $value);

  // For Joomla 4, Joomla 5+
  // Please also add use Joomla\CMS\HTML\HTMLHelper; 
  // At the top of file but after namespace if it is present
	$options[] = HTMLHelper::_('select.option', $key, $value);
}

// Create <select name="city" class="inputbox"></select> 

// For Joomla 3
$dropdown = JHTML::_('select.genericlist', $options, 'city', 'class="inputbox"', 'value', 'text', $default);

// For Joomla 4, Joomla 5+
$attribs = null;
echo HTMLHelper::_('select.genericlist', $options, 'city', $attribs, 'value', 'text', $default);

// Output created <select> list
echo $dropdown;
?>