woocommerce/templates/single-product/add-to-cart/variable.php

<?php
/**
 * Variable product add to cart
 *
 * @author  WooThemes
 * @package WooCommerce/Templates
 * @version 2.4.0
 */

if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

global $product, $post;

do_action( 'woocommerce_before_add_to_cart_form' ); ?>

<form class="variations_form cart" method="post" enctype='multipart/form-data' data-product_id="<?php echo $post->ID; ?>" data-product_variations="<?php echo esc_attr( json_encode( $available_variations ) ) ?>">
	<?php do_action( 'woocommerce_before_variations_form' ); ?>

	<?php if ( ! empty( $available_variations ) || false === $available_variations ) : ?>
		<table class="variations" cellspacing="0">
			<tbody>
				<?php foreach ( $attributes as $attribute_name => $options ) : ?>
					<tr>
						<td class="label"><label for="<?php echo sanitize_title( $attribute_name ); ?>"><?php echo wc_attribute_label( $attribute_name ); ?></label></td>
						<td class="value">
							<?php
								$selected = isset( $_REQUEST[ 'attribute_' . sanitize_title( $attribute_name ) ] ) ? $_REQUEST[ 'attribute_' . sanitize_title( $attribute_name ) ] : $product->get_variation_default_attribute( $attribute_name );
								wc_dropdown_variation_attribute_options( array( 'options' => $options, 'attribute' => $attribute_name, 'product' => $product, 'selected' => $selected ) );
							?>
						</td>
					</tr>
		        <?php endforeach;?>
				<tr class="woocommerce-reset-row">
					<th>&nbsp;</th>
					<td><a class="reset_variations" href="#"><?php _e( 'Clear selection', 'woocommerce' ); ?></a></td>
				</tr>
			</tbody>
		</table>

		<?php do_action( 'woocommerce_before_add_to_cart_button' ); ?>

		<div class="single_variation_wrap" style="display:none;">
			<?php do_action( 'woocommerce_before_single_variation' ); ?>

			<div class="single_variation"></div>

			<?php do_action( 'woocommerce_before_variations_button' ); ?>
			<div class="variations_button">
				<?php woocommerce_quantity_input( array( 'input_value' => isset( $_POST['quantity'] ) ? wc_stock_amount( $_POST['quantity'] ) : 1 ) ); ?>
				<button type="submit" class="single_add_to_cart_button button alt"><?php echo esc_html( $product->single_add_to_cart_text() ); ?></button>
			</div>
			<?php do_action( 'woocommerce_after_variations_button' ); ?>

			<input type="hidden" name="add-to-cart" value="<?php echo $product->id; ?>" />
			<input type="hidden" name="product_id" value="<?php echo esc_attr( $post->ID ); ?>" />
			<input type="hidden" name="variation_id" class="variation_id" value="" />

			<?php do_action( 'woocommerce_after_single_variation' ); ?>
		</div>

		<?php do_action( 'woocommerce_after_add_to_cart_button' ); ?>

	<?php else : ?>
		<p class="stock out-of-stock"><?php _e( 'This product is currently out of stock and unavailable.', 'woocommerce' ); ?></p>
	<?php endif; ?>

	<?php do_action( 'woocommerce_after_variations_form' ); ?>
</form>

<?php do_action( 'woocommerce_after_add_to_cart_form' ); ?>