Set product quantity value through URL parameter in WooCommerce

product-quantity-through-url-parameter-for-woocommerce.php

<?php // For implementation instructions see; https://aceplugins.com/how-to-add-a-code-snippet/

/**
 * Product quantity through URL parameter.
 *
 * Allow for setting a suggested product quantity in the product quantity field by adding
 * a &quantity=5 URL parameter.
 *
 * @param array $args Original arguments.
 * @param WC_Product $product Product being viewed.
 * @return mixed Modified arguments.
 */
function ace_product_quantity_through_url( $args, $product ) {
	if ( isset( $_GET['quantity'] ) && ! isset( $_POST['quantity'] ) ) {
		$args['input_value'] = absint( $_GET['quantity'] );
    }

    return $args;
}
add_filter( 'woocommerce_quantity_input_args', 'ace_product_quantity_through_url', 10, 2 );