How to concatenate 2 fields in a Gravity Form?

I have 2 fields in my form for the first name and last name, and I need to get the full name in a single field. How can I combine these 2 fields into a third?

Add this code to your plugin or function file:

<?php
/*
* concatenates fields 1 and 2 into field 3 for form #10
*/
add_action( 'gform_pre_submission_10', 'wpster_get_fullname' );
function wpster_get_fullname($form) {
	$_POST['input_3'] = rgpost('input_1').' '.rgpost('input_2');
}
?>

If you want to repeat the same operation for several forms, use this syntax:

<?php
add_action( 'gform_pre_submission', 'wpster_get_fullname' );
function wpster_get_fullname($form) {
	// form #1 Contact
	if ( $form['id'] == 1 ) {
		$_POST['input_9'] = rgpost('input_1').' '.rgpost('input_3');
	}
	// form #3 Reservations
	if ( $form['id'] == 3 ) {
		$_POST['input_18'] = rgpost('input_1').' '.rgpost('input_3');
	}

	/* complete with other forms... */
}
?>