xcode openURL maps.apple.com current location to destination

xcode openURL maps.apple.com current location to destination

As a newbie im finding it fun learning Xcode. I have created a button that
when pushed opens a url which is actually opening the apple.maps and
plotting a route using this code:
-(IBAction)pushButton{
UIApplication *app = [UIApplication sharedApplication];
[app openURL:[NSURL
URLWithString:@"http://maps.apple.com/?daddr=San+Francisco,+CA&saddr=cupertino"]];
}
Im looking for the string to use use the users current location for the
starting point and then a specified address for the destination?