XCode - Referring to a UIImageView variable through another string variable?

Is it possible to use a string variable to refer to a UIImageView variable and change the image? The string variable is created by adding an "s" to the start of the tag of the button pressed. This is also the name of a specific UIImageView.

So one of the UIImageView declared in the .h file looks like this:

@property (retain, nonatomic) IBOutlet UIImageView *s11;

And in the .m file so far:

NSString *lastpressnum = [@(sender.tag) stringValue];
NSString *lastpressed = [NSString stringWithFormat:@"%s%@", "s", lastpressnum];
[lastpressed setImage:image];