About block's argument

Objective-C Programming (2nd Edition) 28. Blocks
1 

devowelizer = ^(id string, NSUInteger i, BOOL *stop) {
            NSRange yRange = [string rangeOfString:@"y" options:NSCaseInsensitiveSearch];
            if (yRange.location != NSNotFound) {
                *stop = YES;
                return;
            }

this is part of code, but i don’t understand of this expression.
*stop = YES;

stop is a pointer. there is BOOL pointer?
this is C’expression?
can you tell me more expression?

2

Means assign YES as the value for the stop pointer. Remove the asterisk and you should get an error.