Block 代替for循环

  NSDictionary *aDictionary = [[NSDictionary alloc]initWithObjectsAndKeys:@"tom",@"",@"alex",@"",@"josen",@"", nil];
        [aDictionary enumerateKeysAndObjectsUsingBlock:^(id key, id value, BOOL *stop) {
            NSLog(@"value for key %@ is %@", key, value);
            if ([@"" isEqualToString:key]) {
                *stop = YES; }
        }];

        NSArray *aArray = [[NSArray alloc]initWithObjects:@"",@"",@"",@"",@"", nil];
        [aArray enumerateObjectsUsingBlock:^(id obj, NSUInteger index, BOOL *stop){
             NSLog(@"----%@ ---%ld",[aArray objectAtIndex:index],index);
            if (index == ) {
                *stop = YES;

            }
        }];