If-Else语句不读

Question

I am using Parse.com to load a certain number of points for a user. When the user redeems their points, the app should subtract that amount of points from him if he has a sufficient amount of points, but for some reason, the app says that the user always has a insufficient amount of points, even though the amount of points shown is a sufficient amount. Here is the code..

if (alertView.tag == TAG_GOODIEBAG) {

    NSLog (@"user ID:%@", [[PFUser currentUser] objectId]);

    PFQuery *query = [PFUser query];
    [query getObjectInBackgroundWithId:[[PFUser currentUser] objectId] block:^(PFObject *points, NSError *error) {
        // Do something with the returned PFObject in the gameScore variable.


        int score = [[points objectForKey:@"Points"] intValue];

        int finalpoints = score - 250;

        if (finalpoints << 0) {
            UIAlertView *alertnoerror = [[UIAlertView alloc]
                                         initWithTitle:@"Insufficient Points"
                                         message:@"You don't have enough points to redeem this item."
                                         delegate:self
                                         cancelButtonTitle:@"Dismiss"
                                         otherButtonTitles:nil];
            [alertnoerror show];
        }

        else {

        NSLog(@"%d", finalpoints);
        NSString *finalamountofpoints = [NSString stringWithFormat:@"Points: %d", finalpoints];

        label.text = finalamountofpoints;

        int goodiebagpoints = [[points objectForKey:@"GoodieBag"] intValue];

        int finalgoodiebagpoints = goodiebagpoints + 1;

        NSLog(@"%d", finalgoodiebagpoints);

        id var = [NSNumber numberWithInteger: finalpoints];
        id goodiebagid = [NSNumber numberWithInteger:finalgoodiebagpoints];
        points[@"Points"] = var;
        points[@"GoodieBag"] = goodiebagid;
        [points saveInBackground];

        if (!error) {
            UIAlertView *alertnoerror = [[UIAlertView alloc]
                                            initWithTitle:@"Success!"
                                            message:@"You have successfully redeemed your points for your Goodie Bag! Visit our office to receive your prize!"
                                            delegate:self
                                            cancelButtonTitle:@"Dismiss"
                                            otherButtonTitles:nil];
            [alertnoerror show];
        }
        }
                }];

    }

Answer 1

if (finalpoints << 0) will return true for everything except 0 .

You probably meant:

if (finalpoints < 0)

which will return true only when finalpoints is some value less than zero.

finalpoints << 0 shifts all of the bits in finalpoints left zero places. So as long as finalpoints is non-zero, it will remain non-zero after the shift, and evaluate to YES .