iOS iTennis Tutorial problem

#import "iTennisViewController.h"

#define kCompMoveSpeed 15
#define kGameStateRunning 1
#define kGameStatePaused  2

#define kBallSpeedX 10
#define kBallSpeedY 10

@implementation iTennisViewController
@synthesize ball,racquet_yellow,racquet_green,player_score,computer_score,gameState,ballVelocity,tapToBegin;



/*
// The designated initializer. Override to perform setup that is required before the view is loaded.
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil {
    if ((self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil])) {
        // Custom initialization
    }
    return self;
}
*/

/*
// Implement loadView to create a view hierarchy programmatically, without using a nib.
- (void)loadView {
}
*/



// Implement viewDidLoad to do additional setup after loading the view, typically from a nib.
- (void)viewDidLoad {
    [super viewDidLoad];
	self.gameState = kGameStatePaused;
	ballVelocity = CGPointMake(kBallSpeedX,kBallSpeedY);
	[NSTimer scheduledTimerWithTimeInterval:0.05 target:self selector:@selector(gameLoop) userInfo:nil repeats:YES];
}

-(void) gameLoop {
	if(gameState == kGameStateRunning) {
		
		ball.center = CGPointMake(ball.center.x + ballVelocity.x, ball.center.y + ballVelocity.y);
		
		if(ball.center.x > self.view.bounds.size.width || ball.center.x < 0) {
			ballVelocity.x = -ballVelocity.x;
		}
		
		if(ball.center.y > self.view.bounds.size.width || ball.center.y < 0) {
			ballVelocity.y = -ballVelocity.y;
		}
	} else {
		if (tapToBegin.hidden) {
			tapToBegin.hidden = NO;
		}
	}
	if(CGRectIntersectsRect(ball.frame,racquet_yellow.frame)) {
		if(ball.center.y <racquet_yellow.center.y) {
			ballVelocity.y = -ballVelocity.y;
			NSLog(@"%f %f",ball.center, racquet_green.center);
		}
	}
	if(CGRectIntersectsRect(ball.frame,racquet_green.frame)) {
		if(ball.center.y >racquet_green.center.y) {
			ballVelocity.y = -ballVelocity.y;
		}
	}
	//Begin Simple AI
	if(ball.center.y <= self.view.center.y) {
		if(ball.center.x < racquet_green.center.x) {
			CGPoint compLocation = CGPointMake(racquet_green.center.x - kCompMoveSpeed, racquet_green.center.y);
			racquet_green.center = compLocation;
		}
		
		if(ball.center.x > racquet_green.center.x) {
			CGPoint compLocation = CGPointMake(racquet_green.center.x + kCompMoveSpeed, racquet_green.center.y);
			racquet_green.center = compLocation;
		}
	}
}

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
	if(gameState == kGameStatePaused) {
		tapToBegin.hidden = YES;
		gameState = kGameStateRunning;
	} else if(gameState == kGameStateRunning){
		[self touchesMoved:touches withEvent:event];
	}
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
	UITouch *touch = [[event allTouches] anyObject];
	CGPoint location = [touch locationInView:touch.view];
	CGPoint xLocation = CGPointMake(location.x,racquet_yellow.center.y);
	racquet_yellow.center = xLocation;
}
/*
// Override to allow orientations other than the default portrait orientation.
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation {
    // Return YES for supported orientations
    return (interfaceOrientation == UIInterfaceOrientationPortrait);
}
*/

- (void)didReceiveMemoryWarning {
	// Releases the view if it doesn't have a superview.
    [super didReceiveMemoryWarning];
	
	// Release any cached data, images, etc that aren't in use.
}

- (void)viewDidUnload {
	// Release any retained subviews of the main view.
	// e.g. self.myOutlet = nil;
}


- (void)dealloc {
    [super dealloc];
	[ball release];
	[racquet_green release];
	[racquet_yellow release];
	[player_score release];
	[computer_score release];
	[tapToBegin release];
}

@end