- (void)viewDidLoad
{
    //init the first image view
    [imageView1 setImage:[UIImage imageNamed:@"img1.jpeg"]];
    tempImageView = imageView2;
    
    //make the first image view visible and hide the second
    [imageView1 setHidden:NO];
    [imageView2 setHidden:YES];
    
    //add event handler for the page control
    [pageControl addTarget:self 
                    action:@selector(pageTurning:) 
          forControlEvents:UIControlEventValueChanged];
    
    prevPage = 0;
    [super viewDidLoad];
}

//when the page controller's value is changed
-(void) pageTurning: (UIPageControl *)pageController{
    //get the page number you can turnning to 
    
    NSInteger nextPage = [pageController currentPage];
    
    switch (nextPage){
        case 0:
            [tempImageView setImage:
             [UIImage imageNamed:@"img1.jpeg"]];
            break;
        case 1:
            [tempImageView setImage:
             [UIImage imageNamed:@"img2.jpeg"]];
            break;
        case 2:
            [tempImageView setImage:
             [UIImage imageNamed:@"img3.jpeg"]];
            break;
        case 3:
            [tempImageView setImage:
             [UIImage imageNamed:@"img4.jpeg"]];
            break;
        case 4:
            [tempImageView setImage:
             [UIImage imageNamed:@"img5.jpeg"]];
            break;
        default:
            break;
    }
    
        
    //switch the two imageviews
    if(tempImageView.tag == 0){
        tempImageView = imageView1;
        bgImageView = imageView2 ;
    }
    else{
        tempImageView = imageView2;
        bgImageView = imageView1 ;
    }
    
    
    UIViewAnimationOptions transitionOption;
    if(nextPage > prevPage)
        //--if moving from left to right
        transitionOption = UIViewAnimationOptionTransitionFlipFromLeft;
    else {
        //--if moving from right to left
        transitionOption = UIViewAnimationOptionTransitionFlipFromRight;
    }
    
    //---animate by flipping the imagees---
    [UIView transitionWithView:tempImageView 
                      duration:2.5 
                       options:(transitionOption) 
                    animations:^{
                        [tempImageView setHidden:YES];
                    }
                    completion:NULL];
    [UIView transitionWithView:bgImageView 
                      duration:2.5 
                       options:(transitionOption) 
                    animations:^{
                        [bgImageView setHidden:NO];
                    }
                    completion:NULL];
}

    //switch the two imageviews
    if(tempImageView.tag == 0){
        tempImageView = imageView1;
        bgImageView = imageView2 ;
    }
    else{
        tempImageView = imageView2;
        bgImageView = imageView1 ;
    }

    if (tempImageView.tag == 0) { 
        tempImageView = imageView2;
        bgImageView = imageView1;
    }
    else {                       
        tempImageView = imageView1;
        bgImageView = imageView2;
    }