It is easy with the SKStoreProductViewController as redent84 answered and it is introduced in iOS 6+. With that users can buy your other apps right within the application.
First add StoreKit.framework to your project and add #import to header file.
Then find the Apple id of the app by going in iTunes connect manage applications and clicking on app will show you apple id and other details and pass that to the SKStoreProductViewController.
Below is the code
#import "ViewController.h"
#import <StoreKit/SKStoreProductViewController.h>
@interface ViewController ()<SKStoreProductViewControllerDelegate>
@end
@implementation ViewController
- (void)viewDidLoad
{
[super viewDidLoad];
[self showMyApps];
}
-(void)AppStoreAction:(id)sender{
NSDictionary *appParameters = [NSDictionary dictionaryWithObject:@"533886215"
forKey:SKStoreProductParameterITunesItemIdentifier];
SKStoreProductViewController *productViewController = [[SKStoreProductViewController alloc] init];
[productViewController setDelegate:self];
[productViewController loadProductWithParameters:appParameters
completionBlock:^(BOOL result, NSError *error)
{
}];
[self presentViewController:productViewController
animated:YES
completion:nil];
}
-(void)productViewControllerDidFinish:(SKStoreProductViewController *)viewController
{
[self dismissViewControllerAnimated:YES completion:nil];
}
@end
In earlier versions you could link to the App Store: [[UIApplication sharedApplication] openURL:[NSURL URLWithString:@"http://itunes.apple.com/de/artist/apple/id284417353?mt=12"]] but with this once you exit app you cannot go back to your app.
But with this SKProductViewController you can hit cancel button and go back to your app.
Hope it helps.