develop ios app using windows 8 PC

Further to what Lesley has just said, you can now use Apple's new Swift programming language instead of, or in conjunction with, Objective-C:

https://developer.apple.com/swift/

However, Swift is still in beta as is Xcode 6 which you'll need to install to use it.

Consequently, you won't be able to submit any Swift applications to the App Store until Swift reaches version 1.0, probably later this year when iOS 8 is released.

If you want to develop your own application on Windows 8, and run it on iOS, you have two options:
1. Run Mac OSX Virtual Machine using a Virtual Machine player (such as VirtualBox). In this way, you will not need a real MAC machine, and you need to use Objective-C and Apple technologies.
You can get started by reading the following page:
https://developer.apple.com/library/ios/documentation/iPhone/Conceptual/iPhoneOSProgrammingGuide/Introduction/Introduction.html
If you already familiar with Objective-C, but you need some advanced features (OCR, Barcode, etc.), you can try using a programming toolkit that has native iOS support. You can find more information in the following pages:
http://www.codeproject.com/Articles/525537/iOS-OCR-and-Barcode-with-LEADTOOLS

2. If you are not familiar with Objective-C or Apple technologies, you can consider creating HTML5 cross platform applications. This type of applications can work on any OS (iOS, Android, Windows for Mobiles, etc.) that supports HTML5 features.
There are some good open source JavaScript and HTML5 libraries (such as JQuery, Topcoat, etc.) that support developing this kind of applications.
Also, if your application needs special features (such as Barcode, OCR, Image processing), you can use a programming toolkit (leadtools) that has strong HTML5 features that are specialized in the different fields of business.