How to Convert IPA to C Source
At the core of iPhone application (IPA) files is the C-based object-oriented programming language called Cocoa Touch. Since Cocoa Touch-created IPA files are programmed using the C programming language, viewing an IPA's source code is a simple matter of decrypting the IPA and breaking it down into its respective files, directories and C modules, and then opening the individual code files that you wish to view. If you're an iPhone developer and wish to learn how your favorite applications work, knowing how to view an IPA's source code can be very handy.
Launch the iTunes desktop application and click "Applications" in the left menu. Navigate to the application whose source code you wish to view and right-click its icon. Select "Show in Windows Explorer" if you're using a Windows-based computer or "Show in Finder" if you're using a Mac.
Copy the application from the folder and then paste it to your desktop.
Right-click the pasted application and change the file extension from "IPA" to "ZIP."
Double-click an IPA file that has been changed to "ZIP" and allow the system to decrypt and extract its individual files and code.
Double-click the folder that was automatically created by the previous step and locate the portion of the application's C code that you wish to view. Open the code in your preferred code-editing application.