This section discusses the implementation of the application based on the ideas outlined above. Our primary target platform is the iPhone, where the Objective-C language is mandatory for graphical user interface (GUI) development, but we chose to write most of our application in C++ in order to facilitate its porting to other mobile platforms. GCC 4.2 is the default internal compiler in the Xcode development environment, and it can be used to compile C++ source files in Objective-C++ mode and link with the generated object files. Consequently, the GUI that has to be written in Objective-C can call regular C++ code, and a high degree of platform independence can be achieved. Note that we used iPhone OS v. 3.1.3 for development.