The choice of your development language may force you to choose one API over the other. The C API is limited to development languages that can create compiled DLLs with true function entry points. C, C++, and even Pascal are good examples of this. Visual Basic can create DLLs, but these DLLs are termed OLE DLLs. These DLLs do not have true function entry points that can be accessed by direct function calls. Instead, these DLLs implement OLE interfaces that can be called by other applications (including Microsoft Excel). If you develop in Visual Basic, you will need to use the OLE Automation interface.