To compile a C++ plug-in for Android, use the Android NDK and familiarize yourself with the steps required to build a shared library or a static library.
If you use C++ to implement the plug-in, you must declare with C linkage to avoid name mangling issues. By default, only C source files that have a .c file extension in the plug-ins have C linkage (not C++).
extern "C" {
float Foopluginmethod ();
}