You may easily do it using #define preliminarily defined in the compiler. The following is the code that shows in what mode a project is being built – 32-bit mode or 64-bit mode (AMD64 or Intel 64) or in Itanium mode.
#if defined _M_IX86
cout << _T(" (x86)");
#elif defined _M_X64
cout << _T(" (x64)");
#elif defined _M_IA64
cout << _T(" (Itanium)");
#endif