I am totally new in c++ and I want to use C++ dll (having header file) in c# program. please find below header file. Code: #pragma once #define DAILY_PERIOD 24*60 #define MIN_PERIOD 1 #ifdef API_DLL #define METHOD_TYPE __declspec(dllexport) #else #define METHOD_TYPE __declspec(dllimport) #endif struct Quote { unsigned long Date; float Price; float Open; float High; float Low; float Volume; float OpenInterest; }; class METHOD_TYPE CMinuteApiCallback { public: virtual int quote_notify( const char* symbol, int interval, int nMaxSize, Quotation *pQuotes, unsigned long echo)=0; }; class METHOD_TYPE CMinuteApi { public: CMinuteApi(void); int Initialise(char *serialkey, CMinuteApiCallback* callback); int GetQuote(char * symbol, int periodicity, unsigned long lasttimeupdate, unsigned long echo); int DeleteQuote(char * symbol, int periodicity); ~CMinuteApi(void); }; So please let me know how can I call all these methods in my c# program. thanks in advance