1) https://www.c-sharpcorner.com/UploadFile/tanmayit08/unmanaged-cpp-dll-call-from-managed-C-Sharp-application/
or https://stackoverflow.com/questions/7232259/c-sharp-importing-c-dll
2) https://social.msdn.microsoft.com/Forums/vstudio/en-US/57dd804c-a5b7-428b-be61-eccda3c8bd9d/how-to-import-native-c-dll-into-c-project?forum=csharpgeneral
3) https://www.codeproject.com/Questions/107152/Using-a-C-dll-in-a-C-application