How to create a DLL library in C and then use it with C#?

after i have done all the neccessary coding, i have tried to add the generated c++ dll to my C# references and it keeps on prompting that i should only add valid assembly or COM references. pls help

How to create a DLL library in C and then use it with C#?
Without seeing your code and writing a short novel here, the answer you need is probably in one or all of the four URLs below. Good luck!