from the question title is there any way to connect to the database server without using string connection?
I don't wont to but the connection string in the code I want another way.
Is it possible no matter what is the database engine is.
I am building a Windows Form Application using C#.
I mean something like trusted device or windows authentication or by butting a program on server side to do the authentication
You Can't. You must have a connection string to provide the location of the server and the database name.
If you need to hide the Credentials because you're afraid of Reverse Engineering your code, then you have 2 options:
1 - Use integrated Security (Docs).
Also, you might find this Article helpful.