How i Define Connection String in any class file

Question

Dear Sir/Mam

 

Please tell me how can i define connection string in my class file.i do not want to describe it in web.config for Database Security.

 

//SqlConnection mainConnectionString = new SqlConnection();

string str = "server=192.1.1.1;database=db;user id=sa;password=.com;";

SqlConnection mainConnectionString = new SqlConnection(str);

// mainConnectionString = ConfigurationManager.ConnectionStrings["ConnectionString"].ToString();

// mainConnectionString.ConnectionString=("server=192.1.1.1;database=db;user id=sa;password=.com;").ToString();

string sam =Convert.ToString( mainConnectionString);

i use all this thing but project not working but if use 

// mainConnectionString = ConfigurationManager.ConnectionStrings["ConnectionString"].ToString();

 ConnectionString from web.config 

then its working fine.

 

please tell me  how i solve this problem or any alternative  to secure dB USER and password.

or any decrypt or encrypt  method use for web.config.