How to save username & password locally in .Net application?

I am creating a login screen for which i have to save username & password locally so that next time when user login it doesn't ask for login .

I have used this code to save

Configuration config = System.Configuration.ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);

config.AppSettings.Settings.Add("UserName"username);

config.AppSettings.Settings.Add("Password ",userpasssword);

config.Save();

System.Configuration.ConfigurationManager.RefreshSection("appSettings");

I am working in debug mode in VS2015 , first the username & password are written to myapp.vshost.exe.config file & once i close application , it is not saved . So, next time when user login ,again it will ask for password .

My question are -:How it will be saved permanently so that it exists even if application is closed so that next time when user login it doesn't ask for login credentials ?

is my approach correct or not ?