how to make separate Connection String in c# ?

Refer link given below:
Code Project Question: Sql Connection in seperate class
Refer link given below to create a data access component:
Creating DataAccess Component for SQL Server in C#

Try using Static class and variables for this.

public static class DataAccessClass
{

    static SqlConnection objConn = new SqlConnection();


    public static SqlConnection MyConnection
    {
        get { return objConn; }

    }

    public static void OpenConnection()
    {
        string ConnectionSring = "MYCONNECTIONSTRING";
        objConn.ConnectionString = ConnectionSring;
        objConn.Open();
    }



    public static void CloseConnection()
    {
        objConn.Close();
    }



}

This is very basic structure i am describing here.
I am not doing your homework so you have to add your code and exception handling by yourself.
Once you initiate the connection

DataAccessClass.OpenConnection();

Your connection is open for throughout the application and you don't have to open it again.

I suggest that YOU MUST NEVER IMPLEMENT THIS as it is a bad practice to leave Connection open.


Better way is to open connection execute your database operations and close it immediately.

Everything that has been said before is 100% valid about opening and closing your connections. However one thing that hasn't been pointed out is that you probably shouldn't store you connection string inside a class because you will have to constantly rebuild your app if there is a change to the connection string.

You should take a look at storing the connection string in the config file so you can easily modify the connection string without having to rebuild or redeploy your app. Take a look at this article for details on how to accomplish that as well as how to access it in your application.

http://msdn.microsoft.com/en-us/library/ms254494.aspx[^]