how can I use vairable with case

I assume you mean something like this

string x = "MyMachine";
            string y = "YourMachine";
            string na = System.Environment.MachineName;
            switch (na)
            {
                case x:

            }

I am afraid this is not possible. You will have to supply the proper string like this:

string na = System.Environment.MachineName;
           switch (na)
           {
               case "MyMachine":
                   //do something
                   break;
               case "YourMachine":
                   //do something else
                   break;

           }

If you could tell us more about what you would like to achieve we might be able to help more.

In answer to your comment, I would change this to use an If construct, something like this:

StreamReader srFrom = new StreamReader(@"your file path");
            string na = System.Environment.MachineName;
            string name = srFrom.ReadLine();
            srFrom.Close();
            if (na == name)
            {
                //Do something
            }
            else
            {
                //Do something else
            }

Hope this helps

That is how switch condition works in C#. It expects constant value for case.

In case if you declare your variables as constant as shown in below code, Then it won't give you error, But it will make no ddifference with hard coded values.

string na = System.Environment.MachineName;
const string variable1 = "ABC";
const string variable2 = "XYZ";
switch (na)
{
    case variable1:
        //Come code
        break;
    case variable2:
        //Come other code
        break;
}