Syntax for the zip.save(); method in C#

Question

Hi, I have been using the Ionic.zip namespace for the zipping program. But I have seen that you should provide the name of the .zip file in C# program everytime and if the user has to zip many files he cannot go the sourcecode and change the program line everytime so I copied the sourcepath to a variable & then sourcepath/destddir should be given as input to "zip.save();" method so the new zipfile is named with the same name and the path would remain same as the directory from which it has been taken from.

public void button2_Click(object sender, EventArgs e) {

        String sourcepath = System.IO.Path.GetFullPath(openFileDialog1.FileName);
        MessageBox.Show(sourcepath);
        String destdir = System.IO.Path.GetDirectoryName(openFileDialog1.FileName);
        MessageBox.Show(destdir);
        try
        {
            using (ZipFile zip = new ZipFile())
            {

               zip.AddFile(sourcepath);

               zip.Save(@"d:\todayTest2\myplate.zip");// Can I write this as zip.Save(sourcepath+ .zip); ??

              }
            label1.Text = "zipped";

}

I need to know the exact syntax of zip.save() method and Is it possible to give a variable as input to that method for saving a zip file. Thanks!