No of files in the Folder in Particular file Type in the C#.Net

The following function returns no of files in the particular in the particular folder in the C#.net
Declaration part:

       public static int chknofiles;

Function Part:

public static int countoffiles(string filepath, string fileextension)
        {

            string[] fsDir = Directory.GetFiles(filepath);
            foreach (string f in fsDir)
            {
                string fName = f.Substring(filepath.Length + 1);
                string[] fileExt = fName.Split('.');
                if (fileExt[1] == fileextension)
                {
                    chknofiles = chknofiles + 1;
                }
            }

            return chknofiles;
        }

How to use this function in the C#.net ?

int chkvalue = countoffiles(txtBrowsFile.Text, "txt");
            MessageBox.Show(chkvalue.ToString());

Here, Chkvalue is an object.
countoffiles is a function
txtBrowseFiles.Text is a Input value(Specify the Path)
txt is a file extension.