How can I convert this into varchar value in C#?

int RowsAffected = -1;
string MessageboxContent = string.Empty;

int EmployeeID = -1;
string Firstname = textBox2.Trim();

// rudimentary validation to make sure you have valid values
if ((int.TryParse(textBox1, out EmployeeID) && (Firstname.length > 0)) { 

  using (SqlConnection sqlcon = new SqlConnection("Data Source=.\\SQLEXPRESS;AttachDbFilename=C:\\Users\\john\\Documents\\Visual Studio 2010\\Projects\\Login\\Login\\dblogin.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True")) {
    sqlcon.Open();

    SqlCommand cmd = new SqlCommand("UPDATE tbl_employee SET Firstname= @Firstname WHERE Employee_ID= @EmployeeID", sqlcon);
    cmd.Parameters.AddWithValue("@Firstname", Firstname);
    cmd.Parameters.AddWithValue("@EmployeeID", EmployeeID);

    RowsAffected = cmd.ExecuteNonQuery();
    sqlcon.Close();
  }
}

switch (RowsAffected) {
  case -1: MessageboxContent = "Invalid data entereed"; break;
  case 0: MessageboxContent = "Employee not found, record not updated";
  case -1: MessageboxContent = "Record has been updated Successfully";
  default: MessageboxContent = string.Format("Error: {0} records updated", RowAffected); break;
}

MessageBox.Show(MessageboxContent);