Call a stored procedure with parameter in c#

It’s pretty much the same as running a query. In your original code you are creating a command object, putting it in the cmd variable, and never use it. Here, however, you will use that instead of da.InsertCommand.

Also, use a using for all disposable objects, so that you are sure that they are disposed properly:

private void button1_Click(object sender, EventArgs e) {
  using (SqlConnection con = new SqlConnection(dc.Con)) {
    using (SqlCommand cmd = new SqlCommand("sp_Add_contact", con)) {
      cmd.CommandType = CommandType.StoredProcedure;

      cmd.Parameters.Add("@FirstName", SqlDbType.VarChar).Value = txtFirstName.Text;
      cmd.Parameters.Add("@LastName", SqlDbType.VarChar).Value = txtLastName.Text;

      con.Open();
      cmd.ExecuteNonQuery();
    }
  }
}