calendar days in a month

When you say 'working days' I assume you mean Monday to Friday.

I don't really understand the rest of the question but the following code assumes that if you enter a month number (1 to 12) in the textbox and then click it, the number of working days in that month in the current year is calculated and assigned to the label:

        private void textox1_Click(object sender, EventArgs e)

        {

            int month;

            int.TryParse(textBox1.Text, out month);

            if (month < 1 || month > 12)

            {

                MessageBox.Show("Not a valid month. Please re-enter");

                textBox1.Focus();

                return;

            }

            DateTime dt = new DateTime(DateTime.Today.Year, month, 1);

            int workingDays = 0;

            for (int i = 0; i < DateTime.DaysInMonth(dt.Year, month); i++)

            {

                if (dt.DayOfWeek != DayOfWeek.Saturday && dt.DayOfWeek != DayOfWeek.Sunday)

                {

                    workingDays++;

                }

                dt = dt.AddDays(1);

            }

            label1.Text = workingDays.ToString();

        }