开学时间为2009年2月18日，计算当前日期是第几周

加一label1，用来显示第几周，在加一个button，点击表示计算

代码：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace WindowsFormsApplication2
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        private string s = "2009-2-18";
        private int WeekOfYear(string date)
        {
            DateTime curDay = Convert.ToDateTime(date);
            DateTime oldDay = Convert.ToDateTime(s);
            int days1 = oldDay.DayOfYear;//获取开学时间离元旦的天数
            int days2= curDay.DayOfYear;//获取目前时间离元旦的天数
            int days = days2 - days1;
            label3.Text = days.ToString();
            int daysOutOneWeek = days;
            if (daysOutOneWeek <= 0)
            {
                return 1;
            }
            else
            {
                int weeks = daysOutOneWeek / 7;
                if (daysOutOneWeek % 7 != 0)
                    weeks++;
                return weeks + 1;
            }
        }
        private void button1_Click(object sender, EventArgs e)
        {
            string t;
            int m;    
            t = "2009-2-22";
            m=WeekOfYear(t);
            label1.Text = m.ToString();
        }
    }
}