日期加1程序

#region 日期day自动加1
        /// <summary>
        /// 将当前日期加1天
        /// </summary>
        /// <param name="str">输入日期,如20120101</param>
        /// <returns></returns>
        public static string dateAdd1(string str)
        {
            //内容分解
            int year = int.Parse(str.Substring(0, 4));
            int month = int.Parse(str.Substring(4, 2));
            int day = int.Parse(str.Substring(6));
            if (month == 12)
            {
                if (day > 31)
                {
                    MessageBox.Show("进行日期自加1时,输入的day大于31");
                    return "";
                }
                //若为最后一天,则年数加1
                if (day == 31)
                {
                    return (year + 1).ToString() + "0101";
                }
                else
                    day++;
            }
            else if(month ==1 || month ==3 || month ==5 ||month ==7 || month ==8 || month ==10)
            {
                if (day > 31)
                {
                    MessageBox.Show("进行日期自加1时,输入的day大于31");
                    return "";
                }
                //月数为31天
                if (day == 31)
                {
                    if(month!=10)
                        return year.ToString() + "0"+(month + 1).ToString() + "01";
                    else
                        return year.ToString() + (month + 1).ToString() + "01";
                }
                else
                {
                    day++;
                }
            }
            else if(month ==2)
            {
                //2月份
                int xianzhi = 28;
                if (year % 4 == 0)
                    xianzhi = 29; //闰年2月份为29天
                if (day > xianzhi)
                {
                    MessageBox.Show("2月份进行日期自加1时,输入的day大于"+xianzhi.ToString());
                    return "";
                }

                if (day == xianzhi)
                {
                    return year.ToString() + "0" + (month + 1).ToString() + "01";
                }
                else
                    day++;
            }
            else
            {
                //每月30天的情形
                if (day > 30)
                {
                    MessageBox.Show("进行日期自加1时,输入的day大于31");
                    return "";
                }
                if (day == 30)
                {
                    if(month>8) //9+1为10，所以，9月份前也不用加0
                        return year.ToString() + (month + 1).ToString() + "01";
                    else
                        return year.ToString()+"0" + (month + 1).ToString() + "01";
                }
                else
                    day++;
            }
            string strd=day.ToString();
            string strm=month.ToString();
            if(day<10)
            {
                strd= "0"+strd;
            }
            if (month < 10)
            {
                strm = "0" + strm;
            }
            return year.ToString() + strm + strd;
        }