自定义datetime日期累加

//传入当前时间，和是否是闰年，返回+1天后的日期   

public DateTime Mon(DateTime dt, bool ren)
    {
        int year = dt.Year;
        int mon = dt.Month;
        int day = dt.Day;
        day = day + 1;
        switch (mon)
        {
            case 1:
                if (day > 31)
                {
                    day = 1;
                    mon = mon + 1;
                }
                break;
            case 2:
                if (ren)
                {
                    if (day > 29)
                    {
                        day = 1;
                        mon = mon + 1;
                    }
                }
                else
                {
                    if (day > 28)
                    {
                        day = 1;
                        mon = mon + 1;
                    }
                }
                break;
            case 3:
                if (day > 31)
                {
                    day = 1;
                    mon = mon + 1;
                }
                break;
            case 4:
                if (day > 30)
                {
                    day = 1;
                    mon = mon + 1;
                }
                break;
            case 5:
                if (day > 31)
                {
                    day = 1;
                    mon = mon + 1;
                }
                break;
            case 6:
                if (day > 30)
                {
                    day = 1;
                    mon = mon + 1;
                }
                break;
            case 7:
                if (day > 31)
                {
                    day = 1;
                    mon = mon + 1;
                }
                break;
            case 8:
                if (day > 31)
                {
                    day = 1;
                    mon = mon + 1;
                }
                break;
            case 9:
                if (day > 30)
                {
                    day = 1;
                    mon = mon + 1;
                }
                break;
            case 10:
                if (day > 31)
                {
                    day = 1;
                    mon = mon + 1;
                }
                break;
            case 11:
                if (day > 30)
                {
                    day = 1;
                    mon = mon + 1;
                }
                break;
            case 12:
                if (day > 31)
                {
                    day = 1;
                    mon = mon + 1;
                    year = year + 1;
                }
                break;
        }

        DateTime dm = new DateTime();
        dm = Convert.ToDateTime(year.ToString() + "-" + mon.ToString() + "-" + day.ToString());
        return dm;
    }