c# 计算星座

 public string xz(DateTime birthday)
        {
            float birthdayF = 0.00F;

            if (birthday.Month == 1 && birthday.Day < 20)
            {
                if (birthday.Day < 10)
                    birthdayF = float.Parse(string.Format("13.0{0}", birthday.Day));
                else
                    birthdayF = float.Parse(string.Format("13.{0}", birthday.Day));
            }
            else
            {
                if (birthday.Day < 10)
                    birthdayF = float.Parse(string.Format("{0}.0{1}", birthday.Month, birthday.Day));
                else
                    birthdayF = float.Parse(string.Format("{0}.{1}", birthday.Month, birthday.Day));
            }

            float[] atomBound = { 1.20F, 2.20F, 3.21F, 4.21F, 5.21F, 6.22F, 7.23F, 8.23F, 9.23F, 10.23F, 11.21F, 12.22F, 13.20F };
            string[] atoms = { "水瓶座", "双鱼座", "白羊座", "金牛座", "双子座", "巨蟹座", "狮子座", "处女座", "天秤座", "天蝎座", "射手座", "魔羯座" };

            string ret = "";
            for (int i = 0; i < atomBound.Length - 1; i++)
            {
                if (atomBound[i] <= birthdayF&&atomBound[i+1]> birthdayF)
                {
                    ret = atoms[i];
                    break;
                }
            }
            return ret;
        }