winform c# 验证数字 精度 有效位

Question

求 c# 验证精度 有效位,比如,
我要4个有效位,精度3，
那么,689.555  ->   689.5
     2.98545  ->   2.985
有效位的重要性大于精度.即以有效位为主. 

Answer 1

N次乘以10 取整，再N次除以10，N就是精度

Answer 2

#region 验证精度和有效位
        /// <summary>
        /// 验证精度和有效位
        /// </summary>
        /// <param name="value">原数字</param>
        /// <param name="ableSize">有效位</param>
        /// <param name="precision">精度</param>
        /// <returns></returns>
        public static double CheckValuePrecision(string inputdata, int ableSize, int precision)
        {
            int k = inputdata.IndexOf(".");
            string str1 = string.Empty;
            if (k > 0)
            {
                str1 = inputdata.Substring(0, k);
            }
            else
            {
                str1 = inputdata;
            }
            string str2 = inputdata.Substring(inputdata.IndexOf(".") + 1);            string factor = string.Empty;
            for (int i = 0; i < ableSize; i++)
            {
                factor += "9";
            }            if (str1.Length > ableSize)
            {
                return Convert.ToDouble(factor);
            }
            else if (str1.Length == ableSize)
            {
                return Convert.ToDouble(str1);
            }
            else
            {
                int cutLength = 0;
                if (str1 == "0")
                {
                    cutLength = ableSize;
                }
                else
                {
                    cutLength = ableSize - str1.Length;
                }
                if (str2.Length >= cutLength)
                {
                    return Convert.ToDouble(str1 + "." + str2.Substring(0, cutLength));
                }
                else
                {
                    return Convert.ToDouble(str1 + "." + str2);
                }
            }
        }
        #endregion