C#中保留两位小数但不四舍五入的最优做法

多种做法比较

    class Program_保留两位小数但不四舍五入
    {
        static void Main(string[] args)
        {
            Helper.Run(delegate ()
            {
                method1();
            }, 1000000, " 1.先乘后除，再强制类型转换 ");

            Helper.Run(delegate ()
            {
                method2();
            }, 1000000, " 2.使用substring截取字符串，然后转换 ");

            Helper.Run(delegate ()
            {
                method4();
            }, 1000000, " 4.使用math.floor ");

            Helper.Run(delegate ()
            {
                method5();
            }, 1000000, " 5.使用正则来处理字符串数据，然后再类型转换 ");

            Console.ReadKey();
        }

        const double num = 15.1257;

        static void method1()
        {
            var tmp = (int)(num * 100) / 100.00;
        }

        static void method2()
        {
            var str = (num).ToString();
            var tmp = double.Parse(str.Substring(0, str.IndexOf('.') + 3));
        }

        //static void method3()
        //{
        //    var tmp = double.Parse((num).ToString("#0.00"));
        //}

        static void method4()
        {
            var tmp = Math.Floor(num * 100) / 100.00;
        }

        static void method5()
        {
            var tmp = double.Parse(Regex.Match(num.ToString(), @"[\d]+.[\d]{0,2}").Value);
        }

        //结果：method1 最快，而使用系统的方法或者字符串截取的方法都会慢一些
    }

帮助类

    public static class Helper
    {
        public static void Run(Action action, int stepTotal = 10000, string description = "")
        {
            DateTime startTime = DateTime.Now;
            for (int i = 0; i < stepTotal; i++)
            {
                action();
            }
            DateTime endTime = DateTime.Now;
            var ts = endTime - startTime;
            Console.WriteLine(description + "_运行“" + stepTotal.ToString() + "”次耗时：" + (endTime - startTime).TotalMilliseconds.ToString() + "ms");
        }
    }