在9999999/10000000上,double等于0

Question

我有一个问题,我正在做一些个人研究如何工作http://www.codeproject.com/Articles/17480/Optimizing-integer-divisions-with-Multiply-Shift-i但我没有得到远,直到我得到难倒,所以代码atm应该返回大约100%的错误

        double sum = 0, div = 3;
        DateTime t1 = DateTime.Now;
        List<double> l1 = new List<double>();
        for (int a = 0; a < 10000000; a++)
        {
            sum = a / div;
            l1.Add(sum);
        }
        Console.WriteLine("Milisecond: " + DateTime.Now.Subtract(t1).TotalMilliseconds);
        t1 = DateTime.Now;
        List<double> l2 = new List<double>();
        for (int a = 0; a < 10000000; a++)
        {
            sum = a * div;
            l2.Add(sum);
        }
        Console.WriteLine("Milisecond: " + DateTime.Now.Subtract(t1).TotalMilliseconds);
        int c=0;
        int err = 0;
        for (int a = 0; a < (l1.Count < l2.Count ? l1.Count : l2.Count); a++)
        {
            c++;
            err += l1[a] != l2[a] ? 1:0;
        }
        Console.WriteLine("Error: " + 100*(err / c) + "%");

但最后一行显然返回0 9999999/10000000 = 0

我如何解决这个问题的任何想法？我最好的猜测是它的漂浮问题.(但现在我知道我的错误)

Answer 1

操作的变量声明为int,因此操作在整数上完成,结果只转换为double.

要获得双重结果,您可以:

dRes = (double)x / y;

顺便说一句,有一种更好的方法来测试代码的运行时间:

Stopwatch sw = Stopwatch.StartNew();

// ... Some code

sw.Stop();
Console.WriteLine(sw.Elapsed);