嵌套随机生成器不是随机的

Question

I have the following code. Random r works and gets me about 10% into the if. However rr doesn't seem to work. It always returns 0. What am I doing wrong?

I want to choose between two choices randomly only 10% of the time. This is in an asp.net app. The code gets executed on button click.

        Random r = new Random();
        Random rr = new Random();

        int randomnum = r.Next(0, 100);
        if (randomnum <= 10)
        {

            int randompick = rr.Next(0, 2);
            if (randompick == 0)
            {

Answer 1

If you are happy with the outer loop's randomness, consider

int randompick = randomnum % 2;

instead of the nested Random object.

Answer 2

您可以将相同的Random对象用于两个随机选择，对吗？

Answer 3

As noted, you should use just one pseudorandom stream and instantiate it just once. I'd struct my solution along these lines:

class SomeWidget
{
    private static Random rng ;

    static SomeWidget()
    {
        rng = new Random() ;
        return ;
    }

    public SomeWidget()
    {
        return ;
    }

    public int DoOneThing90PercentOfTheTimeAndSomethingElseTheRestOfTheTime()
    {
        int rc ;
        int n = rng.Next() % 10 ; // get a number in the range 0 - 9 inclusive.
        if ( n != 0  ) // compare to whatever value you wish: 0, 1, 2, 3, 4, 5, 6, 8 or 9. It makes no nevermind
        {
             rc = TheNinetyPercentSolution() ;
        }
        else
        {
            rc = TheTenPercentSolution() ;
        }
        return rc ;
    }

    private int TheTenPercentSolution()
    {
        int rc ;
        int n = rng.Next() % 2 ;
        if ( n == 0 )
        {
            rc = DoOneThing() ;
        }
        else
        {
            rc = DoAnotherThing() ;
        }
        return rc ;
    }

    private int DoOneThing()
    {
        return 1;
    }

    private int DoAnotherThing()
    {
        return 2 ;
    }

    private int TheNinetyPercentSolution()
    {
        return 3 ;
    }

}