Random number generator in c# - again

[Piotr 'Zenobius' Baranowski]

Hello :-)

I've got lame begginer question about generating different random
numbers in C# ;-)

First, some code:
public int test(int lb)
{
int count = 0;
Random randSeed = new Random();

for(int i=0;i<lb;i++)
{
double test = randSeed.NextDouble();
if(test>0.49) {
count++;
}
}
return count;
}

The code _should_ give me all positive scores of 'lb' throws of coin.
And it does. But when called couple of times in the "same" time, like:

test(23); test(12); test(45);

it generates the same scores..

How do i hop over it in C# ? ;-)
--
Best regards.. or not..
Piotr 'Zenobius' Baranowski

[Mark R. Dawson]

Hi Piort,
I am not sure what you mean by "hop over it" but you can try to make it
more random by adding a seed to the constructor of the random class, or
create the random class outside of your test method and pass it in so that
all counts use the same random object i.e.

Random r = new Random((int)DateTime.Now.Ticks);

test(23, r);
test(15, r);
test(45, r);

Or if you want truley random numbers you might want to try using
System.Security.Cryptography.RandomNumberGenerator which will give you better
results, but I believe will be slower.

Hope that helps
Mark R Dawson

"Piotr 'Zenobius' Baranowski" wrote:

Hello :-)

I've got lame begginer question about generating different random
numbers in C# ;-)

First, some code:
public int test(int lb)
{
int count = 0;
Random randSeed = new Random();

for(int i=0;i<lb;i++)
{
double test = randSeed.NextDouble();
if(test>0.49) {
count++;
}
}
return count;
}

The code _should_ give me all positive scores of 'lb' throws of coin.
And it does. But when called couple of times in the "same" time, like:

test(23); test(12); test(45);

it generates the same scores..

How do i hop over it in C# ? ;-)
--
Best regards.. or not..
Piotr 'Zenobius' Baranowski

[shiv_koirala]

Hi

System.random namespace

Random r = new Random()

I think it also has facility to generate random numbers in integer ,
double etc etc

Shivprasad Koirala
C# , VB.NET , SQL SERVER , ASP.NET Interview Questions
http://www.geocities.com/dotnetinterviews/

[Jon Skeet [C# MVP]]

Piotr 'Zenobius' Baranowski <ze******@zeno.pl> wrote:

<snip>

The code _should_ give me all positive scores of 'lb' throws of coin.
And it does. But when called couple of times in the "same" time, like:

test(23); test(12); test(45);

it generates the same scores..

How do i hop over it in C# ? ;-)

Just create a single Random and use it repeatedly. By default, the
current time is used for the initial seed for a new Random instance. If
you create two Randoms at the same time (as you are doing, effectively)
you'll get the same results multiple times.

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

[Piotr 'Zenobius' Baranowski]

Jon Skeet [C# MVP] wrote:

Just create a single Random and use it repeatedly. By default, the
current time is used for the initial seed for a new Random instance. If
you create two Randoms at the same time (as you are doing, effectively)
you'll get the same results multiple times.

This works the same, 2-4 scores are the same ;-)

I just wanted to create function, that simulates real k2 rolls.. now i'm
using Random.Next(lb+1), and it works fine.
--
Best regards.. or not..
Piotr 'Zenobius' Baranowski

[Jon Skeet [C# MVP]]

Piotr 'Zenobius' Baranowski <ze******@zeno.pl> wrote:

Just create a single Random and use it repeatedly. By default, the
current time is used for the initial seed for a new Random instance. If
you create two Randoms at the same time (as you are doing, effectively)
you'll get the same results multiple times.
This works the same, 2-4 scores are the same ;-)

In that case, you're either not actually using a single random, or
you're just being unlucky in seeing the same values.
I just wanted to create function, that simulates real k2 rolls.. now i'm
using Random.Next(lb+1), and it works fine.

Righto.

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too