Random Number Generating

  • Thread starter Thread starter Leon
  • Start date Start date
L

Leon

I need a program that generate 5 non-duplicates random number between 1-10
as string values store in an array.

Do anybody know of any good books or websites that explain how to generator
random numbers using asp.net? I know about the random namespace within .net,
but
I need a reference to some code that do the similar stated function above.

Plus If you have any coding practice ideas for the above defined project
please share them.

Thanks!
 
Leon,

I would use the Random class to do this. It seeds itself off the time
normally.

If you need a cryptographically secure random number generator, then
check out the RNGCryptoServiceProvider class in the
System.Security.Cryptography namespace.

Hope this helps.
 
Leon said:
I need a program that generate 5 non-duplicates random number between 1-10
as string values store in an array.

Do anybody know of any good books or websites that explain how to generator
random numbers using asp.net? I know about the random namespace within .net,
but I need a reference to some code that do the similar stated function above.
Click to expand...

If you're really just after 5 out of 10, I'd suggest having an array of
10 booleans to say whether or not the number has always been picked, an
array of results, and just keep picking a new random number until
you've found one which hasn't been picked before, mark it as picked,
and add its string representation to the output array. Do that until
you've got 5 numbers, and you're done.

If that's not enough to go on, please give details of which bit you're
having trouble with.
 
Hi Jon,

I kind of understand what you are saying jon, but could please give me an
example?

Array of 10 booleans? you mean the random class would only search the number
that are false, if true it has been picked right?
Add its string representation to the output array? so I should have two
arrays one search and one store the picked values as strings
Do that until you've got 5 numbers? Loop until I have five non-duplicate
ramdon numbers?

Thanks!
 
Hi Leon,
I need a program that generate 5 non-duplicates random number between
1-10 as string values store in an array.
Click to expand...

For this you do *not* need a random number generator, because your number
*must not be* random!

Random-Number generators might produce duplicate numbers!

You can do something like this:

<code>
bool [] numbers = new bool[10];

Random r = new Random();
int hits = 0;
while(hits < 5)
{
int pos = r.Next(9);
if (numbers[pos] == true)
continue;
numbers[pos] = true;
hits++;
}

Console.WriteLine("Random-Numbers are: ");
for(int i=0; i<10; i++)
{
if (numbers == true)
Console.Write("{0} ", i.ToString());
}
Console.WriteLine();
</code>


--
Greetings
Jochen

My blog about Win32 and .NET
http://blog.kalmbachnet.de/
 
Leon said:
I kind of understand what you are saying jon, but could please give me an
example?

Array of 10 booleans? you mean the random class would only search the number
that are false, if true it has been picked right?
Yes.

Add its string representation to the output array? so I should have two
arrays one search and one store the picked values as strings
Do that until you've got 5 numbers? Loop until I have five non-duplicate
ramdon numbers?
Click to expand...

Basically, yes.

using System;

class Test
{
static void Main()
{
Random rng = new Random();

bool[] found = new bool[10];
string[] results = new string[5];

for (int i=0; i < results.Length; i++)
{
while (true)
{
int index = rng.Next(10);
if (!found[index])
{
found[index]=true;
results=index.ToString();
break;
}
}
}

foreach (string x in results)
{
Console.WriteLine (x);
}
}
}
 
Jochen Kalmbach said:
For this you do *not* need a random number generator, because your number
*must not be* random!
Click to expand...

On the contrary - he effectively first needs a random number between 0
and 9, then between 0 and 8, then between 0 and 7 etc.
Random-Number generators might produce duplicate numbers!
Click to expand...

So you have to apply it slightly differently. You still need a random
number generator though.
 
Hi Jochen,
Thanks for your response, but are you sure I don't need a random number
generator, because your code looks predictable.
the reason I need to use the random class is because I would like to feed
the program a seed ("such as time & ip address"), and the numbers may be
between 1 & 50, but the same solutions will apply.

Jochen Kalmbach said:
Hi Leon,
I need a program that generate 5 non-duplicates random number between
1-10 as string values store in an array.
Click to expand...

For this you do *not* need a random number generator, because your number
*must not be* random!

Random-Number generators might produce duplicate numbers!

You can do something like this:

<code>
bool [] numbers = new bool[10];

Random r = new Random();
int hits = 0;
while(hits < 5)
{
int pos = r.Next(9);
if (numbers[pos] == true)
continue;
numbers[pos] = true;
hits++;
}

Console.WriteLine("Random-Numbers are: ");
for(int i=0; i<10; i++)
{
if (numbers == true)
Console.Write("{0} ", i.ToString());
}
Console.WriteLine();
</code>


--
Greetings
Jochen

My blog about Win32 and .NET
http://blog.kalmbachnet.de/
Click to expand...
 
Hi Jon,
On the contrary - he effectively first needs a random number between 0
and 9, then between 0 and 8, then between 0 and 7 etc.
Click to expand...

No!
In your example, you presume that the first "random" number is 9, the
second is 8, ...!!!
To be correct you need to do the following:

R = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9} // set of numbers to choose from

a1 = random(R);

R1 = R without a1;
a2 = random(R1)

R2 = R1 without a2;
a3 = random(R2)

R3 = R2 without a3;
a4 = random(R3)

R4 = R3 without a4;
a5 = random(R4)


--
Greetings
Jochen

My blog about Win32 and .NET
http://blog.kalmbachnet.de/
 
<snip>

Note that that code produces 0-9, 1-10 - but it's a trivial tweak to
change the "base".
 
Leon said:
Thanks for your response, but are you sure I don't need a random number
generator, because your code looks predictable.
the reason I need to use the random class is because I would like to feed
the program a seed ("such as time & ip address"), and the numbers may be
between 1 & 50, but the same solutions will apply.
Click to expand...

The same solutions *don't* apply as the numbers get larger. That's why
I specified "If you're really after 5 out of 10" in my first post. The
same solutions are still feasible, but get more and more expensive.

For larger numbers, there are different approaches which could be used,
depending on whether the number of potential choices was much larger
than the number of results you want or whether they're close, etc. (For
instance, if you want nearly all the numbers, but in a random order, it
would be better to just pick the first n out of a random permutation.)
 
Hi Leon,
Thanks for your response, but are you sure I don't need a random
number generator, because your code looks predictable.
Click to expand...

Of course... you need a random number generator... but you have to handle
it a little bit different...

And my example is from the mathematical point of view, really bad!

See my other reply to Jon Skeet. Here I showed what really shoud be done...
(but at the moment I do not know who to implement it...)
The example from Jon is also very bad (as bad as mine).



--
Greetings
Jochen

My blog about Win32 and .NET
http://blog.kalmbachnet.de/
 
Jochen Kalmbach said:
No!
In your example, you presume that the first "random" number is 9, the
second is 8, ...!!!
Click to expand...

No I don't.

You seem to have assumed that I was just going to output the result of
the random number, which was never my intention at all.
To be correct you need to do the following:

R = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9} // set of numbers to choose from

a1 = random(R);

R1 = R without a1;
a2 = random(R1)

R2 = R1 without a2;
a3 = random(R2)

R3 = R2 without a3;
a4 = random(R3)

R4 = R3 without a4;
a5 = random(R4)
Click to expand...

Indeed - so on the first time, you need to pick one of ten numbers,
then one of nine, etc. That was what I was saying before.

You definitely *do* still need a random number generator (contrary to
your post), but you obviously can't just output the immediate result of
the call to the RNG.
 
Hi Jon Skeet [C# MVP],
No I don't.
Click to expand...

Maybe you just expressed it a little bit wrong:
<quote>
1. number between 0 and 9
2. number between 0 and 8
3. number between 0 and 7
and so on...
</quote>

But I am sure you meant:
1. select random number from 10 numbers
2. select random number from the remaining numbers
3. select random number from the remaining numbers
and so on...

You definitely *do* still need a random number generator
Click to expand...

Yes! It was a bit misleading...

--
Greetings
Jochen

My blog about Win32 and .NET
http://blog.kalmbachnet.de/
 
Jochen Kalmbach said:
Of course... you need a random number generator... but you have to handle
it a little bit different...
Click to expand...

Indeed, and I don't think anyone has disputed that. It was your claim
that you *didn't* need a random number generator that struck me as
highly odd.
And my example is from the mathematical point of view, really bad!

See my other reply to Jon Skeet. Here I showed what really shoud be done...
(but at the moment I do not know who to implement it...)
Click to expand...

Here's one potential way:

using System;

class Test
{
static Random rng = new Random();

static void Main()
{
Show (Permute (5, 10));
Show (Permute (5, 10));
Show (Permute (5, 10));
}

static void Show (int[] ints)
{
foreach (int i in ints)
{
Console.Write(i);
Console.Write(" ");
}
Console.WriteLine();
}

static int[] Permute (int length, int range)
{
int[] all = new int[range];
for (int i=0; i < all.Length; i++)
{
all = i;
}

for (int i=0; i < length; i++)
{
int index = i+rng.Next(range-i);
if (index != i)
{
int tmp = all;
all = all[index];
all[index] = tmp;
}
}

int[] result = new int[length];
Array.Copy (all, result, length);
return result;
}
}

It still takes as much space as the entire range, which may not be good
in some situations, but it's efficient in time. Basically it divides
the whole array, which initially contains all the values in order, into
the "chosen" section and "the rest", by swapping the non-chosen value
at any index with one of what's currently in "the rest" (allowing for
the possibility that the chosen value is the one at that index
already).

It would be nice to come up with a version which didn't have the space
constraint, but I can't easily think of anything which has neither
space nor time constraints.
The example from Jon is also very bad (as bad as mine).
Click to expand...

It's not bad for what was originally required - getting 5 numbers out
of 10. It's not as efficient as it might be, but for the task at hand
that shouldn't make a difference - and it's simpler than the above.
 
Jochen Kalmbach said:
Hi Jon Skeet [C# MVP],
No I don't.
Click to expand...

Maybe you just expressed it a little bit wrong:
<quote>
1. number between 0 and 9
2. number between 0 and 8
3. number between 0 and 7
and so on...
</quote>

But I am sure you meant:
1. select random number from 10 numbers
2. select random number from the remaining numbers
3. select random number from the remaining numbers
and so on...
Click to expand...

No, I meant a random number between 0 and 9. I didn't specify what was
then done with the number. You'll find that in another post, I do
exactly that - pick a number between 0 and 9, and then between 0 and 8.
I then use that number to find a number from the remaining ones.
 
Hi Jon,
No, I meant a random number between 0 and 9. I didn't specify what was
then done with the number.
Click to expand...

Ok, then I took the wrong assumption... sorry!
You'll find that in another post, I do
exactly that - pick a number between 0 and 9, and then between 0 and
8. I then use that number to find a number from the remaining ones.
Click to expand...

Ok, then I just missinterpreted it... sorry!

--
Greetings
Jochen

My blog about Win32 and .NET
http://blog.kalmbachnet.de/
 
Back
Top