Re: Modulo Function - C# Discussion Boards

28-Aug-09 5:21

Hi,

Can someone tell me a MODULO algorithm like google's, typical calculator's, excel's, etc?

Because, they all return 0 for:
4029800 mod 100

But C# (and java I think) return -10

DaveyM6928-Aug-09 5:23

DaveyM69

28-Aug-09 5:23

4029800 % 100 gets 0 for me Confused | :confused:

Dave
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Visual Basic is not used by normal people so we're not covering it here. (Uncyclopedia)
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harold aptroot28-Aug-09 5:36

harold aptroot

28-Aug-09 5:36

Quake2Player wrote:

But C# (and java I think) return -10

Could you show the code? That really isn't what should happen, not in Java either.

Dave Kreskowiak28-Aug-09 7:15

Dave Kreskowiak

28-Aug-09 7:15

Your code is bad somewhere. For two positive integers, modulo is never negative.

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Dave Kreskowiak
Microsoft MVP
Visual Developer - Visual Basic
2006, 2007, 2008
But no longer in 2009...

Quake2Player28-Aug-09 7:22

28-Aug-09 7:22

Random r = new Random();

int key = r.Next(0, 10000);
int prime = r.Next(key, key * 999);
int a = r.Next(1, prime - 1);
int b = r.Next(0, prime - 1);

Console.WriteLine(key);
Console.WriteLine(prime);
Console.WriteLine(a);
Console.WriteLine(b);

Console.WriteLine( ((key*a + b)%prime) % 1000);
Console.ReadLine();

For example:
In google: (((8 568 * 4 974 445) + 2 820 002) % 7 661 773) % 1 000 = 563}
In c#: (((8 568 * 4 974 445) + 2 820 002) % 7 661 773) % 1 000 = -732

Luc Pattyn28-Aug-09 7:38

Luc Pattyn

28-Aug-09 7:38

Quake2Player wrote:
8 568 * 4 974 445)

using 32-bit signed arithmetic (as in int) this results in an overflow, that is where the negative stuff is coming from. Nothing wrong with the modulo operator.

test: declare long variables, initialize them, and use those for your expression, instead of numeric constants. (decimal should work too).

Smile | :)

Luc Pattyn

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DaveyM6928-Aug-09 7:38

DaveyM69

28-Aug-09 7:38

Beat me to it! Mad | :mad:

Quake2Player28-Aug-09 14:46

28-Aug-09 14:46

THANK YOU!

Re: Modulo Function [modified]

DaveyM6928-Aug-09 7:38

DaveyM69

28-Aug-09 7:38

It's because of the overflow in the first part of the calculation. Make one of the values a double and you get the correct result.
(((8568 * 4974445d) + 2820002) % 7661773) % 1000)

Quake2Player29-Aug-09 11:55

29-Aug-09 11:55

How can I use long if I'm generating random numbers???

This is all about the UNIVERSAL HASHING FUNCTION:

<code>
        public int Evaluate(int key) 
        {
                // Random prime bigger than 10000
                do {
                  randomPrime = rnd.Next(10001, 10000*999);
                }
                while (!IsPrime(randomPrime));

                this.randomA = rnd.Next(1, randomPrime - 1);
                this.randomB = rnd.Next(0, randomPrime - 1);

                return ((randomA * key + randomB) % randomPrime) % tableLength;
        }
</code>

Notes:
-10000 is the maximum possible key
-tableLength is 1000.
-randomA, randomB and randomPrime are ints

As Im getting negative numbers Im trying
return Math.Abs(((randomA * key + randomB) % randomPrime) % tableLength);

But its not giving me fast results in the hash table

modified on Saturday, August 29, 2009 6:01 PM

Using Text Files

gamer112728-Aug-09 4:54

gamer1127

28-Aug-09 4:54

Hello. I just want to know if its possible for me to store the data inside an array to a text file and also if its possible to transfer all the data in the text file into an array?

Coding C#28-Aug-09 4:55

Coding C#

28-Aug-09 4:55

Yes - Its possible Smile | :)

Coding C#

ExciteTemplate

gamer112728-Aug-09 5:13

gamer1127

28-Aug-09 5:13

Ok..Thanks.. Wink | ;)

OriginalGriff28-Aug-09 5:07

OriginalGriff

28-Aug-09 5:07

As Coding says, yes it is possible. How you do it will depend on what kind of info you have in your array, and what you want to do with the text file.

If it is an array of strings, easy peasy.
If it is an array of something else, then slightly harder - you will either have to do the work yourself or use a Formatter - XML, Binary or Soap.

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gamer112728-Aug-09 5:19

gamer1127

28-Aug-09 5:19

oh..ok then..thanks for the info..

OriginalGriff28-Aug-09 5:34

OriginalGriff

28-Aug-09 5:34

Sorry, that was a little unhelpfull!

For an array of strings, look at File.WriteAllLines[^]. To read it back, use ReadAllLines

For an array of something else, you will need to:
1) Open file
2) Set up a loop through each element of the array
3) For each element, use ToString member, or string.Format to create a string
4) Write the string to the file
5) Close the file.

To read them back, use the Parse method after reading the line.

or look at BinaryFormatter, XMLFormatter and SoapFormatter in the MSDN, but these will not necessarily create a file you want to look at, or edit by hand!

Good luck!

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Luc Pattyn28-Aug-09 7:40

Luc Pattyn

28-Aug-09 7:40

TMI
the first "yes" was the best answer Laugh | :laugh:

Luc Pattyn

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