random numbers

Hi x_3fPSta

I have another program that I have written that generates random numbers from1 to 20. There is a pressing enter key to continue.

Also the choices are y for yes and n for no. This program is similar to the other program for choicing random numbers between 1 and 3.

Here is the program code:

// PickRandomNumbers.java

// PickRandomNumbers uses random to pick numbers from 1 to 20.

import java.util.Random;// program uses class Random

import java.util.Scanner; // program uses class Scanner

public class PickRandomNumbers

{

// main method begins program execution

public static void main( String args[] )

{

Random randomNumbers = new Random();

int startRandomNumbers = 1;// this is the starting position for where the

// random numbers start to generate

int maxRandomNumber = 20;// this is the max random number

Scanner input1 = new Scanner(System.in);

Scanner input2 = new Scanner(System.in);

String theInput;

boolean wantContinue;// for the do while loop condition for checking choice

char choice;// y for yes or n for no choice

do // this do while loop randomly chooses a number from 1 to 20

{

int chooseRandomNumber = startRandomNumbers + randomNumbers.nextInt(maxRandomNumber);

System.out.printf("\n%s%d\n\n","The random number is ",chooseRandomNumber);

System.out.println("Press Enter to continue ...");

input1.useDelimiter("\n");

String garbage = input1.next();

System.out.println();

do // this do while loop test if the choice is either y or n or other character

{

System.out.printf("Do you want to continue? y for yes , n for no : ");

theInput = input2.next();

choice = theInput.charAt(0);

if (choice == 'y' || choice == 'Y' || choice == 'n' || choice == 'N')

wantContinue = false;

else // if choice is other than y or n

wantContinue = true;

}

while (wantContinue != false);

}

while (choice == 'y' || choice == 'Y');

} // end main

} // end class PickRandomNumbers

egan128a at 2007-7-14 21:28:13 >

> I have another program that I have written that

> generates random numbers from1 to 20. There is a

> pressing enter key to continue.

> Also the choices are y for yes and n for no. This

> program is similar to the other program for choicing

> random numbers between 1 and 3.

egan128: You shouldn't call the maxRandomNumber the "max". Try setting your "startRandomNumber" to 5 and your so-called "maxRandomNumber" to 20. Your range will not be "5 to 20".

MLRona at 2007-7-14 21:28:13 >

Hi,

Since this is a newby corner of the forum, and I am a newby, and I actually didn't understand what all these people are talking about, and I know a simple answer ... :)

There is something that is called Math.random()

that generates a random "double" number from 0 to 0.99999....

So if you for example wish to have the numbers 1 to 3 then you need to multiply that random number like this Math.random()*3

.

Now you have a "double" random number from 0 to 2.9999...

To get the number 1 to 3, you now need to add 1 (Math.random()*3)+1

.

Now you have a random number from 1 to 3.999...

But you want an integer, and not a double. You fix it like this (int)((Math.random()*3)+1)

So you should write in your code:

int randomNumber = (int)((Math.random()*3)+1);

Works every time, guaranteed! Have fun programming! Greetz, Daffn.

Daffna at 2007-7-14 21:28:13 >

> > and I know a simple answer

>

> A swing and a miss! ; )

>

> java.util.Random random = new java.util.Random();

> int number = random.nextInt(3);

>

> will give an int 0,1,2

>

> http://java.sun.com/j2se/1.4.2/docs/api/java/util/Rand

> om.html

Why?

int randNum = (int)(Math.random() * 3 + 1);

That will give him a random number between 1 and 3.

CaptainMorgan08a at 2007-7-14 21:28:13 >

> There is something that is called

> Math.random()

that generates a random

> "double" number from 0 to 0.99999....

Yes.

That is well known, and is not the best solution here.

> So if you for example wish to have the numbers 1 to 3

> then you need to multiply that random number like

> this Math.random()*3

.

> Now you have a "double" random number from 0 to

> 2.9999...

> To get the number 1 to 3, you now need to add 1

> (Math.random()*3)+1

.

That's not as good as the use of java.util.Random.nextInt(int n). The reasons are well documented, but i don't have them handy right now. Google for java random or something.

> Works every time, guaranteed! Have fun programming!

> Greetz, Daffn.

No. It's harder to read and produces inferior results. See above.

jverda at 2007-7-21 10:13:10 >

Eum, it's me agian, why "swing and miss"? It works you know, and your way is good too, but look at the original post. He asks a number form 1 to 3 and not from 0 to 2.

Quote CaptainMorgan08:

Why?int randNum = (int)(Math.random() * 3 + 1);

That will give him a random number between 1 and 3.

End Quote.

Well, why? Simple, cos he asks for 1,2,3 and not 0,1,2

So, the best 2 ways so far for solving this problem:

int randNum = (int)(Math.random() * 3 + 1);

and

int number = (random.nextInt(3) + 1);

Daffna at 2007-7-21 10:13:10 >

int[] choices = { 0, 2, 3 };

java.util.Random rand = new java.util.Random();

int index = rand.nextInt(choices.length);

int yourRandomNumber = choices[index];

[EDIT] I'm a bit slow this morning. No surprise, really. :o)

yawmarka at 2007-7-21 10:13:10 >

> the generator seems to give me numbers that are very close alot of the times.

Did you know that if you put 23 people in a room, there's a greater than 50% chance that two of them have the same birthday?

> so i was wondering if math.random was any better than Random.

The Math.random() method delegates to an instance of java.util.Random, if I recall correctly.

~

yawmarka at 2007-7-21 10:13:10 >

> No need to post code, i know its not

> wrong

Famous last words. "My code can't be wrong. It must be the tool."

Regardless of how correct you think your code is, if you won't post the code and details of what it's doing--actual numbers as well as "the squares are about the same size," then there's no way for anybody to help you. I can say with high degree of confidence, however, that just switching to Math.random won't help.

jverda at 2007-7-21 10:13:14 >

It is possible to make a pseudo-random number number generator which misses out number, which is terribly biased or which repeats after just a few iterations, or all three. In fact it's pretty easy to write such a thing if you're doing it badly. That's why random number generators are a special interest for casual programmers, cryptography experts and hackers.

You don't need anything nearly as elaborate as a device which measures radiactive decay or background radiation from deep space to get natural random numbers. You can make such a thing with an analogue feedback circuit which generates electrical noise and then convert it to digital.

vapourmilea at 2007-7-21 10:13:15 >