How to create a random number without an 8 & 9?
Hi I am trying to make random phone numbers but for the area code I don't want any 8 or 9. How can I do it?
Here is my code:
publicstaticvoid main(String[]args)
{
//declaration section
Random generator =new Random();
int areacode,num1, num2;
//generate phone digits
areacode= generator.nextInt(700);//areacode it can't have an 8 or 9
num1= generator.nextInt(643)+ 100;//second set
num2= generator.nextInt(9000)+ 1000;//third set
//Decimal Format
DecimalFormat fmt =new DecimalFormat ("#000");
System.out.print("Phone Number:" + fmt.format(areacode)+"-" + num1 +"-" + num2);
}
}
[1254 byte] By [
Bijou03a] at [2007-10-3 6:32:40]
A math guru like Jos might have a better way but you could write a method.
private int getAreaCode(limit) {
while true {
generate number
if number doesn't contain an 8 or a 9
return number
}
}
}
> Help please...In future do you think you can wait more than 10 minutes before whining?
Is there another way of doing this?
Yes. In programming there are plenty of ways to achieve the same result. Care to explain what is so bad about my solution.
I don't like the idea of discarding attempts with the wrong digits and then trying again, because there is a small but finite probability that the loop will never end.
I would do it by generating random ints from 0-7 three times and adding that to the total, multiplying by ten each time to put them in the right position.
yes I will generate each separately....
Or even better append them to a StringBuffer.
thanks for your help but I still haven't learn how to use StringBuffer.
If you haven't been told you can't use it then learn it now. I'm sure the teacher won't mark you down if you do.
java.util Class Random int nextInt(int n) Returns a pseudorandom, uniformly distributed int value between 0 (inclusive) and the specified value (exclusive), drawn from this random number generator's sequence.
>> I don't like the idea of discarding attempts with the wrong digits and then trying again, because there is a small but finite probability that the loop will never end.
Thats not true. Computer random isnt real random - meaning, a number without an 8 or 9 WILL come up eventually.
In real random you can be flipping a coin and get heads for the rest of your life - that wont happen with computer random.
This may not be a perfect solution but:
int answer;
int[] valid = {0, 1, 2, 3, 4, 5, 6, 7}
for(int i = digitCount: i > 0; i--){
int random = Random.nextInt(8);
int digit = valid[random];
answer += (random * pow(10, i))
}
woops, because you are excluding 8 and 9 (which are at the end) you dont need the valid array.That would work well though for cases where you were excluding say 2 and 6 or something.
> Thats not true. Computer random isnt real random -
> meaning, a number without an 8 or 9 WILL come up
> eventually.
But that depends on how the random number generator is implemented. It may be true in Java now, but I certainly wouldn't want to write any code that depended on that fact. And even if you could be certain that all numbers would come up eventually no matter what, it might be only after an unacceptably long time in the worst case.
>> it might be only after an unacceptably long time in the worst case.
agreed. i can see it taking too long to cycle.
>> But that depends on how the random number generator is implemented.
not to argue because this really isnt in my body of knowledge but
isnt ANY rand#gen - and at least java's - attempting to be evenly
distributed?
i think i can argue that it wouldnt be if it were possible to cycle
without getting a number with an 8 or 9 in it. : )
Why can't the area code have an 8 or a 9? Your phone numbers are in the format of U.S. phone numbers, and real U.S. area codes have both.
non-business numbers?> Why can't the area code have an 8 or a 9? Your phone> numbers are in the format of U.S. phone numbers, and> real U.S. area codes have both.
> non-business numbers?
> > Why can't the area code have an 8 or a 9? Your
> phone
> > numbers are in the format of U.S. phone numbers,
> and
> > real U.S. area codes have both.
Yes:
Area Code, Region, Timezone Offset from UTC, Description
949 CA -8 California: S Coastal Orange County
818 CA -8 S California: Los Angeles: San Fernando Valley
786 FL -5 SE Florida, Monroe County
682 TX -6 Texas: Fort Worth areas
And many others:
http://www.cs.ucsd.edu/users/bsy/area.html
>> http://www.cs.ucsd.edu/users/bsy/area.html Haha...Without 8 or 9 who would call upper central Michigan!!!989MI -5 Upper central Michigan: Mt Pleasant, Saginaw
> not to argue because this really isnt in my body of
> knowledge but
> isnt ANY rand#gen - and at least java's - attempting
> to be evenly
> distributed?
> i think i can argue that it wouldnt be if it were
> possible to cycle
> without getting a number with an 8 or 9 in it. : )
That's probably true of any psuedo-random number generator, but it's not hard to get what should be a truly random number by measuring something physical, like the noise of a resistor on the motherboard (random enough that you could theoretically go all day without seeing a given number, anyway). I don't think any normal computers have such a feature as standard today, but it might be common tomorrow.
So you're probably right that it's not a problem that would crop up now, but it seems like a good idea to think ahead (don't want any Y2K-type problems cropping up!).
> but it's not hard to get what should be a truly random number by
> measuring something physical, like the noise of a resistor on the
> motherboard
Alan Turing apparently built physically indeterminate hardware into his
machines, and considered this part of "computing". Or at least so I
remember reading - historians of the art will no doubt correct me if I'm
wrong.
I have seen commercial cards for sale on trhe Internet which
provide sources of random bits at a good bandwidth provided by
radioactive sources. (No mention of whether they keep your coffee
warm as well.) And a web site - googled it, it's here:
http://www.fourmilab.ch/hotbits/hardware.html - offers online hot bits
at the modest rate of 100bps. The hippies at www.random.org
use atmospheric noise.
Is there really any difference between these sources of the (scientists
believe) physically indeterminate behaviour and the likes of say
Math.random()?
If you think so, I hope you'll behave nicely towards the next poster
who wants the "correct" answer to their floating point problems.
You could generate *any* integral random number, convert it to itsoctal string representation and convert it back to an int again as if itwere a decimal representation of a number.kind regards,Jos
JosAHa at 2007-7-21 11:34:32 >
edit: This one was ****. Forget it.
