Loop issue

[apollo abel]

Ok, i've been trying since like 2 days ago to solve this problem, but i havent been able to do so.
this is the error i get:

what is your name: neo
Hello neo Do you want to go first? (1)Yes, (2)No
1
the number of marbles is: 42
How many marbles you want to remove? 60
the number of marbles left is -18
It is now the computer's turn
Exception in thread "main" java.lang.IllegalArgumentException: n must be positiv
e
        at java.util.Random.nextInt(Random.java:248)
        at GameTester.main(GameTester.java:61)
Press any key to continue...

As you can see the game ends when i enter a number higher than the number of marbles. however, i dont want the game to end, i want it ask the question again, until the user enters a number thats is not greater than the number of marbles, and that is not greater than the number of marbles divided by 2.
this is the code i have so far, i've tried making a boolean method but it always escape the program, i want it to repeat the question:

System.out.print("How many marbles you want to remove? ");

this is the code i have so far:

import java.util.Random;
public class Game
{
private String name;
private String answer;
private int numMarbles;
private int marblesTaken;
private int pcMarblesTaken;
int goodData;

public Game(String name)
{
this.name = name;



}

public String getName()
{
return name;
}

public boolean getGoodData()
{
//if(marblesTaken >= numMarbles || marblesTaken < 1 || marblesTaken > (numMarbles/2))

//return true;
if((marblesTaken > 1) && (marblesTaken <= (numMarbles/2)))

return true;
return false;





}

public int getNum()
{
return marblesTaken;
}

 
}

import java.util.Random;
import java.util.Scanner;
public class GameTester
{
public static void main (String [] args)
{

Scanner input = new Scanner(System.in);
String exit = "1";

do
{


System.out.print("what is your name: ");
String name = input.next();

Game howdy = new Game(name);
String aString = "1";
do
{


System.out.println("Hello " + howdy.getName() + " Do you want to go first? (1)Yes, (2)No");
aString = input.next();


}
while(!aString.equals("1") && !aString.equals("2"));



if(aString.equalsIgnoreCase("1"))
{

Random random = new Random();
int min = 10;
int max = 100;
int diff = max - min + 1;
int numMarbles = random.nextInt(diff) + min;

System.out.println("the number of marbles is: " + numMarbles);


while(numMarbles > 1)
{

do
{
System.out.print("How many marbles you want to remove? ");
int marblesTaken = input.nextInt();

numMarbles = numMarbles - marblesTaken;
}
while(howdy.getGoodData());

System.out.println("the number of marbles left is " + numMarbles);

System.out.println("It is now the computer's turn");

int pcMarblesTaken = random.nextInt(numMarbles/2)+1;

System.out.println("the computer has taken " + pcMarblesTaken + " marbles");

numMarbles = numMarbles - pcMarblesTaken;

System.out.println("the number of marbles left is: " + numMarbles);


if (numMarbles==1)
{
System.out.println(howdy.getName()+ " You lose");
break;
}
 
System.out.println("It is now your turn");

}


}
else
{
Random random = new Random();
int min = 10;
int max = 100;
int diff = max - min + 1;
int numMarbles = random.nextInt(diff) + min;

System.out.println("the number of marbles is: " + numMarbles);

while(numMarbles > 1)
{
int pcMarblesTaken = random.nextInt(numMarbles/2)+1;

System.out.println("the computer has taken " + pcMarblesTaken + " marbles");

numMarbles = numMarbles - pcMarblesTaken;

System.out.println("the number of marbles left is: " + numMarbles);

System.out.println("It is now your turn");

System.out.print("How many marbles you want to remove? ");
int marblesTaken = input.nextInt();

numMarbles = numMarbles - marblesTaken;

System.out.println("the number of marbles left is " + numMarbles);


if (numMarbles==1)
{
System.out.println(howdy.getName()+" You Win!!");
break;
}

System.out.println("It is now the computer's turn");

}

}

do
{

System.out.print("Do you want to play again? (1)Yes, (2)No ");
exit = input.next();
}
while(!exit.equals("1") && !exit.equals("2"));
if(exit.equals("2"))
{
System.out.println("Thanks for playing with us!");
break;
}
}
while(exit.equals("1"));


}

}

thanks for the support
[ April 01, 2006: Message edited by: apollo abel ]

[Paul Santa Maria]

To prevent the exception, you need something like this:

int numMarbles;
  if (diff > 0)
    numMarbles = random.nextInt(diff) + min;
  ...

But the real problem is that you probably want to constrain numMarbles to some number between min and the number of marbles actually left. For example:

  ...
  numMarbles = numMarbles - pcMarblesTaken;
  pcMarblesTaken = min + (Math.abs(random.nextInt()) % (numMarbles - 1)) ;
  ...

As far as exiting the loop - I confess I haven't looked carefully at your code. It can definitely be simplified ... but as far as I can tell, once you compute the random value and pcMarblesTaken correctly, then it looks like numMarbles should eventually go down to zero and the loop exit. So you should be OK...

'Hope that helps .. PSM
[ April 01, 2006: Message edited by: Paul Santa Maria ]

[apollo abel]

Ok, the code now its done - well not really, is not an efficient code -
here it is:

import java.util.Random;
public class Game
{
private String name;
private String answer;
private int numMarbles;
private int marblesTaken;
private int pcMarblesTaken;
private int goodData;

public Game(String name)
{
this.name = name;

}

public void setMarbleCount(int numMarbles)
{
this.numMarbles = numMarbles;
}

public String getName()
{
return name;
}

public void takeMarbles(int marbles)
{
    marblesTaken = marbles;
}
 
public void updateMarbleCount()
{
    numMarbles = numMarbles - marblesTaken;
}

public boolean getGoodData()
{
if((marblesTaken > 0) && (marblesTaken <= (numMarbles/2)))

return true;
return false;
}

public int getNum()
{
return marblesTaken;
}

public int getMarbles()
{
return numMarbles;
}
 
}

import java.util.Random;
import java.util.Scanner;
public class GameTester
{
public static void main (String [] args)
{

Scanner input = new Scanner(System.in);
String exit = "1";

do
{


System.out.print("what is your name: ");
String name = input.next();

Game howdy = new Game(name);
String aString = "1";
do
{


System.out.println("Hello " + howdy.getName() + " Do you want to go first? (1)Yes, (2)No");
aString = input.next();


}
while(!aString.equals("1") && !aString.equals("2"));



if(aString.equalsIgnoreCase("1"))
{

Random random = new Random();
int min = 10;
int max = 100;
int diff = max - min + 1;
int numMarbles = random.nextInt(diff) + min;
howdy.setMarbleCount(numMarbles);

System.out.println("the number of marbles is: " + numMarbles);


while(howdy.getMarbles() > 1)
{

do
{
    System.out.print("How many marbles you want to remove? ");
    howdy.takeMarbles(input.nextInt());
} 
while(!howdy.getGoodData());
howdy.updateMarbleCount();
 


System.out.println("the number of marbles left is " + howdy.getMarbles());

System.out.println("It is now the computer's turn");

int pcMarblesTaken = random.nextInt(howdy.getMarbles()/2)+1;

System.out.println("the computer has taken " + pcMarblesTaken + " marbles");

howdy.setMarbleCount(howdy.getMarbles() - pcMarblesTaken);
 


System.out.println("the number of marbles left is: " + howdy.getMarbles());


if (howdy.getMarbles()==1)
{
System.out.println(howdy.getName()+ " You lose");
break;
}
 
System.out.println("It is now your turn");

}


}
else
{
Random random = new Random();
int min = 10;
int max = 100;
int diff = max - min + 1;
int numMarbles = random.nextInt(diff) + min;
howdy.setMarbleCount(numMarbles);

System.out.println("the number of marbles is: " + howdy.getMarbles());

while(howdy.getMarbles() > 0)
{
int pcMarblesTaken = random.nextInt(howdy.getMarbles()/2)+1;

System.out.println("the computer has taken " + pcMarblesTaken + " marbles");

howdy.setMarbleCount(howdy.getMarbles() - pcMarblesTaken);
 

 


System.out.println("the number of marbles left is: " + howdy.getMarbles());

System.out.println("It is now your turn");

do
{
    System.out.print("How many marbles you want to remove? ");
    howdy.takeMarbles(input.nextInt());
} 
while(!howdy.getGoodData());
howdy.updateMarbleCount();



System.out.println("the number of marbles left is " + howdy.getMarbles());


if (howdy.getMarbles()==1)
{
System.out.println(howdy.getName()+" You Win!!");
break;
}

System.out.println("It is now the computer's turn");

}

}

do
{

System.out.print("Do you want to play again? (1)Yes, (2)No ");
exit = input.next();
}
while(!exit.equals("1") && !exit.equals("2"));
if(exit.equals("2"))
{
System.out.println("Thanks for playing with us!");
break;
}
}
while(exit.equals("1"));


}

}