Scratch

I'm no expert at Java, but I think it's because the "number++" line is inside the if block. Try moving it outside...? 

Otherwise, I think it'll never move past the first number that isn't prime. You still want to increment the variable "number", even if one of the numbers isn't a prime — does that make sense? 

ie, try:

public class primenumbers {
    public static void main (String[]args){
        int number = 3;
        int repeater;
        for (repeater = 1; repeater < 100; repeater++)/*repeat 100 times*/{
            int prime = 1;
            for(int divisor = 2; divisor < number; divisor++ ){
                if (number % divisor == 0){
                    prime = 0;
                    break;
                }
            }
            if (prime==1){
                System.out.println(number);
            }
            number++;
        }/*end for loop here*/   
    }    
}

(I tidied the code slightly, too; my apologies — I hope it still works...  )

Last edited by blob8108 (2011-12-16 07:58:11)

nXIII wrote:

You might also want to use the bool type instead of an int:

Code:

bool prime = true;
...
if (prime) {
    ...
}

(It won't break your code to do it with an int, but it's more semantically correct and sometimes takes up less space)

It's "boolean" in Java, not "bool".

boolean prime = true;
...

Last edited by ZeroLuck (2011-12-16 09:37:49)

blob8108 wrote:

I'm no expert at Java, but I think it's because the "number++" line is inside the if block. Try moving it outside...? 

Otherwise, I think it'll never move past the first number that isn't prime. You still want to increment the variable "number", even if one of the numbers isn't a prime — does that make sense? 

ie, try:

Code:

public class primenumbers {
    public static void main (String[]args){
        int number = 3;
        int repeater;
        for (repeater = 1; repeater < 100; repeater++)/*repeat 100 times*/{
            int prime = 1;
            for(int divisor = 2; divisor < number; divisor++ ){
                if (number % divisor == 0){
                    prime = 0;
                    break;
                }
            }
            if (prime==1){
                System.out.println(number);
            }
            number++;
        }/*end for loop here*/   
    }    
}

(I tidied the code slightly, too; my apologies — I hope it still works...  )

Still only prints 3 D:
i have no idea what's wrong.
*Extra useless info from advice dog.

More like advice fifth grader, cause I'm in fifth grade -_-

Last edited by matthew8092001 (2011-12-16 20:56:33)

well, i know how to do it in C++.

#include <iostream>

using namespace std

int main(){
 int const max_number (100);
 int const max_test (floor(sqrt(double(max_number)));
 bitset<max_number + 1> primes;
 primes.set();    //treat everything as prime until we know better
 primes[1] = 0 ;  //1 is not prime
 for (int i (1); i != max_test; ++i){
  if (primes[i]){  //if i is prime
   for (int j (i*i); j < max_test; j += i){  //eliminate multiples of i
    primes[j] = 0
  }
 }
 cout << "Here are a list of primes less than " << max_number << ": \n"
 for (int i (1); i != max_number + 1;  ++i){ //display results
  if (primes[i]){
   cout << primes[i] <<'\n'
  }
 }
}

Would it be possible to convert that to java?

MathWizz wrote:

This works for me:

Code:

public class primenumbers {
    public static void main(String[] args) {
        for (int number = 3; number < 100; number++)
            if (isPrime(number))
                System.out.println(number);
    }

    static boolean isPrime(int n) {
        boolean p = true;
        for (int i = 2; i < n; i++)
            if (n % i == 0)
                p = false;
        return p;
    }
}

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