September 16th, 2013, 01:58 PM

Need a little help
Hello, I wonder if you could help me fixing my java code, which's supposed count prime numbers. The code is as follws:
[/public class PrimeNumber
{ public static void main(String[] args)
{ int N = Integer.parseInt(args[0]); int count= 0;
for(int i=1; i < N; i++)
{
boolean prime = true;
if (i == 2)
count++;
else if (i % 2 == 0 && i != 2)
prime=false;
else if(i == 1)
prime=false;
for(int j=3; j*j <=N && prime == true; j+=2)//j er <=SQRT(N)
{
if (i % j == 0) prime = false;
}
if (prime == true  i == 2) count++;
}
System.out.println(count);
}
}]
Thanks in advance.
It's supposed to count how many numbers of a given input are prime numbers, but I don't get the right result
September 16th, 2013, 02:46 PM

Please edit the post and wrap the code in code tags:
[code]
>>>>>CODE HERE
[/code]
Can you explain what the code does now and what you want it to do differently.
September 16th, 2013, 02:58 PM

Originally Posted by NormR
Please edit the post and wrap the code in code tags:
[code]
>>>>>CODE HERE
[/code]
Can you explain what the code does now and what you want it to do differently.
I've added it now
September 16th, 2013, 03:56 PM

What did you add and where did you add it? I don't see any difference in the code in your post.
It should look like this:
Code:
private double dotProduct(double[] pointA, double[] pointB, double[] pointC)
{
double[] AB = new double[2];
double[] BC = new double[2];
AB[0] = pointB[0]  pointA[0];
AB[1] = pointB[1]  pointA[1];
BC[0] = pointC[0]  pointB[0];
BC[1] = pointC[1]  pointB[1];
double dot = AB[0] * BC[0] + AB[1] * BC[1];
return dot;
}
I don't get the right result
Please explain. Show current result and desired output.
Last edited by NormR; September 16th, 2013 at 03:59 PM.
September 17th, 2013, 09:11 AM

Here is the working code. It had to be modified a lot, I suppose. But, your base code was still used so that you can follow along:
Code:
public class PrimeNumber
{
public static void main(String[] args)
{
if(args.length == 0)
{
System.out.println("Please provide a numeric input argument.");
System.exit(0);
}
int N = Integer.parseInt(args[0]);
int count= 0;
boolean prime;
System.out.println("Now printing prime numbers between 0 and " + N);
if(N > 1)
{
System.out.print("2, "); // 2 will always be prime.
count++;
}
for(int i=3; i < N; i+=2) // Only check odd numbers
{
prime = true; // Success flag
for(int j=3; j <= N ; j++)
{
if (i % j == 0 && i != j)
{ // Number is divisible by other than 1 or itself
prime = false; // This is not prime; so, no need to check any more
// for this 'i' number.
break; // break out of inner for loop
}
} // end inner for loop
if(prime == true)
{
System.out.print(i + ", ");
count++;
}
} // end outer for loop
System.out.println("\n" + count + " primes found.");
} // end main()
} // end class
Here is the output:
Code:
prompt%> java PrimeNumber 100
Now printing prime numbers between 0 and 100
2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97,
25 primes found.
Regards  Shawn  robowhiz.info
Comments on this post