Primality Test

[Jason Marceau]

Hi,

I have to write a program that tests if a number entered is prime or not.

I have finished all the code to display input prompts and output message

Example: " Enter a number: " - " x is a prime number" - " x is not a prime number" etc

Does anyone know how to write the code to test if a number is prime or not?

I think I would have to divide the input number and check if it is equal to 0. If it is equal to 0 it would not be prime.

Something like this:

division = 2;

input / division

If( division == 0)
System.out.println( result + " is not a prime number");

I'm not sure.

Appreciate any help with this.

Thank you

[nanosani]

See if this function works :

public void calculatePrime(int number){
   for( int i = 2; i < number i++){
      if((number % i) == 0){
         System.out.println("The number you entered is not a prime");
         return;
      }
   }
   System.out.println("The number you entered is prime");
}

[Jason Marceau]

See if this function works :

public void calculatePrime(int number){
   for( int i = 2; i < number i++){
      if((number % i) == 0){
         System.out.println("The number you entered is not a prime");
         return;
      }
   }
   System.out.println("The number you entered is prime");
}

Thank you very much, I will write it in with my code tonight and see how it goes, Thank you!!!!!!!!!!!

You are a great help!!!!!!!

[nanosani]

Your code looks like all conjusted ... I've tried to read it but you should check for the opening and closing brackets ... your if statement was not in the for loop.

import java.io.*;

public class PrimalityTest
{

   public static void main(String[] args)throws IOException
   {


   // create a keyboard input stream
   BufferedReader stdin = new BufferedReader (new
   InputStreamReader(System.in));

   // variables to store input
   int Input;



   do
   {

      // prompt for user input
      System.out.print("Please enter a number: ");
      Input = Integer.parseInt(stdin.readLine());

      // test for prime number

      for (int i = 2; i < Input; i++)
      {
      // your code help
         if ((Input % i) == 0)
         {
            System.out.println(Input + " is not a prime number"); // here is the non  working loop, it stops here when the number is not prime
            return;
         }

      }
   }
   while (Input !=0);
   }  
}

[jerbo]

The clue is in the 'return'.

Maybe you meen to do something else?

[nanosani]

May be you could use break instead of return.... I had written the method seperately and you merged it into the main method.

import java.io.*;

public class PrimalityTest
{

   public static void main(String[] args)throws IOException
   {


   // create a keyboard input stream
   BufferedReader stdin = new BufferedReader (new
   InputStreamReader(System.in));

   // variables to store input
   int Input;



   do
   {

      // prompt for user input
      System.out.print("Please enter a number: ");
      Input = Integer.parseInt(stdin.readLine());

      // test for prime number

      for (int i = 2; i < Input; i++)
      {
      // your code help
         if ((Input % i) == 0)
         {
            System.out.println(Input + " is not a prime number"); // here is the non  working loop, it stops here when the number is not prime
            break;
         }

      }
   }
   while (Input !=0);
   }  
}