### Thread: is number a prime number program

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#### is number a prime number program

I wrote this program to test whether or not a number is prime. I'm just starting out in programming, but when I look at this code, it seems there ought to be a simpler way to do it. Any ideas? (code works, I'm just looking for a better way to do it)

PHP Code:
``` import javax.swing.*; class Prime {     public static void main (String args[])     {         double prime = 0;      // this is the number that is tested (to see if it's prime)         double divisor = 0;    //          double counter = 1;    // this is the number I divide into prime         prime = Double.parseDouble(JOptionPane.showInputDialog("enter potential prime"));         while ( counter < ( prime / 2 ) )  // I only loop it through half of the posibilities because that's all that's necessary         {             if (prime % counter == 0)             {                 divisor = prime / counter;                 if (divisor != prime)                 {                     System.out.println(prime + " divided by " + counter + " equals " + divisor);                 }             }             counter += 1;         }         if (divisor == prime)         {             System.out.println(prime + " is prime");         }     System.exit(0);     } }  ```
Also, rather than supplying a number, I want it to list out all primes within a range. I tried nesting a while loop, and I didn't have much luck. Any thoughts on that aspect? thanks
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es5
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I don't program so you'll have to do the syntax...

You're close when you define this:

while ( counter < ( prime / 2 ) ) // I only loop it through half of the posibilities because that's all that's necessary

But, if a number is not prime, you will find a divisor by the time you reach the square root of the number.
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I'm using integers, so It will only return the square root if it's a perfect square