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 11052012, 04:42 PM #1Member
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Identifying Prime Numbers from a Predefined Array
I'm taking a crash course in Java, and one of the assignments after the first day is to create a program that tells you all the prime numbers from a predefined array of numbers (we haven't gotten to scanners yet). I managed to write a program that works, but I've got a gut feeling that I did more than I should, and there's a simpler way. Can anyone guide me as to how (if possible) I can simplify this?
Java Code:public class TestPrime { public static void main(String[] args) { int[] numbers = new int[]{1,2,3,4,5,6,7,8,9,10}; boolean prime = true; for ( int i = 0 ; i < numbers.length ; i++){ switch (numbers[i]) { case 1: System.out.println(numbers[i] + " is a prime number"); break; case 2: System.out.println(numbers[i] + " is a prime number"); default: for (int x = 2 ; x < numbers[i] ; x++){ if (numbers[i]%x == 0){ prime = false; break; } if (prime = true) { System.out.println(numbers[i] + " is a prime number"); break; } } break; } } } }
xx is a prime number.
xx is a prime number.
xx is a prime number.
etc etc.
 11052012, 07:27 PM #2
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Re: Identifying Prime Numbers from a Predefined Array
That second ifstatement in the body of that last for loopstatement doesn't belong there (suppose 77 is an array element, it would be marked as being prime); move it after that loop and change 'prime = true' to 'prime == true'. Oh, and 1 isn't a prime number.
kind regards,
JosThe only person who got everything done by Friday was Robinson Crusoe.
 11062012, 01:40 AM #3Member
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Re: Identifying Prime Numbers from a Predefined Array
Thank you! I didn't realize that what I had before ended up showing me all the odds instead of the primes. But your suggestion along with moving the prime declaration to right after the "default;" line did it. Here's the latest version
Java Code:public class TestPrime { public static void main(String[] args) { int[] numbers = new int[]{17,23,53,123,66,3,2,1}; boolean prime; for ( int i = 0 ; i < numbers.length ; i++) { switch (numbers[i]) { case 1: System.out.println(numbers[i] + " is a prime number"); break; case 2: System.out.println(numbers[i] + " is a prime number"); break; default: prime = true; for (int x = 2 ; x < numbers[i] ; x++) { if (numbers[i]%x == 0) { prime = false; break; } else continue; } if (prime == true) { System.out.println(numbers[i] + " is a prime number"); break; } } } }
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