[Solved] how can i determine all prime numbers smaller than a given input value? [duplicate]

Question

your code problem is int i = 0 start with 0 and next line if (N%i==0) so 10/0 is not possible throw a error something like java.lang.ArithmeticException: / by zero is not possible

and you loop through result.length, you need to loop through i your parent loop and put condition inside if (N%i==0) and you need many changes saw my below answer and debug where you get unexpected output and follow.

brute Force

public static void main(String[] args) {
        int N = 50;
        List<Integer> result = new ArrayList<>();
        for (int i = 1; i < N; i++) {
            boolean isPrime = true;
            for (int j = 2; j < i - 1; j++) {
                if (i % j == 0) {
                    isPrime = false;
                    break;
                }
            }
            if (isPrime) {
                result.add(i);
            }
        }
        result.forEach(System.out::println);

    }

optimize one using Math.sqrt reason

public static void main(String[] args) {
        int N = 101;
        List<Integer> result = new ArrayList<>();
        for (int i = 1; i <= N; i++) {
            boolean isPrime = true;
            for (int j = 2; j < Math.sqrt(i - 1); j++) {
                if (i % j == 0) {
                    isPrime = false;
                    break;
                }
            }
            if (isPrime) {
                result.add(i);
            }
        }
        result.forEach(System.out::println);
}

using BigInteger.isProbablePrime see

public static void main(String[] args) {
        int N = 101;
        List<Integer> result = new ArrayList<>();

        for (long i = 1; i <= N; i++) {
            BigInteger integer = BigInteger.valueOf(i);
            if (integer.isProbablePrime(1)) {
                result.add((int) i);
            }
        }
        result.forEach(System.out::println);

    }

Updated 1:- that something you want

try (Scanner scanner = new Scanner(new File(args[0]))) {
            int N = Integer.parseInt(scanner.nextLine());
            int[] result = new int[N];
            int resultIncreamenter = 0;
            // here for loop logic can be replaced with above 3 logic
            for (int i = 1; i <= N; i++) {
                boolean isPrime = true;
                for (int j = 2; j < Math.sqrt(i - 1); j++) {
                    if (i % j == 0) {
                        isPrime = false;
                        break;
                    }
                }
                if (isPrime) {
                    result[resultIncreamenter++] = i;
                }
            }
            for (int j = 0; j < result.length; j++) {
                System.out.print(result[j]);
                if (j < result.length - 1) {
                    System.out.print(" ");
                }
            }
            System.out.println();
        } catch (FileNotFoundException ex) {
            throw new RuntimeException(ex);
        }

Accepted Answer