Java Programs - Solved 2025 Theory Paper ISC Computer Science

import java.util.Scanner;
class Perni{
    int num;
    public Perni(){
        num = 0;
    }
    public void accept(){
        Scanner in = new Scanner(System.in);
        System.out.print("Enter a binary number: ");
        num = Integer.parseInt(in.nextLine());
        String s = String.valueOf(num);
        s = s.replace("0", "");
        s = s.replace("1", "");
        if(s.length() != 0){
            System.out.println("Invalid binary number!");
            System.exit(0);
        }
    }
    public int countOne(int k){
        if(k == 0)
            return 0;
        int d = k % 10;
        if(d == 1)
            return 1 + countOne(k / 10);
        return countOne(k / 10);
    }
    public void check(){
        int count = countOne(num);
        int f = 0;
        for(int i = 1; i <= count; i++){
            if(count % i == 0)
                f++;
        }
        if(f == 2)
            System.out.println(num + " is a pernicious number!");
        else
            System.out.println(num + " is not a pernicious number.");
    }
    public static void main(String[] args){
        Perni obj = new Perni();
        obj.accept();
        obj.check();
    }
}