Java excercise - checking ID number

Question

I have a task with checking ID number and I must check if this ID has 11 characters, if those characters are digits and I must check control number. Number is correct when this equation is correct:

ID = abcdefghijk

(1*a+3*b+7*c+9*d+1*e+3*f+7*g+9*h+1*i+3*j+1*k) % 10 = 0

Sample correct ID is: 49040501580

And here is my program. I don't know how to check if ID is digit and why it isn't correct. Anyone help? XD Thank you in advance :3

import java.util.*;

public class wat {

    public static void main(String[] args) {
        char[] weights = {1, 3, 7, 9, 1, 3, 7, 9, 1, 3, 1};
        System.out.print("Enter next digits your ID number: ");
        Scanner keyboard = new Scanner(System.in);
        String number = keyboard.nextLine();
        char[] ofm = number.toCharArray();
        Character[] id = new Character[ofm.length];
        for (int i = 0; i < ofm.length; i++) {
            id[i] = ofm[i];
            System.out.print(id[i] + " ");
            int length = id.length;
            if (length == 11) {
                System.out.println("This ID number has 11 digits");
                System.out.println("Checking of the control number");
                int amount = 0;
                amount = id[i] * weights[i];
                System.out.println(amount);
                int result = 0;
                result = amount % 10;
                if (result == 0) {
                    System.out.println("ID number is correct");
                } else {
                    System.out.println("ID number is not correct");
                    break;
                }
            } else {
                System.out.print("This ID number hasn't 11 digits.");
                break;
            }
        }
    }

}

Sample output

Answer 1

With a minimal number of changes to your original code, I believe this is what you need.

import java.util.*;
     public class wat {
            public static void main(String[] args) {
                    char[] weights = {1,3,7,9,1,3,7,9,1,3,1};
                    System.out.print("Enter next digits your ID number: ");
                    Scanner keyboard = new Scanner(System.in);
                    String number = keyboard.nextLine();
                    char[] ofm=number.toCharArray();
                    Character[] id=new Character[ofm.length];
                    if (ofm.length == 11) {
                        System.out.println("This ID number has 11 characters");
                        int amount = 0;
                        for (int i = 0; i < ofm.length; i++) {
                                id[i]=ofm[i];
                                System.out.print(id[i]+" ");
                                int length = id.length;
                                if (isDigit(id[i])) {
                                        amount = id[i]*weights[i];
                                } else {
                                    System.out.println("character is not a digit");
                                    break;
                                }
                        }
                    } else {
                        System.out.print("This ID number hasn't 11 digits.");
                        return;
                    }
                    System.out.println("Checking of the control number");
                    System.out.println(amount);
                    int result =0;
                    result = amount % 10;
                    if (result == 0) {
                        System.out.println("ID number is correct");
                    } else {
                        System.out.println("ID number is not correct");
                    }
            }
    }

As you can see, we're now verifying the string length before the loop starts.

Then we're checking each character is a digit one by one and quitting with a new error message if one of them is not. You'll need to provide the isDigit function yourself (plenty to choose from on StackOverflow!).

We're accumulating the digit values multiplied by the weight into the amount variable, with a new value being added each time the loop iterates.

Finally we verify the result is correct after the loop has finished and all 11 characters have been processed.

NOTE: I don't normally work in Java so I'm not entirely sure if you can get the digit value out of a Character type object (to multiply it with the weight) like this. You might find that you are getting ASCII code values, or something else entirely. If this happens, you'll need to convert 'weights' into an array of integers, and extract the actual numeric value from the Character before multiplying them together.