Question

Write java program to check that a (16-digit) credit card number is valid. A valid credit card number will yield a result divisible by 10 when you:

Form the sum of all digits. Add to that sum every second digit, starting with the second digit from the right. Then add the number of digits in the second step that are greater than four. The result should be divisible by 10.

For example, consider the number 4012 8888 8888 1881. The sum of all digits is 89. The sum of the bold digits is 46. There are five bold digits larger than four, so the result is 140. 140 is divisible by 10 so the card number is valid.

• • Along the way, print out the step results:
    • sum of all digits
    • that result plus sum of every second digit
    • that result plus sum of every other digit greater than 4
    • divisible by 10 answer
• • print to the screen the original number & the final answer

Answer 1

CODE:

import java.util.Scanner;
public class Main
{
   public static void main(String[] args) {
  
Scanner sc = new Scanner(System.in);      
       System.out.println("Enter 16-digit credit card number: ");
      
       //inut of credit card number
       String str = sc.nextLine();
  
//calculating sum of digits      
       int sum_of_digits = 0;
       for(int i=0;i<str.length();i++){
       sum_of_digits += Integer.parseInt(str.charAt(i)+"");
       }
      
       //calculating sum of digits of odd places
       int sum_of_odd_place_digits = 0;
       for(int i=str.length()-2;i>=0;i-=2){
       sum_of_odd_place_digits += Integer.parseInt(str.charAt(i)+"");
       }
      
       //counting number of digits grater than 4 at odd places
       int count_of_odd_place_digits_greater_than_4 = 0;
       for(int i=str.length()-2;i>=0;i-=2){
       if(Integer.parseInt(str.charAt(i)+"") > 4)
       count_of_odd_place_digits_greater_than_4++;
       }
      
       //taking total sum
       int sum = sum_of_digits+sum_of_odd_place_digits+count_of_odd_place_digits_greater_than_4;
       System.out.println("sum of all digits : "+sum_of_digits);
      
       //printing desired details
       int sum_ = sum_of_digits+sum_of_odd_place_digits;
       System.out.println("result plus sum of every second digit : "+sum_);
       System.out.println("result plus sum of every other digit greater than 4 is : "+sum);
      
       if(sum%10 == 0){
       System.out.println("Valid credit card");
       }
       else{
       System.out.println("Invalid credit card");
       }
   }
}

SCREENSHOT:

OUTPUT: