Code printing out lines twice within while loop?

Question

In this code the user types in a test mark and that it should print out the grade and ask whether or not the user would like to enter another mark, however, my problem is that it prints out this bit twice and I don't know why?

import java.util.Scanner;

public class ExamGrades {

    public static void main(String[] args) {
        int mark;
        String answer;
        Scanner scan = new Scanner(System.in);

        System.out.println("Enter student mark: ");
        mark = scan.nextInt();
        while (mark >= 0) {

            if (mark < 40) {
                System.out.println("FAILED.");
            } else if (40 <= mark && mark <= 49) {
                System.out.println("3rd");
            } else if (50 <= mark && mark <= 59) {
                System.out.println("2/2");
            } else if (60 <= mark && mark <= 69) {
                System.out.println("2/1");
            } else if (mark >= 70 && mark <= 100) {
                System.out.println("1st");
            } else if (mark > 100) {
                System.out.println("Invalid mark");
            }

            System.out.println("Enter another mark? Yes or No: ");
            answer = scan.nextLine();

            if (answer.equalsIgnoreCase("yes")) {
                System.out.println("Enter student mark: ");
                mark = scan.nextInt();
            } else if (answer.equalsIgnoreCase("no")) {
                mark = -1;
                System.out.println("Thank you.");
            }

        }
        scan.close();
    }
}

Thank you for any help you can give.

Answer 1

Reason is when you enter the marks, you press say 56<enter>. Your API nextInt just reads 56 and leaves enter which gets consumed by nextLine api.

Inorder to avoid this, just before your sysout below:

System.out.println("Enter another mark? Yes or No: ");

Type the following line:

scan.nextLine();

So that your <enter> gets consumed by this api and you can successfully move forward reading user input Yes/No.