Why is this Java code not working calculate average max and min?

Question

I am supposed to build a program that gets the grades in a class and calculates min and max and average then ask if you want to continue. This is the code I used but it's still not working. Can you see where the mistake is?

public class calculateAvgMAxMin
{
    public static void main(String[] args)
    {
        Scanner input = new Scanner(System.in); // declares scanner input
        LinkedList<Integer> list = new LinkedList<Integer>(); // declare new LinkedList of variables which are the grades

        int answer = 1; // declare variable answer =1 
        do { // start of do loop 

            System.out.print("Please enter the name of the course:"); // gives a prompt to enter the name of the course

            // goes to the next line

            String course=input.nextLine(); // declare course as string and sets the value as the input

            System.out.println("Please enter the scores for " + course + " on a single line and type a -1 at the end"); //prompts user to enter scores for class in one line and -1 to stop

            int max=-100; // declare max as integer = -100
            int min=500;//declare min as integer = 500

            int sum=0;// declare sum as intgetr = 0
            int grade;     // declare grade as integer  

            grade=input.nextInt(); // set grade as next user iput

            if (grade==-1) //  if statement if the sentinel value is set then stop
                break;

            list.add(grade); // adds the grade from the grade variable to the LinkedList
            sum=sum+grade;// put the value of sum to sum and the new grade

            if (grade>max) // if statement if grade is more than the max then sets max as the grade
                max=grade;
            if (grade<min) // if statement if grade is less than the min then sets min as the grade
                min=grade;

            System.out.println("The course name: "+ course); // prints message of the course name entered
            System.out.println("Number of Scores :"+list.size()); // sits the number of scores using the size of the list
            System.out.printf("The Average Score: %.2f" ,(double)sum/list.size()); // calculates average to 2 decimal values using the sum divided by the length of the list
            System.out.println(); // goes to next line
            System.out.println("The Minimum Score: "+min); // sets the minimum value to min
            System.out.println("The Maximum Score :"+max);// sets the minimum value to min
            answer = JOptionPane.showConfirmDialog(null," Would you like to continue?"); // sets the value of the variable answer to confrim dialog box
        } while (answer == 0);  // sets the condition for do loop to answer == o so that it would continue only if the yes is selected

    }
}

Answer 1

I think the following lines are incorrect:

int max=-100; // declare max as integer = -100
 int min=500;//declare min as integer = 500

They should be:

int max= 500; // declare max as integer = -100
 int min=-100;//declare min as integer = 500

Also they should be moved outside do-while .

Answer 2

You need another do..while for each score

     int grade;     // declare grade as integer  
     do{
        grade=input.nextInt(); // set grade as next user iput

        if(grade==-1) //  if statement if the sentinel value is set then stop
             break ;

         list.add(grade); // adds the grade from the grade variable to the LinkedList
         sum=sum+grade;// put the value of sum to sum and the new grade

         if(grade>max) // if statement if grade is more than the max then sets max as the grade
             max=grade;
         if(grade<min) // if statement if grade is less than the min then sets min as the grade
             min=grade;
     } while (true);

Answer 3

I would start by programming to the List interface (instead of the concrete collection) and I would prefer the diamond operator <> (available Java 7+). Next, I would initialize max and min to Integer.MIN_VALUE and Integer.MAX_VALUE respectively (because no int is smaller than the first or, it follows, larger than the second). Then I'd prefer Math.max(int, int) and Math.min(int, int) . Finally, I suggest you get all the values before you display statistics. Something like,

List<Integer> list = new LinkedList<>();
int answer = 1;
int max = Integer.MIN_VALUE;
int min = Integer.MAX_VALUE;
int sum = 0;
do {
    System.out.print("Please enter the name of the course:");
    String course = input.nextLine();
    System.out.printf("Please enter the scores for %s on a single "
            + "line and type a -1 at the end%n", course);
    int grade = input.nextInt();
    if (grade == -1) {
        break;
    }
    System.out.printf("Course %s, Grade %d%n", course, grade);
    list.add(grade);
    sum += grade;
    max = Math.max(max, grade);
    min = Math.min(min, grade);
    answer = JOptionPane.showConfirmDialog(null,
            "Would you like to continue?");
} while (answer == 0);
System.out.println("Number of Scores :" + list.size());
System.out.printf("The Average Score: %.2f%n",
        sum / (double) list.size());
System.out.println("The Minimum Score: " + min);
System.out.println("The Maximum Score :" + max);

Answer 4

It looks like an error with where and what you're setting the max and min values to. It should be:

int min = -100;
int max = 500;