How do you use a method to calculate 1 array parameter of grades and returns the total of the array?

Question

My schoolwork is asking me to write a Java program. I'm not getting something quite right.

Basically I have to create a Java method that gets a user to enter x amount of grades (users choice), store the grades in an array and then add the grades in the array up to be called in the main method.

Here's my code:

import java.util.Scanner;

public class Sample {

    public static void main(String[] args) {
        Scanner keyboard = new Scanner(System.in);

        System.out.println("Hello Drews, how many total grades do you want to process?");
        int numberOfGrades = keyboard.nextInt();

        int [] storeGrades = new int[numberOfGrades];
    }

    public static int getTotalScore(int numberOfGrades[]) {
        Scanner keyboard = new Scanner(System.in);
        int getTotalScore;
        int []storeGrades;

        for (int i = 0; i < getTotalScore; i++) {
            System.out.println("Please enter grade " + (i + 1) + ": ");
            int userGradeNumbers = keyboard.nextInt();
            storeGrades[i] = userGradeNumbers;
            sum += userGradeNumbers;
        }
    }
}

I'm getting an error at "sum" that it hasn't been resolved to a variable? It won't let me initialize sum within the for loop, nor the getTotalScore method. Why not?

Answer 1

Your code has the right intent about it, but some of the ordering of things is a little off and there are syntactical issues at the moment.

I would advocate splitting up your code into two methods (unless you're specifically prohibited from doing so based on the assignment). One method to get the grades from the user, and another to sum the grades. The reason for this, is that you end up trying to both store and sum the grades at the same time (which is technically more efficient), but that doesn't teach you how to calculate a running total by iterating over an array (which is likely the point of the lesson).

One other thing that I would call out (which may be beyond where you are in the course right now), is that when you're using a Scanner, you need to validate that the user has typed what you think they've typed. It's entirely plausible that you want the user to type a number, and they type "Avocado." Because Java is strongly typed, this will cause your program to throw an exception and crash. I've added in some basic input validations as an example of how you can do this; the general idea is:

1) Check that the Scanner has an int 2) If it doesn't have an int, ask the user to try again 3) Else, it has an int and you're good to proceed. Store the value.

One last thing about Scanners. Remember to close them! If you don't, you can end up with a memory leak as the Scanner continues to run.

Below is how I would have revised your code to do what you want. Shoot me a comment if something doesn't make sense, and I'll explain further. I left comments inline, as I figured that was easier to digest!

package executor;

import java.util.Scanner;

public class StudentGrades {

    public static void main(String[] args) {
        Scanner keyboard = new Scanner(System.in);

        // Initial prompt to the user
        System.out.println("Hello Drews, how many total grades do you want to process?");

        // This loop validates that the user has actually entered an integer, and prevents
        // an InputMismatchException from being thrown and blowing up the program.
        int numberOfGrades = 0;
        while (!keyboard.hasNextInt()) {
            System.out.println("Sorry, please enter a valid number!");
            keyboard.next();
        }

        // If the program makes it through the while loop, we know that the Scanner has an int, and can assign it.
        numberOfGrades = keyboard.nextInt();

        // Creating the array using the method getGrades().
        int[] storedGrades = getGrades(numberOfGrades, keyboard);

        // Calculating the total score using the method getTotalScore().
        int totalScore = getTotalScore(storedGrades);

        System.out.println("Total Score is: " + totalScore);
        keyboard.close();
    }

    /**
     * Asks the user to provide a number of grades they wish to sum.
     * @param numberOfGrades the total number of grades that will be requested from the user.
     * @param keyboard the scanner that the user will use to provide the grades.
     * @return the summed grades as an int.
     */
    public static int[] getGrades(int numberOfGrades, Scanner keyboard) {
        int[] grades = new int[numberOfGrades];

        // Asking the user i number of times, to enter a grade to store.
        for (int i = 0; i < numberOfGrades; i++) {
            System.out.println("Please enter grade " + (i + 1) + ":");

            // More input validation to ensure the user can't store "Cat."
            while (!keyboard.hasNextInt()) {
                System.out.println("Sorry, please enter a valid number!");
                keyboard.next();
            }

            int userEnteredGrade = keyboard.nextInt();

            // Storing the user's entry.
            grades[i] = userEnteredGrade;
        }
        return grades;
    }

    /**
     * Sums all of the grades stored within an integer array.
     * @param storedGrades the grades to be summed.
     * @return the total value of summed grades.
     */
    public static int getTotalScore(int[] storedGrades) {
        int totalScore = 0;
        for (int i = 0; i < storedGrades.length; i++) {
            totalScore += storedGrades[i];
        }
        return totalScore;
    }
}

Answer 2

First, get the grades. Then call the method to get the sum. Declare the sum and initialize it to 0 before your loop. Return it after. Like,

public static void main(String[] args) {
    Scanner keyboard = new Scanner(System.in);
    System.out.println("Hello Drews, how many total grades do you want to process?");
    int numberOfGrades = keyboard.nextInt();
    int[] storeGrades = new int[numberOfGrades];
    for (int i = 0; i < numberOfGrades; i++) {
        System.out.println("Please enter grade " + (i + 1) + ": ");
        storeGrades[i] = keyboard.nextInt();
    }
    System.out.println(getTotalScore(storeGrades));
}

public static int getTotalScore(int[] storeGrades) {
    int sum = 0;
    for (int i = 0; i < storeGrades.length; i++) {
        sum += storeGrades[i];
    }
    return sum;
}