我怎样才能让我的打印语句在打印平均分数和相关字母等级的地方工作？

Question

 public static void main(String[] args)
    {

        // Defining the constants for min and max range
        final int minValue = -1;
        final int maxValue = 100;
        String message = "Welcome to Simple Gradebook!";

        promptForInt(message, minValue, maxValue);

        // Declaring variables for the loop & the sentinel variable
        int score = 0;
        boolean doneYet = false;

        do
        {
            // Input Validation
            if (score < minValue || score > maxValue)
            {
                System.err.printf("Invalid value. The acceptable range is"
                        + " between %d and %d\n"
                        + "Please try again\n", minValue, maxValue);
            }
            else
            {
                doneYet = true;
            }
        } while (doneYet == false);

    }

    public static int promptForInt(String message, int minValue, int maxValue)
    {
        // Declaring variables for the loop & the sentinel variable
        int sum = 0;
        int numStudents = 0;
        int score = 0;

        System.out.println(message);

        //Creating the sentinel loop
        do
        {
            System.out.printf("Enter the score for student #%d"
                    + "(or -1 to quit): ", numStudents);
            Scanner keyboard = new Scanner(System.in);
            score = Integer.parseInt(keyboard.nextLine());

            if (score != -1)
            {
                sum += score;
                numStudents += 1;
            }

        } while (score != -1);
        double avgScore = (double) sum / numStudents;
       
        //Passing method to this method to convert grade to letter
        convertToLetter(avgScore);
        System.out.println("The average score is: " + avgScore
                + " which equates to a " + avgScore);
        return 0;

    }

    public static char convertToLetter(double avg)
    {
        char avgScore = 0;
        // Identifying the ranges for the grade letter
        if (avgScore >= 90)
        {
            System.out.println("A");
        }
        else if (avg >= 80)
        {
            System.out.println("B");
        }
        else if (avg >= 70)
        {
            System.out.println("C");
        }
        else if (avg >= 60)
        {
            System.out.println("D");
        }
        else
        {
            System.out.println("F");
        }
        return avgScore;

    }
}

How can I get my print statement to work to where it prints the average score and the correlating letter grade? Like this... “The average score is 90.5, which equates to an A”

My input validation is not working like it should for some reason. If a number lower that -1 or higher than 100 is entered, it should give the error message and begin the loop again.

Answer 1

You're not doing anything with the result of convertToLetter(avgScore) .

Assign the result to a variable:

char grade = convertToLetter(avgScore);

Then refer to that variable when printing:

System.out.println("The average score is: " + avgScore
  + " which equates to a " + grade);
    

—--

You have a similar problem when calling promptForInt(message, minValue, maxValue) ; you need to assign the result to a variable:

score = promptForInt(message, minValue, maxValue);

Another major bug you have is your input checking code. If score is not in range, your do while loop will loop infinitely because the value of score is not changed anywhere inside the loop.

Add this line after printing the error message:

score = promptForInt(message, minValue, maxValue);

—--

In general, you must realise that variables have scope . You assigning a value to the avgScore variable declared inside the convertToLetter method has no effect whatsoever on the variable of the same name declared in your main method - they are different variables, whose scope is limited to the method in which they are declared.

Answer 2

1. You are not assigning and returning the grade letter from the function, convertToLetter correctly.
2. You are not printing the return value of the function, convertToLetter .

Write the function as shown below:

public static char convertToLetter(double avg) {
    char gradeLetter;
    // Identifying the ranges for the grade letter
    if (avg >= 90) {
        gradeLetter = 'A';
    } else if (avg >= 80) {
        gradeLetter = 'B';
    } else if (avg >= 70) {
        gradeLetter = 'C';
    } else if (avg >= 60) {
        gradeLetter = 'D';
    } else {
        gradeLetter = 'F';
    }
    return gradeLetter;
}

and then change the print statement as System.out.println("The average score is: " + avgScore + " which equates to a " + convertToLetter(avgScore));

Answer 3

This code works. Explanations after.

import java.util.Scanner;

public class Calculat {
    public static void main(String[] args) {

        Scanner keyboard = new Scanner(System.in);

        // Defining the constants for min and max range
        final int minValue = -1;
        final int maxValue = 100;

        String message = "Welcome to Simple Gradebook!";
        System.out.println(message);

        // Declaring variables for the loop & the sentinel variable
        int score = 0;
        int sum = 0;
        int numStudents = 0;

        while (true) {
            score = promptForInt(keyboard, (numStudents + 1), minValue, maxValue);
            if (score == -1) {
                break;
            }
            sum += score;
            numStudents++;
        }
        if (numStudents == 0) {
            System.out.println("No data received.");
        }
        else {
            double avgScore = (double) sum / numStudents;
            char letter = convertToLetter(avgScore);
            System.out.printf("The average score is: %.3f which equates to a %c%n",
                              avgScore,
                              letter);
        }
    }

    public static int promptForInt(Scanner keyboard, int numStudent, int minValue, int maxValue) {
        // Declaring variables for the loop & the sentinel variable
        int score = 0;
        boolean isValidScore = false;

        // Creating the sentinel loop
        do {
            System.out.printf("Enter the score for student #%d (or -1 to quit): ", numStudent);
            String line = keyboard.nextLine();
            try {
                score = Integer.parseInt(line);
                if (score < minValue || score > maxValue) {
                    System.out.printf("Invalid value. Acceptable range is between %d and %d%n",
                                      minValue,
                                      maxValue);
                }
                else {
                    isValidScore = true;
                }
            }
            catch (NumberFormatException xNumberFormat) {
                System.out.printf("Not a number: %s%n", line);
            }
        } while (!isValidScore);
        return score;
    }

    public static char convertToLetter(double avg) {
        char avgScore = 0;
        // Identifying the ranges for the grade letter
        if (avg >= 90) {
            avgScore = 'A';
        }
        else if (avg >= 80) {
            avgScore = 'B';
        }
        else if (avg >= 70) {
            avgScore = 'C';
        }
        else if (avg >= 60) {
            avgScore = 'D';
        }
        else {
            avgScore = 'F';
        }
        return avgScore;
    }
}

Method promptForInt() should accept a single score from the user and return it. It should return only a valid score.

Method main() contains the loop for gathering up all the scores.

You need to check that at least one score was entered, otherwise you can't calculate the average.

Method convertToLetter() was always assigning the value zero to avgScore , essentially making avgScore the null character.

Here is a sample run of the program.

Welcome to Simple Gradebook!
Enter the score for student #1 (or -1 to quit): 66
Enter the score for student #2 (or -1 to quit): 66
Enter the score for student #3 (or -1 to quit): 68
Enter the score for student #4 (or -1 to quit): -1
The average score is: 66.667 which equates to a D