Question

Hey, need some help in Java. I'm stuck on one step that prevents me from doing the rest of the steps and need help on it. I also have a problem when I print databaseCourse and programmingCourse. instead of saying 5 and 7 respectively is shows 51 and 71.

Step 8: in CourseGrades, create a method, add, that takes two parameters, studentNum and grade, and changes the grade of student studetNum to the given grade, grade. studentNum represents the student position in the array and the method should print an error if input studentNum is negative of greater than max number of students in course.

Step 9: in the Driver, write statements using the add method to enter grades for 3 students in the databaseCourse and 4 students in the programmingCourse. Then print the course info again to make sure the number of enrollments reflects the number of grades you added in your course.

Step 10: in CourseGrades, create a method called avgGrade that calculates and returns the average course grade. Call this method from the driver to print the average grade for both the databaseCourse and programmingCourse.

Step 11: in the same class, create a method called maxGrade that returns the max grade and call this method from the driver to print the max grade for databaseCourse and programmingCourse.

Step 12: in the same class, create a method called topScorer that returns the number of the student with the max grade. the method should return the position of the max grade in the array which corresponds to the student number and not the max grade. Call the method from the driver to print the top scorer for databaseCourse and programmingCourse.

my CourseGrades class:

public class CourseGrades
{
   private String title;
   private int maxNumStudents;
   private int [] grades;
  
   public CourseGrades(String courseTitle, int maxStudents)
   {
       this.title = courseTitle;
       this.maxNumStudents = maxStudents;
       this.grades = new int[maxStudents];
       for (int i = 0; i < grades.length; i++)
           grades[i] = -1;
      
   }
  
   public int getNumEnrollments()
   {
       int count = 0;
       if (grades.length > 0)
           count++;
       return count;
      
   }
  
   public String toString()
   {
       String output = this.title;
       output += maxNumStudents;
       output += getNumEnrollments();
       return output;
   }
  
   public add (int studentNum, double grade)
   {
       if (studentNum < 0)
           System.out.println("Error");
       else if (studentNum > maxNumStudents-1)
           System.out.println("Error");
       else
           for (int i = 0; i < studentNum; i++)
               studentNum =
              
   }

   public double avgGrade()
   {
      
   }
  
  
  
  
  
}

my Driver:

public class CourseDriver
{
   public static void main (String[]args)
   {
       CourseGrades databaseCourse = new CourseGrades ("Database ", 5);
       CourseGrades programmingCourse = new CourseGrades("Programming ", 7);
       System.out.println(databaseCourse);
       System.out.println(programmingCourse);
  
       databaseCourse.add(3, 20);
       programmingCourse.add(4, 20);
       System.out.println(databaseCourse);
       System.out.println(programmingCourse);
   }
  
}

Answer 1

Dear Student,

Reason for issue and solution for the issue:

I also have a problem when I print databaseCourse and programmingCourse. instead of saying 5 and 7 respectively is shows 51 and 71.

Reason:

You are declaring an array size of 5 for the database. So your array size is 5. Below line grades.length will be true.

So, even none of the grades are entered the count is incrementing and eventually, you could see it as 51.

if (grades.length > 0)
       count++;

Also, there is a formatting issue in your toString. You are directly appending, grade and enrollment. I have added meaningful printout statements in the toString method.

I have developed the code for all the requirements.

Please use any editor for testing the code

Feel free to comment if you have any queries. I have provided adequate comments for your understanding.

I am pasting the code and output.

Code:

--------------------------------------------------------------

public class CourseGrades {
   private String title;
   private int maxNumStudents;
   private int[] grades;

   public CourseGrades(String courseTitle, int maxStudents) {
       this.title = courseTitle;
       this.maxNumStudents = maxStudents;
       this.grades = new int[maxStudents];
       for (int i = 0; i < grades.length; i++)
           grades[i] = -1;

   }

   public int getNumEnrollments() {
       int count = 0;
       /*
       * Reason for error you are intializing array with size in constructor. So
       * grades length is always positive. So you are seeing output as 51 and 41, even
       * if you didn't add any student to the course.
       */

       // if (grades.length > 0)
       // count++;
       // see if the grades of the students are greater than -1 for all the students.
       // increment the count when it is greater than -1
       for (int i = 0; i < grades.length; i++) {
           if (grades[i] > -1)
               count++;
       }

       return count;

   }

   // added maximum number of students: string for better understanding of the
   // output.
   public String toString() {
       String output = this.title;
       output += " maximum number of students: ";
       output += maxNumStudents;
       output += " ,enrolled students : ";

       output += getNumEnrollments();
       return output;
   }

   // When we speak of position, we start with 1, but in array index starts from
   // zero.
   // grades[studentNum-1]=grade, so I am assigning grade by decreasing the
   // position by 1

   public void add(int studentNum, int grade) {

       if (studentNum < 0)
           System.out.println("Error");
       else if (studentNum > maxNumStudents)
           System.out.println("Error");
       else {
           /*
           * for (int i = 0; i < studentNum; i++) studentNum =
           */

           grades[studentNum - 1] = grade;
       }

   }

   public double avgGrade() {
       double sum = 0;
       for (int i = 0; i < grades.length; i++)
           sum = sum + grades[i];

       return sum / (grades.length);

   }

   //traverse the array and find maximum value.
   public int maxGrade() {
       //assign first element to the max variable for initialization
       int max = grades[0];
       for (int i = 0; i < grades.length; i++) {
           if (grades[i] > max) {
               max = grades[i];
           }

       }
       return max;
   }

   //get the maximum grade from maxGrade function, then iterater over array to find the
   //position of the max score.
   public int topGrade() {
       //highest grade of the array
       int max = maxGrade();
       int position = 0;
       for (int i = 0; i < grades.length; i++) {
           if (grades[i] == max) {
               position = i + 1;
           }

       }
       return position;
   }

}

-------------------------------

public class CourseDriver {
   public static void main(String[] args) {
       //create course object
       CourseGrades databaseCourse = new CourseGrades("Database ", 3);
       CourseGrades programmingCourse = new CourseGrades("Programming ", 5);
       System.out.println(databaseCourse);
       System.out.println(programmingCourse);

       databaseCourse.add(3, 20);
       databaseCourse.add(1, 30);
       databaseCourse.add(2, 40);

       System.out.println("Database course average: " + databaseCourse.avgGrade());
       System.out.println("Database maximum grade: " + databaseCourse.maxGrade());

       System.out.println("Database maximum grade position: " + databaseCourse.topGrade());

       programmingCourse.add(1, 20);
       programmingCourse.add(2, 30);
       programmingCourse.add(3, 40);
       programmingCourse.add(4, 50);
       programmingCourse.add(5, 60);
       System.out.println("Programming course average: " + programmingCourse.avgGrade());
       System.out.println("Programming maximum grade: " + programmingCourse.maxGrade());

       System.out.println("Programming maximum grade position: " + programmingCourse.topGrade());

       System.out.println(databaseCourse);
       System.out.println(programmingCourse);
   }

}
-----------------------------

Output: