C# Program to store multiple student record with name, grade1 - grade5, and average

Question

I am trying to create a program that takes user input for the amount of students and then with that in mind prompt for 5 grades and an average per student.

An example of a student record would be as follows:

Student #...... Grade1..... Grade2..... Grade3..... Grade4..... Grade5..... Average

Code so far (Probably not correct in anyway):

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Question_Two
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Input the number of students: ");
            int n = int.Parse(Console.ReadLine()); 
            Student[] students = new Student[6];

            string studentId = "Student 1"; //error here
            students[0].addGrade(double.Parse(studentId)); // or error here

            double value;
            value = double.Parse(Console.ReadLine());
            students[1].addGrade(value);

            value = double.Parse(Console.ReadLine());
            students[2].addGrade(value);

            value = double.Parse(Console.ReadLine());
            students[3].addGrade(value);

            value = double.Parse(Console.ReadLine());
            students[4].addGrade(value);

            value = double.Parse(Console.ReadLine());
            students[5].addGrade(value);

            students[6].getAverage();
        }

        public class Student
        {
            private ArrayList grades;

            public Student()
            {
                grades = new ArrayList();
            }

            public void addGrade(double val)
            {
                grades.Add(val);
            }

            public double getAverage()
            {
                double avg = 0;
                for (int i = 0; i < grades.Count; i++)
                {
                    avg += (double)grades[i];
                }
                avg /= grades.Count;
                return avg;
            }
        }
    }
}

I am not sure where to go from here as I have an error when storing the name into the array.

Answer 1

You can not parse a string "Student 1" to double like in the following code:

   string studentId = "Student 1"; //error here
   students[0].addGrade(double.Parse(studentId)); 

I don't know what you want to the result to be. But make sure that the student id is a numeric value (can be in string form). You can use the following code to get what you want.

        Console.WriteLine("Input the number of students: ");
        int numberOfStudents = int.Parse(Console.ReadLine());

        Student student = new Student();

        string studentId = "1";
        student.addGrade(double.Parse(studentId));

        double value;
        value = double.Parse(Console.ReadLine());
        student.addGrade(value);

        value = double.Parse(Console.ReadLine());
        student.addGrade(value);

        value = double.Parse(Console.ReadLine());
        student.addGrade(value);

        value = double.Parse(Console.ReadLine());
        student.addGrade(value);

        value = double.Parse(Console.ReadLine());
        student.addGrade(value);

        double avarageNumber = student.getAverage();

Answer 2

Creating an array with new does not create each individual element (except primitives like int ). You need to call new for every item in the array:

class Program
{
    static void Main(string[] args)
    {
        Console.WriteLine("Input the number of students: ");
        int n = int.Parse(Console.ReadLine()); 

        // Create array of size n (instead of 6)
        // Array is created but individual Students are not created yet!
        Student[] students = new Student[n];

        // Use a loop to get all student info
        for (int s = 0; s < n; s++) {
            string studentId = $"Student{s+1}";

            // Important! Need to create a student object
            students[s] = new Student(studentId);

            // Use another loop to get grades
            for (int g = 0; g < 5; g++) {
                double grade = double.Parse(Console.ReadLine());
                students[s].addGrade(grade);
            }

            // Print average
            Console.WriteLine($"{students[s].id} average = {students[s].getAverage()}");
        }
    }

Also, modify the Student class to have an id

    public class Student
    {
        private ArrayList grades;
        public string id;

        // Accepts one parameter : an id
        public Student(string studentId)
        {
            id = studentId;
            grades = new ArrayList();
        }

        public void addGrade(double val)
        {
            grades.Add(val);
        }

        public double getAverage()
        {
            double avg = 0;
            for (int i = 0; i < grades.Count; i++)
            {
                avg += (double)grades[i];
            }
            avg /= grades.Count;
            return avg;
        }
    }
}