Problem Calculating Averages (Class/pointers)

[Syrne]

Okay so I have a program that takes in up to 25 students and information for each including 5 test scores. All of that is done and working fine.

What I am trying to do now is calculate the averages of each test 1-5 and then the total average of the individual student's test averages.

for example:

Test1   Test2  Test3  Test4  Test5  Average
Student1 100     85     100    99     76     92.0
Student2 76      88     96     87     92     87.8

Average: 88.0    86.5   98.0   93.0   84.0   89.9 <--- This whole line is what I'm asking for help on

Here's my code so far:

HEADER:

using namespace std;
#ifndef STUDENT_CLASS
#define STUDENT_CLASS
class Student
{
    private:
            //Data Declaration
            int studentId;
            string firstName;
            string lastName;
            int *scores;
            double average;
            char grade;
            
            static int count;
            
            double calcAverage();
            
    public:
           //Default Constructor
           Student();
           //Deconstructor
           ~Student();
              
            //Set Declarations     
            void setId(int sX);
            void setFirst(string fN);
            void setLast(string lN);
            void setAverage(double sA);
            void setScores(int sS, int i);
            
            //Get Declarations
            int getId() const;
            string getFirst() const;
            string getLast() const;
            int getScores(int i) { return scores[i]; };
            
            char getGrade();
            
            //Calc. average function
            double getAverage() const;
            
            //Counter functions
            static int getCount();
            static void addCount() { count++; };
            
            //Display Function
            string displayData();
};
#endif

IMPLEMENTATION:

#include<iostream>
#include<iomanip>
#include<string>
#include<sstream>

using namespace std;

#include "Student.h"

int Student :: count = 0;

//Default Constructor
Student::Student()
{
         studentId = 0;
         firstName = "";
         lastName = "";
         
         average = 0.0;
         grade = ' ';
         scores = new int[5];
         
         for(int i = 0; i < 5; i++)
         scores[i] = 0;
}

Student::~Student()
{
       delete [] scores;
}
// Stringstream display function
string Student :: displayData(void)
{
       calcAverage();
       getGrade();

       stringstream strstr;
       
       strstr << left << setw(5) << studentId 
              << right << setw(5) << lastName << ", "
              << left << setw(5) << firstName
              << right << setw(5) << scores[0] 
              << right << setw(5) << scores[1] 
              << right << setw(5) << scores[2]
              << right << setw(5) << scores[3] 
              << right << setw(5) << scores[4];
              strstr << fixed << showpoint << setprecision(1);
              strstr << right << setw(8) << average;
              
             strstr << right << setw(8) << grade;
              
              return strstr.str();
}

//================================Set Mutator Function declarations=============================================
void Student::setId(int sX)
{
     studentId = sX;
}

void Student::setFirst(string fN)
{
     firstName = fN;
}

void Student::setLast(string lN)
{
     lastName = lN;
}

void Student::setAverage(double sA)
{
     average = sA;
}

void Student::setScores(int sS, int i)
{
     scores[i] = sS;
}
//================================Get Accessor Function declarations=============================================
int Student::getId() const
{
    return studentId;
}

string Student::getFirst() const
{
       return firstName;
}

string Student::getLast() const
{
       return lastName;
}

double Student::getAverage() const
{
     return average;  
}

int Student::getCount()
{
    return count;
}

//Function to calculate average of test scores
double Student::calcAverage()
{
     average = (scores[0] + scores[1] + scores[2] + scores[3] + scores[4]) / 5.0;
}

char Student::getGrade()
{
     if(average >= 90.0)
     {
        grade = 'A';
     }
     
     else if(average >= 80.0)
     {
        grade = 'B';
     }
     
     else if(average >= 70.0)
     {
        grade = 'C';
     }
     
    else if(average >= 60.0)
     {
        grade = 'D';
     }
     
     else
        grade = 'F';
}

MAIN:

#include <cstdlib>
#include <iostream>
#include <iomanip>
#include <string>

using namespace std;

#include "Student.h"

const int MAX = 25;

//Function Prototypes
void printData(Student *userData, double avg[]);
void getData(Student *userData);
bool newStudent(Student *userData, int index);

int main(int argc, char *argv[])
{
    Student *userData;
    userData = new Student[MAX];
    
    double avg[5] = {0.0};
    
    getData(userData);
    
    printData(userData, avg);
    
    delete [] userData;
    
    system("PAUSE");
    return EXIT_SUCCESS;
}

//Function to keep count of student object array
void getData(Student *userData)
{
     bool done = false;
     int index = Student::getCount();
     while (index < MAX && !done)
     {
           while(newStudent(userData, index))
           {
                 Student::addCount();
                 index++;
           }
           done = true;
     }

}

//Function to read keyboard entry data into student object
bool newStudent(Student *userData, int index)
{
     int sX;
     int sS;
     string fN;
     string lN;
     
     cout << "Students currently entered: " << index << endl;
     cout << "Enter student ID (ctrl-z to quit): ";
     cin >> sX;
     
     if(cin.eof())
     {
        system("cls");
        return false;
     }
        cin.ignore();
     
     cout << "Enter student's first name: ";
     getline(cin, fN);
     cout << "Enter student's last name: ";
     getline(cin, lN);
     
     (userData + index)->setId(sX);
     (userData + index)->setFirst(fN);
     (userData + index)->setLast(lN);
     
     cout << "Please enter 5 test scores (seperate with spaces): ";
     
     for(int i = 0; i < 5; i++)
     {
           cin >> sS;
           (userData + index)->setScores(sS,i);
     }
     system("cls");
     return true;
}

//Function to incorporate stringstream to display data on console
void printData(Student *userData, double avg[])
{    
     cout << left
          << setw(9) << "ID"
          << setw(12) << "Name"
          << setw(5) << "1"
          << setw(5) << "2"
          << setw(5) << "3"
          << setw(5) << "4"
          << setw(5) << "5"
          << setw(9) << "Average"
          << setw(7) << "Grade" << endl;
          
          
     for(int i = 0; i < Student::getCount(); i++)
     {
             cout << (userData + i)->displayData() << endl;
     }
     
      for(int i = 0; i < Student::getCount(); i++)
             {   
                  
                  for(int j = 0; j < 5; j++)
                          avg[j] = (avg[j] + (userData + i)->getScores(j)) / i;
 
            }
            
             cout << "\n" << endl;
             cout << "Average: "
                  << fixed << showpoint << setprecision(1)
                  << right
                  << setw(13) << avg[0]
                  << setw(5) << avg[1]
                  << setw(5) << avg[2]
                  << setw(5) << avg[3]
                  << setw(5) << avg[4] << endl;

}

Here's where I'm having trouble:

for(int i = 0; i < Student::getCount(); i++)
             {   
                  
                  for(int j = 0; j < 5; j++)
                          avg[j] = (avg[j] + (userData + i)->getScores(j)) / i;
 
            }
            
             cout << "\n" << endl;
             cout << "Average: "
                  << fixed << showpoint << setprecision(1)
                  << right
                  << setw(13) << avg[0]
                  << setw(5) << avg[1]
                  << setw(5) << avg[2]
                  << setw(5) << avg[3]
                  << setw(5) << avg[4] << endl;

}

This line without the (/ i) works as it should.

for(int j = 0; j < 5; j++)
   avg[j] = (avg[j] + (userData + i)->getScores(j)) / i;

It adds each test together (Let's say there's two students and both get a 100 on Test 1, it adds them totaling 200), but when I got to divide that number by the number of students entered, it doesn't work correctly.

I have also yet to figure out how to find the total average of each student's average.

Thanks a lot!

[StuXYZ]

You main problem is the algorithm that you calculate a continuous average with:
you do this:

for(int i = 0; i < Student::getCount(); i++)  
  for(int j = 0; j < 5; j++)
    avg[j] = (avg[j] + (userData + i)->getScores(j)) / i;

So what that does is effectively divide by i each time. e.g consider only 2 students with scores 3,3,3,3,3 etc. You do: ave[j]=((3/0)+3)/1). Obviously from that
expression you will get infinity.

The correct way to calculate an average, is to accumulate a total, and then divide by the number of students.

for(int j=0;j < 5; j++)
       avg[j]=0.0;
     for(int i = 0; i < Student::getCount(); i++)
       for(int j = 0; j < 5; j++)
	 avg[j] += (userData + i)->getScores(j);;
     for(int j=0;j < 5; j++)
       avg[j]/=Student::getCount();