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Classes and objects

This is a discussion on Classes and objects within the C++ Programming forums, part of the General Programming Boards category; Need a help please. I have a program calculating average of students grades: Code: #include <string> #include <iostream> #include <iomanip> ...

  1. #1
    just started learning
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    Classes and objects

    Need a help please. I have a program calculating average of students grades:

    Code:
    #include <string>
    #include <iostream>
    #include <iomanip>
    #include <fstream>
    
    
    using namespace std;
    
    
    const int TOTAL_STUDENTS = 10;                
    const int TOTAL_GRADES = 10;                 
    
    
    void readInput(fstream *file, string[], int grades[][TOTAL_GRADES]);          
    void calcAvg(string names[], int grades[][TOTAL_GRADES], float average[]);    
    void printData(string names[], int grades[][TOTAL_GRADES], float average[]);  
    
    
    int main()
    {
      string names[TOTAL_STUDENTS];               
      int grades[TOTAL_STUDENTS][TOTAL_GRADES];  
      float average[TOTAL_STUDENTS];             
      fstream inputfile;                          
      string fileName;                            
    
    
      cout << "Hello there!" << endl;
      cout << "This is a program to calculate students' average test scores" << endl;
      cout << "-------------------------------------------------------------" << endl;
    
    
      cout << "Now, enter the file name: ";   
      cin >>  fileName;
      cout << endl;
    
    
        inputfile.open(fileName.c_str());
    
    
        if(inputfile.is_open())
        {
            readInput(&inputfile, names, grades);
            calcAvg(names, grades, average);
            printData(names, grades, average);
        }
        else
      {
       cout << "Please enter a correct file name or make sure file is in the same directory as the program." << endl;
    
    
       return -1;
      }
    
    
      inputfile.close();
    
    
      return 0;
    }
    
    
    void readInput(fstream *file, string names[], int grades[][TOTAL_GRADES])
    {
      for(int i = 0; i < TOTAL_STUDENTS; i++)
        {
         *file >> names[i];
       for(int j = 0; j < TOTAL_GRADES; j++)
         {
          *file >> grades[i][j];
         }
        }
    }
    
    
    void calcAvg(string names[], int grades[][TOTAL_GRADES], float average[])
    {
        float sum;
        for(int i = 0; i < TOTAL_STUDENTS; i++)
        {
            sum = 0;
            for(int j = 0; j < TOTAL_GRADES; j++)
            {
          sum += grades[i][j];
            }
            sum = (float)sum/TOTAL_GRADES;
            average[i] = sum;
        }
    }
    
    
    void printData(string names[], int grades[][TOTAL_GRADES], float average[])
    {
        for(int i = 0 ; i < TOTAL_STUDENTS; i++)
        {
            cout << names[i] << " ";
            for(int j = 0; j < TOTAL_GRADES; j++)
            {
                cout << grades[i][j] << " ";
            }
            cout << fixed << showpoint << setprecision(2) << average[i] << endl;
        }
    }
    I need to re-write this program in classes. I have header file:
    Code:
    #ifndef STUDENTTYPE_H
    #define STUDENTTYPE_H
    #include <iomanip>
    
    
    const int TOTAL_STUDENTS = 10;
    const int TOTAL_GRADES = 10;
    
    
    class StudentType
    {
      public:
        StudentType();
        readInput(ifstream&):void;
        calcAvg():void;
        printData(ostream&) const:void;
      private:
        string names;
        int grades[TOTAL_GRADES];
        float average;
    };
    
    
    #endif // STUDENTTYPE_H
    I am OK with main program. But I don't know how the implementation file should look like. Any suggestions please?
    Code:
    #include "StudentType.h"
    #include <iostream>
    
    
    
    
    StudentType::StudentType()
    {
      name = "";
      for (int i=0; i<TOTAL_STUDENTS; i++)
      {
        grades[i]={0};
      }
      average = 0.0;
    }
    ??????
    Thank you

  2. #2
    SAMARAS std10093's Avatar
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    You have to implement the functions (actually you have almost the body of them already).
    As you implemented the constructor , you shall do the other functions.
    I mean you write
    Code:
    StudentType::functionName(parameterList)
    {
          /*body of the function*/
          /*because of the operator :: you get access to the private fields of StudentType class*/
    }
    I hope that I understood the problem and this helps
    Nurlana likes this.

  3. #3
    C++ Witch laserlight's Avatar
    Join Date
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    Location
    Singapore
    Posts
    21,712
    I suggest overloading operator>> and operator<< for I/O instead:
    Code:
    class StudentType
    {
    public:
        StudentType();
        void calculateAverage();
        friend std::istream& operator>>(std::istream& in, StudentType& student);
        friend std::ostream& operator<<(std::ostream& out, const StudentType& student);
    private:
        std::string name;
        int grades[TOTAL_GRADES];
        float average;
    };
    Take a look at your previous implementation of readInput. You have this part to read the data for one student:
    Code:
    *file >> names[i];
    for(int j = 0; j < TOTAL_GRADES; j++)
    {
        *file >> grades[i][j];
    }
    So, all you need to do is to implement operator>> using the same thing, e.g.,
    Code:
    std::istream& operator>>(std::istream& in, StudentType& student)
    {
        in >> student.name;
        for (int i = 0; i < TOTAL_GRADES; ++i)
        {
            in >> student.grades[i];
        }
        return in;
    }
    This way, your readInput function becomes:
    Code:
    void readInput(fstream& file, StudentType students[])
    {
        for (int i = 0; i < TOTAL_STUDENTS; ++i)
        {
            file >> students[i];
        }
    }
    Notice that I made file an fstream& instead of an fstream*.

    Likewise, your calcAvg function will loop over the students and call the calculateAverage member function for each of them (or you can change it such that operator>> will call calculateAverage), and then your printData function will loop over the students and use the operator<< to print each of them.
    Nurlana likes this.
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  4. #4
    just started learning
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    Thank you, guys. It did help a lot!

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