Arrays of Objects

To access an object that is an element of an array of objects, use the usual following syntax:

To access a data member of an object that is an element of an array of objects, use the following syntax:

To call a member function for an object that is an element of an array of objects, use the following syntax:

Here is a full program example illustrating the creation and use of an array of Student objects:

#include <iostream>
#include <iomanip>
#include <fstream>
#include <cstdlib>
#include <cstring>

using std::cerr;
using std::cout;
using std::endl;
using std::fixed;
using std::ifstream;
using std::setprecision;

// Student class definition
class Student
{
private:

    char name[31]{"None"};
    double gpa{0.0};

public:

    // Constructors
    Student() = default;
    Student(const char*, double);

    // Accessor methods
    void set_name(const char*);
    const char* get_name() const;
    void set_gpa(double);
    double get_gpa() const;

    // Other methods
    void print() const;
};

// Function prototypes
int build(Student[]);
void print(const Student[], int);
void sort(Student[], int);

int main()
{
    Student student_array[10];
    int count;

    count = build(student_array);

    cout << "Unsorted List of Students\n\n";

    print(student_array, count);

    sort(student_array, count);

    cout << "\nSorted List of Students\n\n";

    print(student_array, count);

    return 0;
}

int build(Student student_array[])
{
    ifstream in_file;
    char first_name[11], last_name[21], name[31];
    double gpa;
    int count = 0;

    // Open the input file and test for failure
    in_file.open("students1.txt");
    if (!in_file)
    {
        cerr << "Error - unable to open input file\n";
        exit(1);
    }

    in_file >> first_name;
    while (in_file)
    {
        in_file >> last_name;
        in_file >> gpa;

        strcpy(name, last_name);
        strcat(name, ", ");
        strcat(name, first_name);

        // Create a Student object and copy it into
        // the array.
        student_array[count] = Student(name, gpa);
        
        /* Could do these lines instead to alter the
        existing Student object in the array.
        
        student_array[count].set_name(name);
        student_array[count].set_gpa(gpa); */

        count++;

        in_file >> first_name;
    }

    in_file.close();

    return count;
}

void print(const Student student_array[], int n)
{
    int i;
    cout << fixed << setprecision(2);

    for (i = 0; i < n; ++i)
    {
        student_array[i].print();
        cout << endl;
    }
}

void sort(Student student_array[], int n)
{
    int i, j, min;
    Student temp;

    for (i = 0; i < n - 1; ++i)
    {
        min = i;

        for (j = i + 1; j < n; ++j)
        {
            if (strcmp(student_array[j].get_name(), student_array[min].get_name()) < 0)
                min = j;
        }

        temp = student_array[i];
        student_array[i] = student_array[min];
        student_array[min] = temp;
    }
}

// Student constructor

Student::Student(const char* new_name, double new_gpa)
{
    set_name(new_name);
    set_gpa(new_gpa);
}

// Student accessor and mutator member functions

void Student::set_name(const char* new_name)
{
    strcpy(name, new_name);
}

const char* Student::get_name() const
{
    return name;
}

void Student::set_gpa(double new_gpa)
{
    if (new_gpa < 0.0)
        gpa = 0.0;
    else if (new_gpa > 4.0)
        gpa = 4.0;
    else
        gpa = new_gpa;
}

double Student::get_gpa() const
{
    return gpa;
}

// Other member functions

void Student::print() const
{
    cout << "Name: " << name << endl
         << "GPA: " << fixed << setprecision(2) << gpa << endl;
}