Introduction to Classes

Source Code from Notes

Example

Example to illustrate accessing member data and member functions for a class

#include <iostream.h>

//Declaration of Class

class Savings
{
        public:
        unsigned      account_number;
        float         balance;

        unsigned deposit(unsigned amount)
        {
                balance += amount;
                return balance;
        }
};

//main program which uses class Savings
main()
{
        Savings a;   // declare an object a of data type Savings
        Savings b;   // declare an object b of data type Savings

        a.account_number = 1;  // set account number for a to 1
        a.balance = 0.0;       // set balance for a to 0
        a.deposit(10.0);       // deposits 10 pounds to a

        b.account_number = 2;  // set account number for b to 2
}



Example


#include <iostream.h>
// class declaration
class Rational
{
        public:
                void assign (int, int);
                double convert ();      // convert fraction to double
                void invert ();         // invert fraction
                void print ();          // print as a fraction
        private:
                int     num, den;
};
// main program
main()
{
        Rational x;

        x.assign(22,7);
        cout << " x = " ;
        x.print();
        cout << " = " << x.convert() << "\n";
        x.invert();
        cout << "1/x = ";
        x.print();
        cout << "\n";
}

//Rational function definitions
void Rational::assign(int n, int d)
{
        num = n;
        den = d;
}
double Rational::convert()
{
        return double(num)/den;
}
void Rational::invert()
{
        int temp = num;
        num = den;
        den = temp;
}
void Rational::print()
{
        cout << num << "/" << den;
}




Example - Constructor


Add Constructor to Student class example


#include >iostream.h<
class Student
{
        public:
        Student()
        {
                module_hours = 0;
                average_marks = 0.0;
        }
        //marks - returns average marks
        float marks()
        {
                return average_marks;
        }

        //hours_worked - returns number of study hours
        float hours_worked()
        {
                return module_hours;
        }


        // other public functions

        private:
        int     module_hours;
        float   average_marks;
};

int main()
{
        Student s; // create the object and initialise it

        // print out initialised values
        cout << "hours " << s.hours_worked()
             << " average_marks " << s.marks() << "\n";

        // rest of main 
}






Constrcutor Example - Rational Class


class Rational
{
        public:
                Rational(int n, int d)
                {
                        num = n;
                        den = d;
                }
                void print();
        private:
                int num,den;
};
main()
{
        Rational x(22,7), y(-2,5);
        cout << "x = ";
        x.print();
        cout << "y = ";
        y.print();
}






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