Classes

Equality Function

//DISPLAY 11.1 Equality Function 
//Program to demonstrate the function equal. The class DayOfYear
//is the same as in Self-Test Exercise 23-24 in Chapter 6.
#include <iostream>
using namespace std;

class DayOfYear
{
public:
    DayOfYear(int the_month, int the_day);
    //Precondition: the_month and the_day form a
    //possible date. Initializes the date according 
    //to the arguments.

    DayOfYear( );
    //Initializes the date to January first.

    void input( );

    void output( );

    int get_month( );
    //Returns the month, 1 for January, 2 for February, etc.

    int get_day( );
    //Returns the day of the month.
private:
    void check_date( );
    int month;
    int day;
};

bool equal(DayOfYear date1, DayOfYear date2);
//Precondition: date1 and date2 have values.
//Returns true if date1 and date2 represent the same date;
//otherwise, returns false.

int main( )
{
    DayOfYear today, bach_birthday(3, 21);

    cout << "Enter today's date:\n";
    today.input( );
    cout << "Today's date is ";
    today.output( );

    cout << "J. S. Bach's birthday is ";
    bach_birthday.output( );


if ( equal(today, bach_birthday))
        cout << "Happy Birthday Johann Sebastian!\n";
    else
        cout << "Happy Unbirthday Johann Sebastian!\n";
    return 0;
}

bool equal(DayOfYear date1, DayOfYear date2)
{
     return ( date1.get_month( ) == date2.get_month( ) &&
                date1.get_day( ) == date2.get_day( ) );
}

DayOfYear::DayOfYear(int the_month, int the_day)
                  : month(the_month), day(the_day)
{
    check_date();
}

int DayOfYear::get_month( )
{
    return month;
}

int DayOfYear::get_day( )
{
    return day;
}

//Uses iostream:
void DayOfYear::input( )
{
    cout << "Enter the month as a number: ";
    cin >> month;
    cout << "Enter the day of the month: ";
    cin >> day;
}

//Uses iostream:
void DayOfYear::output( )
{
    cout << "month = " << month
         << ", day = " << day << endl;
}


 

Equality Function as a Friend

//DISPLAY 11.2 Equality Function as a Friend 
//Demonstrates the function equal. 
//In this version equal is a friend of the class DayOfYear. 
#include <iostream>
using namespace std;
 
class DayOfYear
{
public:
    friend bool equal(DayOfYear date1, DayOfYear date2);
    //Precondition: date1 and date2 have values.
    //Returns true if date1 and date2 represent the same date; 
    //otherwise, returns false.

    DayOfYear(int the_month, int the_day);
    //Precondition: the_month and the_day form a
    //possible date. Initializes the date according 
    //to the arguments.

    DayOfYear( );
    //Initializes the date to January first.

    void input( );

    void output( );

    int get_month( );
    //Returns the month, 1 for January, 2 for February, etc.

    int get_day( );
    //Returns the day of the month.
private:
    void check_date( );
    int month;
    int day;
};

int main( )
{
//The main part of the program is the same as in Display 11.1.
}

bool equal(DayOfYear date1, DayOfYear date2)
{
    return ( date1.month == date2.month &&
                           date1.day == date2.day );
}

//The rest of this display, including the Sample Dialogue, is the same as in Display 11.1.


 

Money Class Version 1

//DISPLAY 11.3 Money Class Version 1
//Program to demonstrate the class Money.
#include <iostream>
#include <cstdlib>
#include <cctype>
using namespace std;

//Class for amounts of money in U.S. currency.
class Money
{
public:
    friend Money add(Money amount1, Money amount2);
    //Precondition: amount1 and amount2 have been given values.
    //Returns the sum of the values of amount1 and amount2.

    friend bool equal(Money amount1, Money amount2);
    //Precondition: amount1 and amount2 have been given values.
    //Returns true if the amount1 and amount2 have the same value; 
    //otherwise, returns false.

    Money(long dollars, int cents);
    //Initializes the object so its value represents an amount with the
    //dollars and cents given by the arguments. If the amount is negative,
    //then both dollars and cents must be negative.

    Money(long dollars);
    //Initializes the object so its value represents $dollars.00.

    Money( );
    //Initializes the object so its value represents $0.00.

    double get_value( );
    //Precondition: The calling object has been given a value.
    //Returns the amount of money recorded in the data of the calling object.

    void input(istream& ins);
    //Precondition: If ins is a file input stream, then ins has already been
    //connected to a file. An amount of money, including a dollar sign, has been
    //entered in the input stream ins. Notation for negative amounts is -$100.00.
    //Postcondition: The value of the calling object has been set to
    //the amount of money read from the input stream ins.
    void output(ostream& outs);
    //Precondition: If outs is a file output stream, then outs has already been 
    //connected to a file.
    //Postcondition: A dollar sign and the amount of money recorded
    //in the calling object have been sent to the output stream outs.
private:
    long all_cents;
};



int digit_to_int(char c);
//Function declaration for function used in the definition of Money::input:
//Precondition: c is one of the digits '0' through '9'.
//Returns the integer for the digit; for example, digit_to_int('3') returns 3.

int main( )
{
    Money your_amount, my_amount(10, 9), our_amount;
    cout << "Enter an amount of money: ";
    your_amount.input(cin);
    cout << "Your amount is ";
    your_amount.output(cout);
    cout << endl;
    cout << "My amount is ";
    my_amount.output(cout);
    cout << endl;

    if (equal(your_amount, my_amount))
        cout << "We have the same amounts.\n";
    else
        cout << "One of us is richer.\n";
    our_amount = add(your_amount, my_amount);
    your_amount.output(cout);
    cout << " + ";
    my_amount.output(cout);
    cout << " equals ";
    our_amount.output(cout);
    cout << endl;
    return 0;
}
Money add(Money amount1, Money amount2)
{
    Money temp;

    temp.all_cents = amount1.all_cents + amount2.all_cents;
    return temp;
}

bool equal(Money amount1, Money amount2)
{
    return (amount1.all_cents == amount2.all_cents);
}

Money::Money(long dollars, int cents)
{
    if(dollars*cents < 0) //If one is negative and one is positive


{
        cout << "Illegal values for dollars and cents.\n";
        exit(1);
    }
    all_cents = dollars*100 + cents;
}

Money::Money(long dollars) : all_cents(dollars*100)
{
    //Body intentionally blank.
}

Money::Money( ) : all_cents(0)
{
    //Body intentionally blank.
}

double Money::get_value( )
{
    return (all_cents * 0.01);
}
//Uses iostream, cctype, cstdlib:
void Money::input(istream& ins)
{
    char one_char, decimal_point,
         digit1, digit2; //digits for the amount of cents
    long dollars;
    int cents;
    bool negative;//set to true if input is negative.
 
    ins >> one_char;
    if (one_char == '-')
    {
        negative = true;
        ins >> one_char; //read '$'
    }
    else
        negative = false;
    //if input is legal, then one_char == '$'

    ins >> dollars >> decimal_point >> digit1 >> digit2;

    if ( one_char != '$' || decimal_point != '.'
         || !isdigit(digit1) || !isdigit(digit2) )


    {
        cout << "Error illegal form for money input\n";
        exit(1);
    }
    cents = digit_to_int(digit1)*10 + digit_to_int(digit2);

    all_cents = dollars*100 + cents;
    if (negative)
        all_cents = -all_cents;
}

//Uses cstdlib and iostream:
void Money::output(ostream& outs)
{
    long positive_cents, dollars, cents;
    positive_cents = labs(all_cents);
    dollars = positive_cents/100;
    cents = positive_cents%100;

    if (all_cents < 0)
        outs << "-$" << dollars << '.';
    else
        outs << "$" << dollars << '.';

    if (cents < 10)
        outs << '0';
    outs << cents;
}

int digit_to_int(char c)
{
    return (static_cast<int>(c) - static_cast<int>('0') );
}

 

The Class Money with Constant Parameters

//DISPLAY 11.4 The Class Money with Constant Parameters 
//Class for amounts of money in U.S. currency.
class Money
{
public:
    friend Money add(const Money& amount1, const Money& amount2);
    //Precondition: amount1 and amount2 have been given values.
    //Returns the sum of the values of amount1 and amount2.
friend bool equal(const Money& amount1, const Money& amount2);
    //Precondition: amount1 and amount2 have been given values.
    //Returns true if amount1 and amount2 have the same value; 
    //otherwise, returns false.

    Money(long dollars, int cents);
    //Initializes the object so its value represents an amount with the
    //dollars and cents given by the arguments. If the amount is negative,
    //then both dollars and cents must be negative.

    Money(long dollars);
    //Initializes the object so its value represents $dollars.00.

    Money( );
    //Initializes the object so its value represents $0.00.

    double get_value( ) const;
    //Precondition: The calling object has been given a value.
    //Returns the amount of money recorded in the data of the calling object.

    void input(istream& ins);
    //Precondition: If ins is a file input stream, then ins has already been
    //connected to a file. An amount of money, including a dollar sign, has been
    //entered in the input stream ins. Notation for negative amounts is -$100.00.
    //Postcondition: The value of the calling object has been set to
    //the amount of money read from the input stream ins.

    void output(ostream& outs) const;
    //Precondition: If outs is a file output stream, then outs has already been 
    //connected to a file.
    //Postcondition: A dollar sign and the amount of money recorded
    //in the calling object have been sent to the output stream outs.
private:
    long all_cents;
};

 

Overloading Operators

//DISPLAY 11.5 Overloading Operators 
//Program to demonstrate the class Money. (This is an improved version of
//the class Money that we gave in Display 11.3 and rewrote in Display 11.4.)
#include <iostream>
#include <cstdlib>
#include <cctype>
using namespace std;
         
//Class for amounts of money in U.S. currency.
class Money
{
public:
    friend Money operator +(const Money& amount1, const Money& amount2);
    //Precondition: amount1 and amount2 have been given values.
    //Returns the sum of the values of amount1 and amount2.

    friend bool operator ==(const Money& amount1, const Money& amount2);
    //Precondition: amount1 and amount2 have been given values.
    //Returns true if amount1 and amount2 have the same value; 
    //otherwise, returns false.

    Money(long dollars, int cents);

    Money(long dollars);

    Money( );

    double get_value( ) const;

    void input(istream& ins);

    void output(ostream& outs) const;
private:
    long all_cents;
};

//Any extra function declarations from Display 11.3 go here. 

int main( )
{
    Money cost(1, 50), tax(0, 15), total;
    total = cost + tax;

    cout << "cost = ";
    cost.output(cout);
    cout << endl;


cout << "tax = ";
    tax.output(cout);
    cout << endl;
    cout << "total bill = ";
    total.output(cout);
    cout << endl;
    if (cost == tax)
        cout << "Move to another state.\n";
    else
        cout << "Things seem normal.\n";
    return 0;
}

Money operator +(const Money& amount1, const Money& amount2)
{
    Money temp;
    temp.all_cents = amount1.all_cents + amount2.all_cents;
    return temp;
}

bool operator ==(const Money& amount1, const Money& amount2)
{
    return (amount1.all_cents == amount2.all_cents);
}


     //The definitions of the member functions are the same as in 
//Display 11.3 except that const is added to the function headings 
//in various places so that the function headings match the function 
//declarations in the preceding class definition. No other changes 
//are needed in the member function definitions. The bodies of the 
//member function definitions are identical to those in Display 11.3.
 

Overloading a Unary Operator

//DISPLAY 11.6 Overloading a Unary Operator
//Class for amounts of money in U.S. currency. 
class Money
{
public:
    friend Money operator +(const Money& amount1, const Money& amount2);

    friend Money operator -(const Money& amount1, const Money& amount2);
    //Precondition: amount1 and amount2 have been given values.
    //Returns amount 1 minus amount2.

    friend Money operator -(const Money& amount);
    //Precondition: amount has been given a value.
    //Returns the negative of the value of amount.

    friend bool operator ==(const Money& amount1, const Money& amount2);

    Money(long dollars, int cents);

    Money(long dollars);

    Money( );

    double get_value( ) const;

    void input(istream& ins);
    void output(ostream& outs) const;
private:
    long all_cents;
};

  //Any additional function declarations as well as the main part of the program go here.

Money operator -(const Money& amount1, const Money& amount2)
{
    Money temp;
    temp.all_cents = amount1.all_cents - amount2.all_cents;
    return temp;
}

Money operator -(const Money& amount)
{
    Money temp;
    temp.all_cents = -amount.all_cents;
    return temp;
}
           //The other function definitions are the same as in Display 11.5.