如何在类中创建一个成员函数，该成员函数返回的值是该类对象的类型？

Question

Here's the question:

Define a class called Month that is an abstract data type for a month. Your class will have one member variable of type int to represent a month (1 for January, 2 for February, and so forth). Include all the following member functions: a constructor to set the month using the first three letters in the name of the month as three arguments, a constructor to set the month using an integer as an argument (1 for January, 2 for February, and so forth), a default constructor, an input function that reads the month as an integer, an input function that reads the month as the first three letters in the name of the month, an output function that outputs the month as an integer, an output function that outputs the month as the first three letters in the name of the month, and a member function that returns the next month as a value of type Month . Embed your class definition in a test program.

Here's my code:

    #include <iostream>
    #include <cstdlib>
    #include <string>
    using namespace std;

    class Month
    {
    public:
Month(char firstLetter, char secondLetter, char thirdLetter);
//Initializes month according to arguments for first 3 letters

Month(int month_number);
//Initializes month according to argument for integer between 1 and 12

Month();
//Initializes month to January

void input_integer();//Reads month as integer
void input_letter();//Reads month as first 3 letters in the name of month
int letters_to_integer(char firstLetter, char secondLetter, char thirdLetter);
//Converts first 3 letters of the month to integer equivalent of the month
string integer_to_letters(int month_number);
//Converts month integer to the first 3 letters of the name of the month
void output_integer();//Outputs the month as an integer
void output_letter();//Outputs the month as first 3 letters of the name of the month

void next_month();//Returns the next month in letters
    private:
int month_number;//Represents the month as an integer
string month_letters;//Represents the month in terms of its first 3 letters
char firstLetter, secondLetter, thirdLetter;
int next_month_number;//Represents the next month as an integer
    };

    int main()
    {
Month month1('m', 'a', 'y'), month2(7), month3;
cout<<"Object month1 is initialized as follows:\n";
month1.output_letter();
cout<<"Object month2 is initialized as follows:\n";
month2.output_letter();
cout<<"Object month3 is initialized as follows:\n";
month3.output_letter();

cout<<"Enter the first 3 letters of the month\n";
month3.input_letter();
cout<<"That month expressed as in integer is:\n";
month3.output_integer();
cout<<endl;


cout<<"Enter the month as an integer between 1 and 12:\n";
month3.input_integer();
cout<<"That is equivalent to the month of:\n";
month3.output_letter();
cout<<"in letters\n";
cout<<"The next month is: \n";
month3.next_month();
cout<<endl;

system("pause");
return 0;
    }

    Month::Month(char firstLetter, char secondLetter, char thirdLetter)
    {
month_number = letters_to_integer(firstLetter, secondLetter, thirdLetter);
month_letters = integer_to_letters(month_number);
    }

    Month::Month(int month_number)
    {
month_letters = integer_to_letters(month_number);
    }

    Month::Month()
    {
month_number = 1;
month_letters = "Jan\n";
    }

    void Month::input_integer()
    {
cin>>month_number;
month_letters = integer_to_letters(month_number);
next_month_number = month_number + 1;
    }

    void Month::input_letter()
    {
cin>>firstLetter>>secondLetter>>thirdLetter;
month_number = letters_to_integer(firstLetter, secondLetter, thirdLetter);
    }

    void Month::output_letter()
    {
cout<<month_letters;
    }

    void Month::output_integer()
    {
cout<<month_number;
    }

    int Month::letters_to_integer(char firstLetter, char secondLetter, char      thirdLetter)
    {
if ((firstLetter == 'j') && (secondLetter == 'a') && (thirdLetter == 'n'))
{
    month_number = 1;
}
else if ((firstLetter == 'f') && (secondLetter == 'e') && (thirdLetter == 'b'))
{
    month_number = 2;
}
else if ((firstLetter == 'm') && (secondLetter == 'a') && (thirdLetter == 'r'))
{
    month_number = 3;
}
else if ((firstLetter == 'a') && (secondLetter == 'p') && (thirdLetter == 'r'))
{
    month_number = 4;
}
else if ((firstLetter == 'm') && (secondLetter == 'a') && (thirdLetter == 'y'))
{
    month_number = 5;
}
else if ((firstLetter == 'j') && (secondLetter == 'u') && ( thirdLetter == 'n'))
{
    month_number = 6;
}
else if ((firstLetter == 'j') && (secondLetter == 'u') && (thirdLetter == 'l'))
{
    month_number = 7;
}
else if ((firstLetter == 'a') && (secondLetter == 'u') && (thirdLetter == 'g'))
{
    month_number = 8;
}
else if ((firstLetter == 's') && (secondLetter == 'e') && (thirdLetter == 'p'))
{
    month_number = 9;
}
else if ((firstLetter == 'o') && (secondLetter == 'c') && (thirdLetter == 't'))
{
    month_number = 10;
}
else if ((firstLetter == 'n') && (secondLetter == 'o') && (thirdLetter == 'v'))
{
    month_number = 11;
}
else if ((firstLetter == 'd') && (secondLetter == 'e') && (thirdLetter == 'c'))
{
    month_number = 12;
}
return month_number;
     }

    string Month::integer_to_letters(int month_number)
    {
string month_letters;

switch (month_number)
{
    case 1:
        month_letters = "Jan\n";
        break;
    case 2:
        month_letters = "Feb\n";
        break;
    case 3:
        month_letters = "Mar\n";
        break;
    case 4:
        month_letters = "Apr\n";
        break;
    case 5:
        month_letters = "May\n";
        break;
    case 6:
        month_letters = "Jun\n";
        break;
    case 7:
        month_letters = "Jul\n";
        break;
    case 8:
        month_letters = "Aug\n";
        break;
    case 9:
        month_letters = "Sep\n";
        break;
    case 10:
        month_letters = "Oct\n";
        break;
    case 11:
        month_letters = "Nov\n";
        break;
    case 12:
        month_letters = "Dec\n";
        break;
    default:
        month_letters = "Invalid integer for month";
        break;

}
return month_letters;
    }

    void Month::next_month()
    {
cout<<integer_to_letters(next_month_number);
    }

Sorry its indented all strange but this is what I have. My code runs just fine. The only thing I don't get how to do is the last part of the question which asks to create "a member function that returns the next month as a value of type Month." I am not understanding this at all. So in code I just output the string that is the next month. Please help me with this part. In class we just covered classes and this is the assignment. Please be as simple and basic as possible. I'm not too familiar with c++ or programming in general.

Thanks.

Answer 1

"and a member function that returns the next month as a value of type Month"

So basically your class Month needs to have a function that returns the following month as an object of type Month . For instance, if I had an object of Month that was equal to "June", and I called a function... call it getNextMonth() it should return a Month object equal to "July".

So your month class needs to have a function, presumably in the public section defined as Month getNextMonth(); I'll leave you to figure out how to define that function, but I would suggest reading up on "Copy constructors" and what happens when you return a class instance by value. Your class doesn't require any "deep copies" of any variables, so the default copy constructor should be fine, but it's good to know what is actually happening when your code runs.

Answer 2

As Basic As Possible : Return types:-written before the function name when you are defining or declaring a function ex- int main();. Instead of using void or int your question demands you to use the return type as your class ie 'Month' that you have defined.So instead of returning nothing or an int you will be returning an object of class Month