CODEWITHSUNDEEP
c++operator-overloading
Trent Freguson
Trent Freguson

Reputation: 31

Operator Overloading C++

I am trying to create a program that will ask for input from the user, a month. Then the program will display the month, the following month, the previous month, the fifth month after and the seventh month before. I can not get the program to subtract a month, or the other following actions. I can only get it to add the next month. Any Thoughts?

#include <iostream>
#include <string>

using namespace std;

enum Month { JAN = 1, FEB, MAR, APR, MAY, JUN, JUL, AUG, SEP, OCT, NOV, DEC };

Month& operator++(Month& theMonth)
{
if (theMonth == DEC)
    theMonth = JAN;
else
    theMonth = static_cast<Month>(theMonth + 1); 

return theMonth;
}

Month& operator--(Month& theMonth)
{

if (theMonth == JAN)
    theMonth = DEC;
else
    theMonth = static_cast<Month>(theMonth - 1); 

return theMonth;
}

   ostream &operator<<(ostream &output, Month &theMonth)
{
switch (theMonth){
case JAN: output << "January";
    break;
case FEB: output << "February";
    break;
case MAR: output << "March";
    break;
case APR: output << "April";
    break;
case MAY: output << "May";
    break;
case JUN: output << "June";
    break;
case JUL: output << "July";
    break;
case AUG: output << "Augest";
    break;
case SEP: output << "September";
    break;
case OCT: output << "October";
    break;
case NOV: output << "November";
    break;
case DEC: output << "December";
    break;
}
return output;
}
istream &operator>>(istream &input, Month &theMonth)
{
int value;
input >> value;
theMonth = static_cast<Month>(value);
return input;
}




#include<iostream>
#include<string>
#include "Month.h"

using namespace std;

int main()
{
Month myMonth;

cout << "Enter Month (1-12): ";
cin >> myMonth;
cout << "You selected month, " << myMonth << " \n" << endl;
cout << "The next month after the month you entered is " << myMonth++ <<     "\n" << endl;
cout << "The month before the month you entered is " << myMonth-- << "\n" <<  endl;
cout << "Five months after the month you entered is " << myMonth+= << "\n"   << endl;
cout << "Seven months before the month you entered is " << myMonth-= << "\n" << endl;

cin.ignore();
cin.get();

return 0;
}

Upvotes: 3

Views: 58

Answers (1)

Sam Varshavchik
Sam Varshavchik

Reputation: 118435

Instead of using an enumerated value, I would suggest a distinct class, that wraps an int:

class Month {
   int month_num; // Month, 0-11. (0-January, 1-February, etc...)

public:

   // ...
};

Then, all month operations, such as increment, decrement, add n months, subtract n month, etc... -- they all become trivial modulo-12 arithmetic.

Displaying the name of the month also becomes as simple as it possibly can:

static const char * const months[] = {
   "January",
   "February",

   // etc... I'm too lazy to type

   "December"
};

So, when implementing your std::ostream operator<< overload, guess what "month[month_num]" will do for you?

operator++ becomes:

month_num=(month_num+1) % 12;

operator-- becomes

month_num=(month_num+11) % 12; // Yes, I just can't wrap negative values and modulo inside my brain, this is easier to grok...

operator+=, to add n to the month number, becomes

month_num=(month_num+n) % 12;

etc...

Upvotes: 4

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