if statement problem.....

[JM1082]

Hi all,

I'm doing some practise exercises from a textbook but I've hit a snag and I can't see where I might be going wrong!

When using the nextDay() function, I'm expecting the date1 object to go into the next year. However, it doesn't reset the month value to 1 or increment the year value.

If you see where the error lies please leave a corrective suggestion.

Please see my code below:

// Fig. 9.19: fig09_19.cpp
// Demonstrating that class objects can be assigned
// to each other using default memberwise assignment
#include <iostream>
#include "Date.h" // include definition of class Date from Date.h
using namespace std;

int main()
{
    Date date1( 31, 12, 2004 );

    cout << "date1 = ";
    date1.print();

    date1.nextDay();

    cout << "\ndate1 = ";
    date1.print();
} // end main

// Fig. 9.17: Date.h
// Date class declaration.  Member function are defined in Date.cpp.

// prevent multiple inclusions of header file
#ifndef DATE_H
#define DATE_H

// class Date definition
class Date
{
public:
    Date( int = 1, int = 1, int = 2000 ); // default constructor
    void print();
    void nextDay();
    int monthsDays( int );
private:
    int month;
    int day;
    int year;
}; // end class Date

#endif // DATE_H

// Fig. 9.18: Date.cpp
// Date class member-function definitions.
#include <iostream>
#include "Date.h" // include definition of class Date from Date.h
using namespace std;

// Date constructor (should do range checking)
Date::Date( int m, int d, int y )
{
    month = ( m > 0 && m < 13 ) ? m : 1;
    day = ( d > 0 && d < ( monthsDays( m ) ) ) ? d : 1;
    year = ( y > 1999 && y < 2199 ) ? y : 2000;
} // end constructor Date

// return the number of days for each month
int Date::monthsDays( int m )
{
    switch ( m )
    {
        case 1: return 32;
            break;
        case 2: return 29;
            break;
        case 3: return 32;
            break;
        case 4: return 31;
            break;
        case 5: return 32;
            break;
        case 6: return 31;
            break;
        case 7: return 32;
            break;
        case 8: return 32;
            break;
        case 9: return 31;
            break;
        case 10: return 32;
            break;
        case 11: return 31;
            break;
        case 12: return 32;
            break;

    } // end switch
} // end function monthsDays

// print Date in the format mm/dd/yyyy
void Date::print()
{
    cout << month << '/' << day << '/' << year;
} // end function print

// increment the day by 1
void Date::nextDay()
{
    day++;
    switch ( month )
    {
        case 1: if ( day == 32 )
                {
                    day = 1;
                    month++;
                } // end if
            break;
        case 2: if ( day == 31 )
                {
                    day = 1;
                    month++;
                } // end if
            break;
        case 3: if ( day == 32 )
                {
                    day = 1;
                    month++;
                } // end if
            break;
        case 4: if ( day == 31 )
                {
                    day = 1;
                    month++;
                } // end if
            break;
        case 5: if ( day == 32 )
                {
                    day = 1;
                    month++;
                } // end if
            break;
        case 6: if ( day == 31 )
                {
                    day = 1;
                    month++;
                } // end if
            break;
        case 7: if ( day == 32 )
                {
                    day = 1;
                    month++;
                } // end if
            break;
        case 8: if ( day == 32 )
                {
                    day = 1;
                    month++;
                } // end if
            break;
        case 9: if ( day == 31 )
                {
                    day = 1;
                    month++;
                } // end if
            break;
        case 10: if ( day == 32 )
                {
                    day = 1;
                    month++;
                } // end if
            break;
        case 11: if ( day == 31 )
                {
                    day = 1;
                    month++;
                } // end if
            break;
        case 12: if ( day == 32 )
                {
                    day = 1;
                    month = 1;
                    year++;
                } // end if
            break;
    } // end switch
} // end function nextDay

[Salem]

> Date date1( 31, 12, 2004 );
This looks like DMY

> Date::Date( int m, int d, int y )
This expects MDY

If you added some final 'else' clauses or 'default' to your switch/case to complain loudly when you get to the unusual cases, you would have seen that.

[JM1082]

Who's a silly boy then? ;-)

[GReaper]

I noticed that in "monthsDays()", you return 29 for February! That is true only when "year" is a multiple of 4 and not of 100, or when it's a multiple of 400. Otherwise you should return 28.

EDIT: Also, your "nextDay()" won't work as you wish when February.

EDIT^2: O_o, why does your "monthsDays()" return one greater for all months?!

[Alexandre]

Because he uses < instead of <=.

[manasij7479]

Another suggestion, since your two switch-cases are somewhat similar, you could use a std::map to make the code much more 'elegant' .
Put a global map like this:

std::map<int,int> month_day=
{
    {1,32},
    {2,29},
    {3,32},
    //and so on
}

Remember that you have to have the c++0x flag enabled for the initializer list to work. Else just put an init function and insert the values with the insert member function or just by assigning to the indices .

For using it, instead of your function call just use
eg:

month_day[2] for getting a value of 29 .

[whiteflags]

Elegant you say? 30 days hath September April, June, and November, excepting February when comes the time every leap year gives it twenty-nine. A fine switch case that will make.

[manasij7479]

Elegant you say? 30 days hath September April, June, and November, excepting February when comes the time every leap year gives it twenty-nine. A fine switch case that will make.

Agreed.
I forgot one could omit break;s

[CommonTater]

Interested in the easy way?

// is this leap year  1 = yes, 0 = no
int IsLeapYear(int Year)
  { return !(Year % 4); }


// how many days this month
int DaysPerMonth(int Month, int Year)
  { int days[] = {0,31,28,31,30,31,30,31,31,30,31,31,31};
     if (IsLeapYear(Year))
       days[2]++;
     return days[Month]; }


// get tomorrow's date
void GetTomorrow(int *Day, int *Month, int *Year)
  { (*Day)++;
     if (*Day > DaysPerMonth(*Month, *Year))
       { *Day = 1;
          (*Month)++; }  
     if (*Month > 12)
       { *Month = 1;
          (*Year)++; } }


// what day of the year is it?
int GetDayOfYear(int Day, int Month, int Year)
  { int i;
     int yday = 0;
     for (i = 1; i < Month; i++)
        yday += DaysPerMonth(i,Year);
     return yday + Day; }

Sometimes it really pays to think in smaller blobs...

EDIT: Tossed in a couple more.

[quzah]

int IsLeapYear(int Year)
  { return !(Year % 4); }

I think there are exceptions to this. Something like if it's divisible by 2000? or 200? Here we go: Leap year - Wikipedia, the free encyclopedia


Quzah.

[CommonTater]

int IsLeapYear(int Year)
  { return !(Year % 4); }

I think there are exceptions to this. Something like if it's divisible by 2000? or 200? Here we go: Leap year - Wikipedia, the free encyclopedia


Quzah.

Ummmm.... Yoiks! Do you think they could have possibly made that any more complex?

The good news is that we don't appear to be in trouble until 2100... I can live with that

[grumpy]

Ummmm.... Yoiks! Do you think they could have possibly made that any more complex?

Well, to be fair, the reason for a leap-year (a day containing an extra year) is to synchronise the calendar year with astronomical year (the time it takes for the earth to circumnavigate the sun) or seasons. Since the astronomical year is a bit more than 365 days, and people would not take kindly to years with partial days, the only correction schemes possible involve adding whole days here and there.

The alternative would have been to slow down the speed at which the earth circumnavigates the sun so it was exactly 365 days. If you think the scheme of leap-years is complex, bear in mind it was much simpler than devising a machine that could slow down the earth without killing everyone on the planet.

[CommonTater]

Well, to be fair, the reason for a leap-year (a day containing an extra year) is to synchronise the calendar year with astronomical year (the time it takes for the earth to circumnavigate the sun) or seasons. Since the astronomical year is a bit more than 365 days, and people would not take kindly to years with partial days, the only correction schemes possible involve adding whole days here and there.

The alternative would have been to slow down the speed at which the earth circumnavigates the sun so it was exactly 365 days. If you think the scheme of leap-years is complex, bear in mind it was much simpler than devising a machine that could slow down the earth without killing everyone on the planet.

LOL... Ya think???

Warning... totally untested...

// is this leap year  1 = yes, 0 = no
int IsLeapYear(int Year)
  { if (! (Year % 100))
      Year /= 100;
    return !(Year % 4); }

[Elysia]

...

Sometimes it really pays to think in smaller blobs...

EDIT: Tossed in a couple more.

It also helps to use references where proper and not pointers and indent properly.

[GReaper]

As I said ( seems noone reads my posts ), this is how you get if current is a leap year:

bool IsLeapYear(int Year)
{
    return (!(Year % 4) && (Year % 100)) || !(Year % 400);
}