Re: A possible constructor bug in my program
- From: Dave <davidct1209@xxxxxxxxx>
- To: programmingblind@xxxxxxxxxxxxx
- Date: Fri, 30 Jul 2010 13:07:02 -0700
Sure; no problem. I've found, at least in languages that would allow
it, that using constructor initializer lists helps a great deal with
making the code more readable and thus, less error prone.
On 7/30/10, Joseph Lee <joseph.lee22590@xxxxxxxxx> wrote:
> Hi Dave,
> Thanks for your help. I've fixed it; turns out it was an assignment logic
> error (I should have assigned the input argument (d) to the correct value
> before assigning it to the day data).
> Cheers,
> Joseph
>
> -----Original Message-----
> From: programmingblind-bounce@xxxxxxxxxxxxx
> [mailto:programmingblind-bounce@xxxxxxxxxxxxx] On Behalf Of Dave
> Sent: Friday, July 30, 2010 8:09 AM
> To: programmingblind@xxxxxxxxxxxxx
> Subject: Re: A possible constructor bug in my program
>
> ...
> if (d < 1)
> this->day = 1;
> else if (d > days_per_month(month, y))
> this->day = days_per_month(month, y);
> else day_error = false;
> this->day = d;
> // do you want to do this even when the day is invalid (i.e. set the
> instance day to the passed in day)? In this case, you should probably
> use braces to clarify the logic here; he else above only executes the
> single statement after itthis->year = y;
> ...
>
> On 7/30/10, Joseph Lee <joseph.lee22590@xxxxxxxxx> wrote:
>> Hi guys,
>> I'm working on a Date class to store month, day and year and print out the
>> date in question. I've defined three constructors - a default one (Jan 1,
>> 1900), a constructor to take month as number (int m, int d, int y) and
>> another for taking month name as string (string m_name, int d, int y). To
>> help me set up the object correctly, I've implemented several helper
>> functions such as leap year test and an accessor to return days per month
>> for that particular month.
>> Here's the scenario with my code (in C++):
>> * Class name: Date.
>> * Encapsulated data: three ints (month, day, year) and a string
>> (month_name).
>> * Member functions: Three constructors (default, two parameterized ones),
>> two print functions (numeric date output and alpha date output).
>> * Private helpers: leap year test (bool), return month name for a month
>> number (string), return month number for a month name (int), days per
> month
>> (int).
>> // Code:
>>
>> // Second parameterized constructor: month as name.
>> // A bit more complicated than last time, but a bit easier at first
> glance.
>> // Use the helper function to get the month number based on a month name
>> e.g. July for 7.
>> // In case of wrong input, which I need to check regularly, send out an
>> error message and set the correct date.
>> // For instance, if one types one/1/2010, I should set it to
>> current_month/1/2010 e.g. 7/1/2010.
>> // It'll be better to leave the other guys alone and just put the current
>> month name to the screen. However, becauswe of the framework rule, I need
> to
>> put in 1/1/1900.
>> Date::Date(string m_name, int d, int y)
>> {
>> month = number(m_name);
>> month_name = name(month);
>> bool day_error = true; // To check for date entry.
>> if (d < 1)
>> this->day = 1;
>> else if (d > days_per_month(month, y))
>> this->day = days_per_month(month, y);
>> else day_error = false;
>> this->day = d;
>> this->year = y;
>> // After our checking code...
>> if (day_error)
>> {cout << "Error: invalid day entered: " << d << endl;
>> cout << "Day reset to: " << day << endl;
>> this->print_numeric();
>> }
>> }
>> // End of constructors.
>>
>>
>> // Other needy ones...
>>
>> // Print date in numeric form e.g. 7/1/2010.
>> void Date::print_numeric() const
>> {
>> cout << month << "/" << day << "/" << year << endl;
>> }
>>
>> // Print date in alpha form e.g. July 1, 2010.
>> void Date::print_alpha() const
>> {
>> cout << month_name << " " << day << ", " << year << endl;
>> }
>>
>>
>> // The following are helper functions - just to help out our Date object.
>>
>> // Leap year test: A leap year is ones divisible by 4 and if they are
>> divisible by 400.
>> // For instance, 1700, 1800, 1900 and 2100 are regular years and 1996,
> 2000
>> and 2012 are leap years.
>> // This function will check the year (the int argument) to see if the
>> remainder of modulus 4 is zero or not - useful for putting February 29th.
>> bool Date::is_leap(int y) const
>> {
>> return (y % 4 == 0 && (y % 100 != 0 || y % 400 == 0));
>> }
>>
>> // Days per month: 30 for April, June, September and November, 31 for
> others
>> except Feb.
>> // In case of February, use is_leap to help determine whether it should be
>> 28 (false) or 29 (true).
>> int Date::days_per_month(int m, int y) const
>> {
>> if (m == 1 || m == 3 || m == 5 || m == 7 || m == 8 || m == 10 || m == 12)
>> return 31;
>> if (m == 4 || m == 6 || m == 9 || m == 11) return 30;
>> if (m == 2)
>> {
>> if (is_leap(y)) return 29;
>> else return 28;
>> } return 0; // can never reach this point
>> }
>>
>> So, for example, if I type "Jan 32, 2010" into the console (all three
>> variables using separate output), I'm supposed to get an error message
> about
>> invalid input, then the day should be reset to days per month, which is
> 31.
>> In my case, it does not happen - the "day" in the constructor is set to
> the
>> date I've entered no matter what e.g. it'll print 1/32/2010 via
>> print_numeric function. After extensive testing, I found that it must be a
>> constructor error (my instructor was a bit puzzled about this code as
> well).
>> Thanks for your considerations on fixing this problem.
>> Cheers,
>> Joseph
>>
>>
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