Question

The private member function DayofYear: :check_date in Display 10.4 allows some illegal dates to get through, such as February \(30 .\) Redefine the member function DayofYear: :check_date so that it ends the program whenever it finds any illegal date. Allow February to contain 29 days, so you account for leap years. (Hint: This is a bit tedious and the function definition is a bit long, but it is not very difficult.

Short answer

Answer: The redefined DayofYear::check_date function handles illegal dates by first checking if the given year is a leap year (divisible by 4, not divisible by 100, or divisible by 400). Based on the month, it then checks if the day value is within the valid range for that month, considering leap years for February. If the day is out of the valid range, the function outputs an error message and terminates the program.

Step-by-step solution

Identify rules for validating dates

To validate the date, we need to consider the days range for each month in any year: - January: 1-31 - February: 1-28 (or 1-29 in leap years) - March: 1-31 - April: 1-30 - May: 1-31 - June: 1-30 - July: 1-31 - August: 1-31 - September: 1-30 - October: 1-31 - November: 1-30 - December: 1-31 And be aware of the leap year rule: - Leap year occurs when the year is divisible by 4, not divisible by 100, or divisible by 400.

Create the DayofYear::check_date function

Before we continue, make sure you understand the code from Display 10.4, including the class definition and the implementation of check_date function. Now, redefine the DayofYear::check_date function to follow these basic rules: 1. Check if the year is a leap year. If it meets the aforementioned conditions, set a variable flag (e.g., isLeapYear) to true. 2. Based on the month, check if the day value is within the valid range for that month. If the day is out of the range, output an error message and end the program. 3. If the function has not ended the program, it proceeds through the Days without any issue. ```cpp //Definition of member function check_date void DayofYear::check_date() { bool isLeapYear = ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0)); int daysInMonth; if(month == 2) daysInMonth = (isLeapYear) ? 29 : 28; else if(month == 4 || month == 6 || month == 9 || month == 11) daysInMonth = 30; else daysInMonth = 31; if(day <= 0 || day > daysInMonth) { std::cout << "Illegal date! Program will terminate." << std::endl; exit(1); } } ``` Now, the DayofYear::check_date function will correctly handle illegal dates, including the leap years, and terminate the program when it encounters an illegal date.

Key concepts

Date Validation

Date validation is a crucial part of any application that deals with calendars, schedules, or timelines. It ensures that the provided date is legally valid by checking if it fits the expected pattern of month, day, and possibly year.
When implementing date validation in a C++ program, you need to consider the number of days each month can have. This varies from 28 to 31:

• January, March, May, July, August, October, and December have 31 days.
• April, June, September, and November have 30 days.
• February varies, having 28 or 29 depending on whether it's a leap year.

These checks ensure that the date is within the ordinary calendar rules. If the date surpasses the maximum days of any month, it means the date is illegal, prompting corrective measures or error reporting.

Leap Year Calculation

Leap year calculation is a pivotal feature of any date validation process, especially when dealing with February. The reason February has either 28 or 29 days is that every four years it gains an extra day to account for the annual astronomical shift.
To ascertain whether a year is a leap year, you can follow these rules:

• A year must be divisible by 4.
• If it is divisible by 100, it must also be divisible by 400 to be a leap year.

For instance, the year 2024 will be a leap year because it is divisible by 4 and not a century year. However, 2100 will not be a leap year despite being divisible by 4 because it is not divisible by 400.
This leap year logic is vital in determining if February's day count should be adjusted to 29 and maintains date accuracy.

Member Functions

In C++ programming, member functions are functions that are part of a class. They operate on objects of the class and typically manipulate or retrieve private data members of the class.
For date validation, a member function like `check_date` may belong to a `DayofYear` class. This connects the function directly to the date-keeping object, encapsulating its functionality.
Using member functions has its benefits:

• Encapsulation: You can shield data from unauthorized access.
• Reusability: Functions can be reused with different objects.
• Organization: Member functions keep related operations together, improving code readability.

The `check_date()` function effectively makes use of these benefits by accessing month and year data members to validate date entry.

Error Handling

Error handling is crucial when dealing with potentially incorrect or illegal operations, such as invalid dates. By implementing error handling, a program can manage unexpected situations without crashing.
In the provided solution, the approach is to terminate the program when an illegal date is detected. This ensures data integrity, although it's not always the best practice in larger systems.
More refined error handling could involve:

• Outputting a message and prompting the user to re-enter information.
• Logging the occurrence for record-keeping purposes.
• Returning an error code or exception handling to allow the program more graceful exit or recovery.

By incorporating these strategies, applications become robust, user-friendly, and maintainable.