Question

Write a program that accepts a date in the form month/day/year and outputs whether or not the date is valid. For example \(5 / 24 / 1962\) is valid, but \(9 / 31 / 2000\) is not. (September has only 30 days.)

Short answer

Check month and day against their valid ranges after splitting the input date.

Step-by-step solution

Parse the Input

First, we need to get the input of the date in the format month/day/year. We'll split this input string into three variables: month, day, and year.

Validate the Month

Check if the month value is valid, i.e., it should be an integer between 1 and 12. If it's not, then the date is invalid.

Determine If Year is Leap Year

If the month is February, we need to check if the year is a leap year, because this affects the number of days. A year is a leap year if it is divisible by 4 but not divisible by 100, except it is divisible by 400.

Validate the Day Based on the Month

Determine the maximum number of days in the given month. For example, use 31 for January, March, May, July, August, October, December; 30 for April, June, September, November; and 28 or 29 for February, depending on whether it is a leap year. Check if the day is within the correct range for that month.

Output the Result

If all checks are passed, print that the date is valid. Otherwise, print that the date is not valid.

Key concepts

Leap Year Calculation

Understanding leap years is vital when validating dates, particularly in February which can have either 28 or 29 days. To determine if a year is a leap year, we follow a simple set of rules:

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

These rules arise from the need to keep our calendar aligned with the Earth's orbit around the Sun, which takes approximately 365.24 days. Therefore, an extra day is added every four years (in February), except in years that are divisible by 100 and not by 400. This detailed method ensures accuracy over time, preventing the calendar from drifting away from seasonal events.
For example, the year 2000 was a leap year because it is divisible by 400, while 1900 was not as it is not divisible by 400 despite being divisible by 100.

Input Parsing

Input parsing is the initial step in processing user input data effectively. In date validation, we often receive the date in a string format, such as "month/day/year". To work with this data, it needs to be split into three distinct parts: month, day, and year.
A common approach is to use the string split function, which breaks the string at each "/" sign. This produces a list or array containing three elements: the month, day, and year as separate items.
Parsing the input correctly is crucial for subsequent steps, like verifying if these entries are valid integers and checking them against month and year ranges.

Conditional Logic

Conditional logic allows us to perform checks and decisions based on certain conditions. In date validation, this primarily involves checking whether the parsed month, day, and year form a valid date.
Conditional statements, such as `if` and `else`, help execute different code paths depending on whether a condition is true or false. For instance, determining if the month number lies between 1 and 12, or verifying the day fits the standard limits of the month.
In cases like February, more complex conditions are needed to account for leap years, using logical operators to handle these nuanced checks, such as combining checks for divisibility and leap year rules.

Date Format

Recognizing and correctly handling various date formats is essential, especially when validating dates in software applications. The common format used in this exercise is "month/day/year", often used in the United States.
Different regions may use other formats (like "day/month/year" in other parts of the world), so it's crucial to understand the context in which your date data is being used.
In programming, ensuring we're working with the correct format is necessary for accurate validation and processing. Misinterpreting a date could lead to significant errors, like misunderstanding March 4th as April 3rd in different formats. Therefore, clearly defining and consistently applying a specific date format is key to avoiding such mistakes.