Visual Basic Guide
Variables & Data Types
Selection
Iteration/Repetition
Revision & Practice
Procedures & Functions
Built-in Functions
Arrays
Handling Text Files
Standard Algorithms
Validation & Error Handling
Odds & Sods
Pocket Cube
Visual Basic 2010 (Console) Guide
The Date Structure
There are lots of situations where it necessary for programmers to work with dates or times. The Date structure contains many properties and methods to make this easier.
When you declare a variable of the type Date, it represents an instant in time, normally expressed as a date and time of day.
For example,
Dim now As Date = Date.Today
Console.WriteLine("Today's date is {0} ", now)
Dim currDateTime As Date = Date.Now
Console.WriteLine("The current date and time is {0} ", currDateTime)
Dim tomorrow As Date = currDateTime.AddDays(1)
Console.WriteLine("Tomorrow, it will be {0} ", tomorrow)
Dim backThen As Date = New Date(2000, 1, 1)
Console.WriteLine("The first day of they year 2000 was {0} ", backThen.DayOfWeek)
Console.ReadLine()
Type in and run the program above. Adapt the program to tell you what the day of the week was when you were born.
Creating A New DateTime
When you make a new instance of something like a date, Visual Basic uses the constructor function to make the new object. Different types have different constructors. For many, you have a choice of constructors that you want to use to set up your variable. When there is more than one constructor, we say that the constructor function is overloaded (and this is generally a good thing).
There are lots of ways to make a date or date+time variable. The following are normally all that you need,
Dim myDate As Date = New Date(year, month, day)
Dim myDateTime As Date = New Date(year, month, day, hour, minute, second)
DateTime Properties
The following properties are used to create and manipulate instances of DateTime structure.
| Property | Description | Type |
| Date | Gets the date component | DateTime |
| Day | Gets the day component | Integer |
| DayOfWeek | Gets the week day | DayOfWeek Enumeration |
| Hour | Gets the hour component | Integer |
| Millisecond | Gets the millisecond component | Integer |
| Minute | Gets the minute component | Integer |
| Month | Gets the month component | Integer |
| Now | Gets a DateTime object that is the current date and time | DateTime |
| Second | Gets the second component | Integer |
| TimeOfDay | Gets the time part of a DateTime instance | TimeSpan |
| Today | Gets a DateTime object that is the current date and time set to 00:00:00 | DateTime |
| Year | Gets the year component | Integer |
DateTime Methods
The following methods can be used to manipulate a DateTime instance. Look at how some of these are used in the example above.
| Method | Description |
| AddDays(d) | Adds d days to the DateTime |
| AddHours(h) | Adds h hours to the DateTime |
| AddMilliseconds(m) | Adds m milliseconds to the DateTime |
| AddMinutes(m) | Adds m minutes to the DateTime |
| AddMonths(m) | Adds m months to the DateTime |
| AddSeconds(s) | Adds s seconds to the DateTime |
| AddYears(y) | Adds y years to the DateTime |
| DaysInMonth(y, m) | Returns an integer equal to the number of days in month m of year y. |
| IsLeapYear(y) | Returns a Boolean (true or false) |
| ToShortDateString() | Returns a short string representation of the date component of a DateTime |
| ToShortTimeString() | Returns a short string representation of the time component of a DateTime |
| ToString() | Returns a string representation of a DateTime |
Having A Go
- Write a program that allows the user to type in a date and get the day of the week for that date.
- Write a program that tells the user whether a year entered at the keyboard is a leap year.