Initials of vb.net (Variables and Constants)

Types of Variables

You’ve learned how to declare variables and that all variables should have a type. But what

data types are available? Visual Basic recognizes the following five categories of variables:

◆ Numeric

◆ String

◆ Boolean

◆ Date

◆ Object

The two major variable categories are numeric and string. Numeric variables store numbers,

and string variables store text. Object variables can store any type of data.

Numeric Variables

You’d expect that programming languages would use the same data type for numbers. After

all, a number is a number. But this couldn’t be further from the truth. All programming languages

provide a variety of numeric data types, including the following:

◆ Integer (there are several Integer data types)

◆ Decimal

◆ Single (floating-point numbers with limited precision)

◆ Double (floating-point numbers with extreme precision)

Declearing variables

Byte Variables

Dim n As Byte

Dim A As Byte, B As Byte

A = 233

B = 50

Boolean Variables

The Boolean data type stores True/False values.

Dim running As Boolean

If running = True Then

 running = False

Else

 running = True

End If

String Variables

The String data type stores only text.

Dim aString As String

aString = “Now is the time for all good men to come ”

“to the aid of their country”

aString = “”

aString = “There are approximately 25,000 words in this chapter”

aString = “25,000”

Dim aNumber As Integer = 25000

Dim aString As String = “25,000”

Character Variables

Character variables store a single Unicode character in two bytes. In effect, characters are

Unsigned Short integers (UInt16), but the Framework provides all the tools you need to work

with characters without having to resort to their numeric values (a very common practice for

the older among us)

Dim char1 As Char = “a”, char2 As Char = “ABC”

Debug.WriteLine(char1)

Debug.WriteLine(char2)

Date Variables

Date variables store date values that may include a time part (or not),

Dim expiration As Date

The following are all valid assignments:

expiration = #01/01/2010#

expiration = #8/27/1998 6:29:11 PM#

expiration = “July 2, 2011”

expiration = Today()

Today() function returns the current date and time, while the Now() function

returns the current date.

Constants

Some variables don’t change value during the execution of a program. These variables are constants that appear many times in your code. For instance, if your program does math calculations, the value of pi (3.14159. . .) might appear many times. Instead of typing the value 3.14159 over and over again, you can define a constant, name it pi, and use the name of the constant in your code. The statement

circumference = 2 * pi * radius

is much easier to understand than the equivalent

circumference = 2 * 3.14159 * radius

Constants also have a scope and can be Public or Private. The constant pi, for instance, is usually declared in a module as Public so that every procedure can access it:

Public Const pi As Double = 3.14159265358979.