Data Types 1

Single or Double ? Visual Basic provides data type Single for storing single-precision floating-point numbers. Data type Double requires more memory to store a floating-point value, but is more accurate than type Single. Type Single is useful in applications that need to conserve memory and do not require the accuracy provided by type Double.

Dim statement declares variable Dim varname As type [ = initexpr ] Declaring a Variable Dim statement declares variable Dim varname As type [ = initexpr ] varname is variable name As type contains data type of variable Optional initexpr contains the initial value of a variable

Initialize a variable when declaring it Declaring a Variable Initialize a variable when declaring it New to VB .NET Declare an Integer variable and store the value 30 in the variable Dim mintYearTerm As Integer = 30

Declaring a Variable Possible to declare multiple variables on the same line Dim mintYearTerm, mintMonthTerm As Integer

Declaring Constants Declare constants with the Const statement. Constants are similar to variables – constants are values that are stored to memory locations; however, a constant cannot have its value change during program execution – constant values are generally fixed over time. Examples: Const SALES_TAX_RATE_SINGLE As Single = 0.0725F Const BIG_STATE_NAME_STRING As String = "Alaska" Const TITLE_STRING As String = "Data Entry Error" Const MAX_SIZE_INTEGER As Integer = 4000

Declaring Constants Follow these rules for assigning numeric values to constants: You can use numbers, a decimal point, and a plus (+) or minus (-) sign. Do not include special characters such as a comma, dollar sign, or other special characters. Append one of these characters to the end of the numeric constant or variable to denote a data type declaration. If you do not use these, a whole number is assumed to be Integer and a fractional value is assumed to be Double. Decimal D 40.45D Double R 12576.877R Integer I 47852I Long L 9888444222L Short S 2588S Single F 0.0725F

Strings Such as sentences, words, letters of the alphabet, names, telephone numbers& addresses. A string constant is a sequence of characters that is treated as a single item.

Strings quote1 = “ The ball game isn’t over “ quote2 = “ until it is over “ quote = quote1 & “ , “ & quote2 Console.WriteLine ( quote )  The ball game isn’t over , until it is over

Examining Variable Types IsNumeric() IsDate() System.Date.IsLeapYear (2001)  False

Boolean Data Type It stores True (1) / False (0) Any non-zero value will be considered as TRUE. These variables are combined with the logical operators.. AND, OR & NOT.

Converting Input Data Types Text property always stores string values, even if the string looks like a number. Parse method – converts a string value to an equivalent numeric value for storage to a numeric variable. Parse means to examine a string character by character and convert the value to another format such as decimal, integer, or string. Dim QuantityInteger As Integer = Integer.Parse(TextBox2.Text)

Conversion Between Data Types 1. Methods belong to the System.Convert class ToInt16 converts value to a Short ToInt32 converts value to an Integer ToInt64 converts value to a Long ToDouble converts value to a Double ToSingle converts value to a Single ToString converts value to a String

Conversion Between Data Types Dim msngInput As Single = 3.44 Dim mstrInput As String = "3.95" Dim mintOutput As Integer Dim msngOutput As Single Convert a Single to an Integer mintOutput = System.Convert.ToInt32(msngInput) Convert a String to an Integer mintOutput = System.Convert.ToInt32(mstrInput) Convert a String to a Single msngOutput = System.Convert.ToSingle(mstrInput)

Conversion Between Data Types 2. CType and named functions: CType method Dim A As string = “34.56” Dim B As Double B = CType ( A , Double) / 1.14 Older versions of VB used named functions to convert values. Examples are the CDec (convert to Decimal) and CInt (convert to Integer): PriceDecimal = CDec(TextBox1.Text) QuantityInteger = CInt(TextBox2.Text) CDate, CDec, CStr, CLng, CChar, CBool, CByte

Implicit Conversion Implicit Conversion – this is conversion by VB from a narrower to wider data type (less memory to more memory) – this is done automatically as there is no danger of losing any precision. In this example, an integer (4 bytes) is converted to a double (8 bytes): BiggerNumberDouble = SmallerNumberInteger