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simple way to concatenate string buffers together。
However； concatenation is not the aim of the example。 The aim is to treat the strings as
numbers and then add the numbers so that c contains the value 3 （1 ＋ 2 = 3）。 The rewritten
version of the example is shown in Figure 3…14。 This code parses a string into an integer。
Integer is a value type； but
recognizes the methods associated
with the value types that can be used
to parse string buffers
Dim a As Integer = Integer。Parse（〃1〃）
Dim b As Integer = Integer。Parse（〃2〃）
Dim c As Integer = a ＋ b
Variable c contains Variables a and b are assigned
the value 3 values that represent the
parsed string buffers
Figure 3…14。 Parsing strings into integers before doing the arithmetic
The type Integer has a Parse（） method that can be used to turn a string into an integer。
The parsing works only if the buffer is a valid number。 If the buffer contains letters or an invalid
number； an error will be generated。
If the code can cope with a failed string conversion； the solution used by the parsing
routines is to generate an exception that a program could process。 Alternatively； a fail…safe way
to parse a number is to use TryParse（）； as in the following example。
Dim value As Integer
If Integer。TryParse（〃1〃； value） Then
。 。 。
End If
The TryParse（） method does not return an integer value； but instead returns a Boolean
flag； indicating whether the buffer could be parsed。 If the return value is True； then the buffer
could be parsed； and the result is stored in the parameter value。 You can parse other number
types using the same techniques （for example； Single。TryParse（））。
There are more variations in how a number can be parsed。 For example； how would the
number 100 be parsed； if the number 100 is hexadecimal？ （puters use hexadecimal numbers。）
Here is an example of hexadecimal conversion：
Imports System。Globalization
。 。 。
Public Sub ParseHexadecimal（）
Dim value As Integer= Integer。Parse（〃100〃； NumberStyles。HexNumber）
End Sub
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CH AP T E R 3 ■ L E AR N IN G AB O U T ST R I N G M A N I PU L A TI O N S 71
This example uses a variant of Parse（）； which has an additional second parameter that
represents the format of the number。 In this case； the second parameter indicates that the
format of the number is hexadecimal （NumberStyles。HexNumber； from the System。Globalization
namespace）。
■Note If you are wondering how 100 maps to 256 at the hex level； use the calculator that es with the
Windows operating system。 Switch the calculator to scientific view （View Scientific）。 Click the Hex radio
button； enter the number 100； and then click the Dec radio button。
The enumeration NumberStyles has other values that can be used to parse numbers according
to other rules。 For example； some rules handle the use of parentheses surrounding a number
to indicate a negative value。 Other rules deal with whitespace。 Here is an example：
Public Sub TestParseNegativeValue（）
Dim value As Integer = Integer。Parse（ 〃 （10） 〃； _
NumberStyles。AllowParentheses Or _
NumberStyles。AllowLeadingWhite Or _
NumberStyles。AllowTrailingWhite）
End Sub
The number 〃 （10） 〃 in this example is plicated in that it has whitespace and paren
theses。 Attempting to parse the number using Parse（） without using any of the NumberStyles
enumerated values will not work。 The enumeration AllowParentheses processes the parentheses；
AllowLeadingWhite ignores the leading spaces； and AllowTrailingWhite ignores the trailing
spaces。 Then； when the buffer has been processed； a value of –10 will be stored in the variable
value。
Other NumberStyles enumerated values allow you to process decimal points for fractional
numbers； positive or negative numbers； and so on。 This then raises the topic of processing
numbers other than Integer。 Each of the base data types； such as Boolean； Byte； and Double；
has associated Parse（） and TryParse（） methods。 Additionally； the method TryParse（） can use
the NumberStyles enumeration。 （See the MSDN documentation for details on the NumberStyles
enumerated values。）
Parsing integer values is the same； regardless of the country。 Parsing double values or dates
is not the same。 Consider the following example； which tries to parse a buffer that contains
decimal values。
Public Sub TestDoubleValue（）
Dim value As Double = Double。Parse（〃1234。56〃）
value = Double。Parse（〃1；234。56〃）
End Sub
In this example； both uses of the Parse（） method process the number 1234。56。 The first
Parse（） method is a simple parse； because it contains only a decimal point separating the
whole number from the partial number。 The second Parse（） method is more plicated in
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72 CH AP T E R 3 ■ L E A R N IN G AB OU T ST R I N G M A N I P U L AT IO N S
that a ma is used to separate the thousands of the whole number。 In both cases； the
Parse（） routines did not fail。
If you test this code； it’s possible that an exception will be generated。 In this case； the culture of
the application is to blame。 The numbers presented in the example