Fractional number one and a half Public Sub AddFractionalNumbersToWhole（） Dim total As Integer = CType（1。5； Integer） ＋ _ CType（1。2； Integer） If （total 2。7） Then Console。WriteLine（〃Oops； something went wrong〃） End If End Sub Using Ctype（） means to cast a Double to an Integer。 This results in a roundoff where 1。2 = 1 and 1。5 = 2。 Had DirectCast（） been used； a pilation error would result； since converting a Double to an Integer requires coercion。 Figure 2…15。 Adding fractions using the Integer data type Declaring a number with a decimal A really small number （。0） automatically creates a floating point value Public Sub AddFractionalNumbers（） Dim value As Single = 10000。0 ＋ 0。000001 Console。WriteLine（〃Value （｛0｝）〃； value） End Sub The console displays the number The variable value is 10；000 because the small number is the addition of a big insignificant from the perspective of number to a small Single。 Single can remember only 7 number digits。 10000。000001 is 10 digits of precision。 Figure 2…16。 Adding fractions using the Single data type …………………………………………………………Page 69…………………………………………………………… CH A PT E R 2 ■ L E A R N I N G A B OU T 。 N E T N U M B E R AN D V A L U E T Y P E S 47 Finishing the Calculator The original declaration of the Add（） method for the calculator worked； but had some serious limitations on what kinds of numbers could be added。 To finish the calculator； we need to declare the Add（） method using a different type； and then add the remaining operations。 We could use one of three types to declare the Add（） method： o Long： Solves the problem of adding two very large numbers like 2 billion； but has the problem that you cannot add fractional numbers like 1。5 plus 1。5。 o Double： Solves the problem of adding two very large or small numbers； and can be used to add fractional numbers。 Generally speaking； Double is a good choice； but can suffer from significance problems if a very large number is manipulated by a very small number。 o Decimal： A generally good approach and suitable for all types of precision； but also the slowest when adding； subtracting； or performing other mathematical operations。 The simplest all…around numeric data type to use is Double； as it provides good precision and is relatively fast。 The plete implementation of the calculator is as follows： Public Class Operations Public Shared Function Add（ByVal number1 As Double； ByVal number2 As _ Double） As Double Return number1 ＋ number2 End Function Public Shared Function Divide（ByVal number1 As Double； ByVal number2 As _ Double） As Double Return number1 / number2 End Function Public Shared Function Multiply（ByVal number1 As Double； ByVal number2 As _ Double） As Double Return number1 * number2 End Function Public Shared Function Subtract（ByVal number1 As Double； ByVal number2 As _ Double） As Double Return number1 number2 End Function End Class The four operations are methods with different identifiers； but identical method signa tures； making it easy to remember how to use each method。 Each of the operations would have an appropriate set of tests verifying the correctness of the implementation。 The tests are not reproduced here； but they are implemented in the sample source code。 I advise you to take a quick look at the tests to make sure you understand the individual pieces。 …………………………………………………………Page 70…………………………………………………………… 48 CH AP T E R 2 ■ L E A R N IN G AB OU T 。 N E T N U M B E R A N D V A L U E T Y P E S The Important Stuff to Remember In this chapter； you learned about developing a class library that is used to perform some calculations。 The following are the key points to remember： o Organization of your thoughts； projects； and features makes all the difference when writing software。 o When writing software； stay focused。 It is very easy to drift around in software development； because software lets you stray easily。 A successful developer will always be organized and focused。 o Software is designed using an architecture that could be implemented top…down or bottom…up。 o Within an architecture； individual pieces are called ponents； and they fit together to create