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Loop used to generate the index Function that determines whether or not the search can
series for the Connections array continue to the next Connections array element
Private Function FindNextLeg（ByVal returnArray As Node（）； _
ByVal count As Integer； _
ByVal destination As String； _
ByVal currNode As Node） As Boolean
For c1 As Integer = 0 To currNode。Connections。Length 1
If CanContinueSearch（returnArray； currNode。Connections（c1）） Then Assume that you can go to the
returnArray（count） = currNode。Connections（c1） connection； so add it to the
If currNode。Connections（c1）。CityName。pareTo（destination） = 0 Then
Return True found route array
Else
If FindNextLeg（returnArray； count ＋ 1； destination； _
currNode。Connections（c1）） Then If the current connection is the
Return True
End If end； stop searching down the
End If tree and return
End If Current connection is not the end； so go to
Next the connection and find another flight leg
Return False
End Function that will bring you to the destination
Figure 4…16。 FindNextLeg（） looks for the next leg in the journey。
The big idea here is to create a flight route by traveling the tree of connections in the hope
that one of the connections will cause you to end up at your end point。 Notice that for each leg；
the parameter count is incremented； so as you progress a level deeper in the tree； you assign
the city at the level to the found route array。
What makes this function tick is the decision code represented by an If code block。 The If
code block says； “If this decision test is true； then execute the code within the If block； other
wise； move to the code immediately after the If block。”
An If statement has the following form：
If ＇condition＇ Then
＇Do action＇
ElseIf ＇condition＇ Then
＇Do action＇
Else
＇Do action＇
End If
The statements If； ElseIf； and Else together represent one piece of logic （for example； if
this cannot happen； then test the ElseIf； if that cannot happen； then do the default in the Else）。
The statements after the first If are optional。
The ＇condition＇ must return a True or False value。 A True value means to execute the actions
within the block； and a False value means to try the next code statement。
The Else statement is a sort of default catchall that is executed if none of the other If state
ments prove to be true。
Here is an example of logic executed in an If statement：
If test1 Then
' Code1
ElseIf test2 Then
' Code2
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Else
' Code3
End If
' Code4
The following code steps are executed：
o If test1 is True； then execute Code1。 After executing Code1； execute Code4。
o If test1 is False； jump to ElseIf with test2。
o If test2 is True； then execute Code2。 After executing Code2； execute Code4。
o If test2 is False； jump to Else。
o Execute Code3。 After executing Code3； execute Code4。
Here is another example：
If test1 Then
' Code1
Else
' Code2
End If
' Code3
The executed code steps are as follows：
o If test1 is True； then execute Code1。 After executing Code1； execute Code3。
o If test1 is False； jump to Else。
o Execute Code2。 After executing Code2； execute Code3。
And here is one more example：
If test1 Then
' Code1
End If
If test2 Then
' Code2
Else
' Code3
End If
// Code4
The executed code steps are as follows：
o If test1 is True； then execute Code1。 After executing Code1； jump to If with test2。
o If test1 is False； jump to If with test2。
o If test2 is True； then execute Code2。 After executing Code2； execute Code4。
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o If test2 is False； jump to Else。
o Execute Code3。 After executing Code3； execute Code4。
The following code is illegal：
Else
' Code2
End If
' Code3
And this is also illegal：
ElseIf test2 Then
' Code2
Else
' Code3
End If
It is possible to have one If statement embedded within an Else； If； or ElseIf to create a
more plex multilevel decision tree。
The condition or test＇N ＇ variables are Boolean values that can contain True or False。 You
have already seen examples of these； like this：
If CanContinueSearch（returnArray； currNode。Connections（c1）） Then
The If statement says that if the method CanContinueSearch（） returns True； then execute
the contained code。
Here is another example of a condition：
If returnArray（c1） IsNot Nothing Then
This If statement says that if the array element returnArray＇（c1） does not have a value of
Nothing； then execute the contained code。
In both examples； either the method or parison must return a Boolean value。 If a Boolean
value is not returned； the Visual Basic piler will generate an error indicating that the code
does not result in a True or False value。
It is easy to see how a method can generate a True or False value； but the array element not
equal to Nothing statement is a bit more plicated。 The statement is an example of using
operators to perform a parison。 parisons test if things are equal to each other or not
equal to each other。 Table 4…2 shows the parison operators and what they mean。
Table 4…2。 parison Operators
Expression Description
a = b Does a equal b？
a b Does a not equal b？
a 》 b Is a greater than b？
a 《 b Is a less than b？
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Table 4…2。 parison Operat