If Condition1 Then Statement1 ElseIf Condition2 Then Statement2 ElseIf Conditionk Then Statementk End If
The program will first examine Condition1. If
Condition1 is true, the program will execute Statment1 and stop
examining conditions. If Condition1 is false, the program will
examine Condition2 and act accordingly. Whenever a condition is
false, the program will continue examining the conditions until it
finds one that is true. Once a true condition has been found and its statement
executed, the program will terminate the conditional examination at
End If. Here is an example:
Sub Exercise()
Dim MemberAge As Byte
MemberAge = 32
If MemberAge <= 18 Then
MsgBox ("Membership: " & "Teen")
ElseIf MemberAge < 55 Then
MsgBox ("Membership: " & "Adult")
End If
End Sub
This would produce:
There is still a possibility that none of the
stated conditions be true. In this case, you should provide a
"catch all" condition. This is done with a last Else
section. The Else section must be the last in the list of
conditions and would act if none of the primary conditions is true.
The formula to use would be:
If Condition1 Then Statement1 ElseIf Condition2 Then Statement2 ElseIf Conditionk Then Statementk Else CatchAllStatement End If
Here is an example:
Sub Exercise()
Dim MemberAge As Byte
MemberAge = 65
If MemberAge <= 18 Then
MsgBox ("Membership: " & "Teen")
ElseIf MemberAge < 55 Then
MsgBox ("Membership: " & "Adult")
Else
MsgBox ("Membership: " & "Senior")
End If
End Sub
This would produce:
As introduced in previous lessons, we know that a
function is used to perform a
specific assignment and produce a result. Here is an example:
Private Function SetMembershipLevel$()
Dim MemberAge%
MemberAge% = InputBox("Enter the Member's Age")
SetMembershipLevel$ = ""
End Function
When performing its assignment, a function can encounter
different situations, some of which would need to be checked for
truthfulness or negation. This means that conditional statements can
assist a procedure with its assignment.
A function is meant to
return a value. Sometimes, it will perform some tasks whose results
would lead to different results. A function can return only one value (we
saw that, by passing arguments by reference, you can make a procedure
return more than one value) but you can make it render a result
depending on a particular behavior. If a function is requesting an answer
from the user, since the user can provide different answers, you can treat
each result differently. Consider the following function:
Private Function SetMembershipLevel$()
Dim MemberAge%
MemberAge% = InputBox("Enter the Member's Age")
If MemberAge% < 18 Then
SetMembershipLevel$ = "Teen"
ElseIf MemberAge% < 55 Then
SetMembershipLevel$ = "Adult"
End If
End Function
Sub Exercise()
Dim Membership$
MsgBox ("Membership: " & Membership$)
End Sub
At first glance, this function looks fine. The user is asked
to provide a number. If the user enters a number less than 18 (excluded), the
function returns Teen. Here is an example of running the program:
 
If the user provides a number between 18 (included) and 55, the
function returns the Adult. Here is another example of running the
program:
 
What if there is an answer that does not fit those we are
expecting? The values that we have returned in the function conform only
to the conditional statements and not to the function. Remember that in If
Condidion Statement, the Statement executes only
if the Condition is true. Here is what will happen. If the
user
enters a number higher than 55 (excluded), the function will not
execute any of the returned statements. This means that the execution
will reach the
End Function line
without encountering a return value. This also indicates to the compiler that
you wrote a function that is supposed to return a value, but by the
end of the method, it didn't return a value. Here is another example of
running the program:
 
To solve this problem, you have various alternatives. If the
function uses an If...Then condition, you can create an Else section that
embraces any value other than those validated previously. Here is an example:
Private Function SetMembershipLevel$()
Dim MemberAge%
MemberAge% = InputBox("Enter the Member's Age")
If MemberAge% < 18 Then
SetMembershipLevel$ = "Teen"
ElseIf MemberAge% < 55 Then
SetMembershipLevel$ = "Adult"
Else
SetMembershipLevel$ = "Senior"
End If
End Function
Sub Exercise()
Dim Membership$
Membership$ = SetMembershipLevel$()
MsgBox ("Membership: " & Membership$)
End Sub
This time, the Else condition would execute if no
value applies to the If or ElseIf conditions and the compiler
would not produce a warning. Here is another example of running the program:
 
An alternative is to provide a last return value just before
the End Function line. In this case, if
the execution reaches the end of the function, it would still return
something but you would know what it returns. This would be done as follows:
Private Function SetMembershipLevel$()
Dim MemberAge%
MemberAge% = InputBox("Enter the Member's Age")
If MemberAge% < 18 Then
SetMembershipLevel$ = "Teen"
ElseIf MemberAge% < 55 Then
SetMembershipLevel$ = "Adult"
End If
SetMembershipLevel$ = "Senior"
End Function
If the function uses an If condition, both implementations
would produce the same result.
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Practical Learning: Introducing
Data Entry
The IIf()
function can also be used in place of an If...Then...ElseIf
scenario. When the function is called, the Expression is
checked. As we saw already, if the expression is true, the function returns the
value of the TruePart argument and ignores the last argument. To use this
function as an alternative to If...Then...ElseIf statement, if the
expression is false, instead of immediately returning the value of the FalsePart
argument, you can translate that part into a new IIf function. The pseudo-syntax
would become:
Public Function IIf( _
ByVal Expression As Boolean, _
ByVal TruePart As Object, _
Public Function IIf( _
ByVal Expression As Boolean, _
ByVal TruePart As Object, _
ByVal FalsePart As Object _
) As Object
) As Object
In this case, if the expression is false, the function
returns the TruePart and stops. If the expression is false, the compiler
accesses the internal IIf function and applies the same scenario. Here is
example:
Sub Exercise()
Dim MemberAge As Byte
Dim MembershipCategory As String
MemberAge = 74
MembershipCategory = _
IIf(MemberAge <= 18, "Teen", IIf(MemberAge < 55, "Adult", "Senior"))
MsgBox ("Membership: " & MembershipCategory)
End Sub
We saw that in an If...Then...ElseIf statement you
can add as many ElseIf conditions as you want. In the same, you can call
as many IIf functions in the subsequent FalsePart sections as you
judge necessary:
Public Function IIf( _ ByVal Expression As Boolean, _ ByVal TruePart As Object, _ Public Function IIf( _ ByVal Expression As Boolean, _ ByVal TruePart As Object, _ Public Function IIf( _ ByVal Expression As Boolean, _ ByVal TruePart As Object, _ Public Function IIf( _ ByVal Expression As Boolean, _ ByVal TruePart As Object, _ ByVal FalsePart As Object _ ) As Object ) As Object ) As Object ) As Object
As we have seen so far, the Choose function takes a
list of arguments. To use it as an alternative to the If...Then...ElseIf...ElseIf
condition, you can pass as many values as you judge necessary for the second
argument. The index of the first member of the second argument would be 1. The
index of the second member of the second argument would be 2, and so on. When
the function is called, it would first get the value of the first argument, then
it would check the indexes of the available members of the second argument. The
member whose index matches the first argument would be executed. Here is an
example:
Sub Exercise()
Dim Status As Byte, EmploymentStatus As String
Status = 3
EmploymentStatus = Choose(Status, _
"Full Time", _
"Part Time", _
"Contractor", _
"Seasonal")
MsgBox ("Employment Status: " & EmploymentStatus)
End Sub
This would produce:
So far, we have used only strings for the values of the
second argument of the Choose() function. In reality, the values of the
second argument can be almost anything. One value can be a constant. Another
value can be a string. Yet another value can come from calling a function. Here
is an example:
Private Function ShowContractors$() ShowContractors$ = "=-= List of Contractors =-=" & vbCrLf & _ "Martin Samson" & vbCrLf & _ "Geneviève Lam" & vbCrLf & _ "Frank Viel" & vbCrLf & _ "Henry Rickson" & vbCrLf & _ "Samuel Lott" End Function Sub Exercise() Dim Status As Byte, Result$ Status = 3 Result = Choose(Status, _ "Employment Status: Full Time", _ "Employment Status: Part Time", _ ShowContractors, _ "Seasonal Employment") MsgBox (Result) End Sub
This would produce:
The values of the second argument can even be of different
types.
The Switch() function is a prime alternative to the If...Then...ElseIf...ElseIf
condition. The argument to this function is passed as a list of values. As seen
previously, each value is passed as a combination of two values:
ConditionXToCheck, StatementX
As the function is accessed, the compiler checks each
condition. If a condition X is true, its statement is executed. If a condition Y
is false, the compiler skips it. You can provide as many of these combinations
as you want. Here is an
example:
Private Enum EmploymentStatus
FullTime
PartTime
Contractor
Seasonal
End Enum
Sub Exercise()
Dim Status As EmploymentStatus
Dim Result As String
Status = EmploymentStatus.Contractor
Result = "Unknown"
Result = Switch(Status = EmploymentStatus.FullTime, "Full Time", _
Status = EmploymentStatus.PartTime, "Part Time", _
Status = EmploymentStatus.Contractor, "Contractor", _
Status = EmploymentStatus.Seasonal, "Seasonal")
MsgBox ("Employment Status: " & Result)
End Sub
This would produce:
In a true If...Then...ElseIf...ElseIf condition, we
saw that there is a possibility that none of the conditions would fit, in which
case you can add a last Else statement. The Switch() function also
supports this situation if you are using a number, a character, or a string. To
provide this last alternative, instead of a ConditionXToCheck
expressionk, enter True, and include the necessary statement. Here is an
example:
Sub Exercise()
Dim Status As Byte
Dim Result As String
Status = 12
Result = Switch(Status = 1, "Full Time", _
Status = 2, "Part Time", _
Status = 3, "Contractor", _
Status = 4, "Seasonal", _
True, "Unknown")
MsgBox ("Employment Status: " & Result)
End Sub
This would produce:
Remember that you can also use True with a character. Here
is an example:
Sub Exercise()
Dim Gender As String
Dim Result As String
Gender = "H"
Result = Switch(Gender = "f", "Female", _
Gender = "F", "Female", _
Gender = "m", "Male", _
Gender = "M", "Male", _
True, "Unknown")
MsgBox ("Gender: " & Result)
End Sub
This would produce:
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