Effective Decision Making
IF Else And Or Not If
The "If" Function in
VBA for Excel is very similar to the "IF" function used in a Worksheet
formula. It will return either True or False
and it does no more or less than this. As with the "IF" used in
the Worksheet formula the "If" in VBA can take up to two arguments, one for True
and one for False. So the syntax for the "If" is simply:
If <Condition to check>
Is True Then
'Do one
thing
Else
'Do another
thing
End If
So this same Function
used in a realistic way could be
Sub
TheIfFunction()
If Range("A1").Value > 100
Then
Range("B1").Value = 50 +
Range("A1").Value
Else
Range("B1").Value = 100
End
If
End Sub
This is telling Excel that If the Value of A1 is greater than 100 (True) then change the Value of B1 to the Value of A1 plus another 50, Else (False) changes the Value of B1 to 100. This would be the "If" Function used in it's simplest form. Once Excel encounters the "If" Function it will check the Value of A1, if the value is greater than 100 it will enter into the True argument:
Range("B1").Value = 50 + Range("A1").Value
From there it will Exit the "If" or in other words it will skip the False argument:
Range("B1").Value = 100
But lets assume we wanted
Excel to check if Range A1 is equal to 500 first and only go on if it's not
(False), to achieve this we would need to extend the "If" so it will possibly
check two conditions before exiting the remainder of the "If". This is how we
could do this:
Sub
TheIfFunction()
If Range("A1").Value = 500 Then
Range("C1").Value = 100 -
Range("A1").Value
ElseIf Range("A1").Value > 100 Then
Range("C1").Value = 50 + Range("A1").Value
Else
Range("B1").Value =
100
End
If
End
Sub
This Function is saying that, If Range A1 is equal to 500 (True) then:
Range("C1").Value = 100 - Range("A1").Value
But If Range A1 is NOT equal to 500 then check another condition, which is:
ElseIf Range("A1").Value > 100 Then
If this is True then:
Range("C1").Value = 50 + Range("A1").Value
Finally if neither of these conditions are True then:
Range("B1").Value = 100
We could in theory keep adding an unlimited
amount of "ElseIf" Functions to check for multiple conditions. The problem with
this is that our "If" Function would become almost impossible to read and more
importantly, decipher. I will show you a much better method soon for checking
multiple conditions, but for now we will stick with the "If" Function.
There are two other common Keywords used in conjunction with the "If" Function, they are the "And" and the "Or" Operators. We will look first at the "And" operator.
The "And" operator is use to perform a
conjunction of two conditions. Whenever we use the "And" operator with the "If"
Function it will only ever return True if BOTH conditions are met
(True and True). So if we used the "If" combined with the "And"
like below:
Sub
TheIfAndFunction()
If Range("A1").Value > 100 And
Range("A1").Value < 500 Then
Range("B1").Value =
Range("A1").Value
End
If
End
Sub
This would tell Excel that If Range A1 is between 100 and 500 (True) then make:
Range("B1").Value = Range("A1").Value
If Range A1 is Not between 100 and 500 do
nothing. We could again add an unlimited amount of "And" operators all checking
different conditions, but again this would become very hard to decipher and is
also not very efficient.
The other common Operator used with the "If"
Function is the "Or" Operator. This will check if one of two conditions
are True and return True if only one of them is met (True and
False) or (False and True). Below is an example of
this:
Sub
TheIfOrFunction()
If
Range("A1").Value = 100 Or Range("A1").Value = 500 Then
Range("B1").Value = Range("A1").Value
End
If
End
Sub
This "If" Statement will return True If Range
A1 is equal to 100 OR If Range A1 is equal to 500 any other condition
would return False and do nothing.
These two Operators are by far the most
commonly used Operators used with the "If" Function.
So the "If" Function can be used to determine whether a Function is either True or False and act accordingly. Combining it with the Operators "And" and "Or", can extend it's functionality. In all the above examples the "If" Functions use the "End If" Keywords. These simply let Excel know that the "If" Function has finished. If we restrict our "If" Function to one line of code only we can omit the "End If" completely, like below:
Sub
NoEndIf()
If
Range("A1").Value = 100 Then Range("B1").Value =
20
End
Sub
This can at times make your code slightly
easier to read. There is no performance gain by doing the "If" Function this
way, so don't get caught in the trap of always trying to fit your "If" Function
onto one line. If by doing so you cannot read the entire line without scrolling
to the right use two or more lines with the "End
If".
There is one other way of evaluating a
condition with the "If" and that is called the "Iif". I will only show you this
because it exists, but I do not recommend using it for two
reasons.
It's slightly
slower
It has no advantage over the "If
Else"
The syntax for IIf is:
To use this in a similar way as the "If", we
could use:
Sub
TheIIf()
IIf
Range("A1").Value = 100, Range("B1").Value = 20, Range("B1") =
50
End
Sub
But as I have said I would avoid using this as it holds no advantage.
The other operator we can use with the "If" Statement is the "Not" Statement. This is used to reverse the "If" Statement
Sub IfNot()
If Not Range("A1") = 100 Then
MsgBox "Not 100", vbInformation, "OzGrid Example"
End If
End Sub
In the example above we have used the "Not" statement to reverse the logic of the "If" statement. By this I mean we have told our "If" statement to return True if Range A1 is not equal to 100
Select
Case
The other method of checking for single or multiple conditions is the Select Case Function. This is another method used for decision making based on a condition or criteria. It, in my opinion, is much better than If etc. This has the syntax
Select Case <Expression to
test>
Case
<Test1>
Do
something
Case
<Test2>
Do
something
Case
Else
Do something else
End
Select
As you can see the "Select Case"
Function is very similar to the "If" Function in that it will only perform some
action if a condition is met. While this may seem no better than the "If"
Function I feel that it is a MUCH better choice than the "If"
Function If more than one condition or expression needs to be tested. Not only
is it more efficient but it has a
much better structure than the "If" Function. This means it is far easier to
read or decipher and believe me you WILL need to go back through your
written code frequently to find out a problem (De-bug). While these two reasons
alone are enough for me, there is another and that is it has FAR
more flexibility. We will first look at the "Select Case" Function in
it's simplest form
Sub
TheSelectCase()
Select Case Range("A1").Value
Case
100
Range("B1") = 50
End
Select
End
Sub
Sub TheSelectCase()
Select Case
Range("A1").Value
Case
100
Range("B1").Value =
50
Case
150
Range("B1").Value = 40
Case
200
Range("B1").Value = 30
Case
350
Range("B1").Value = 20
Case
400
Range("B1").Value =
10
End
Select
End Sub
Sub
TheSelectCase()
Select Case
Range("A1").Value
Case
100
Range("B1").Value = 50
Case
150
Range("B1").Value = 40
Case
200
Range("B1").Value = 30
Case
350
Range("B1").Value = 20
Case
400
Range("B1").Value = 10
Case
Else
Range("B1").Value = 0
End
Select
End
Sub
So If the Value of Range A1 is NOT 100,150,200,350 or 400 then place a Value of 0 (zero) in Range B1. Now while this demonstrates how we can check multiple conditions with the "Select Case" Function, what if we want to perform some action If the Range A1 is equal to any one of the Values 100,150,200,350 or 400. If this is the case (no pun indented) we could use:
Select Case
Range("A1").Value
Case 100, 150,
200, 350, 400
Range("B1").Value = Range("A1").Value
Case Else
Range("B1").Value = 0
End
Select
End
Sub
I don't believe anybody could argue against this being a far better structure than an "If" Function with multiple "Or" Operators.
We used the "If" Function combined with the
"And" operator above to demonstrate how to let Excel know if the Value of Range
A1 is between two numbers. We can do this also with the "Select Case" Function
with even greater ease:
Sub
TheSelectCase()
Select Case Range("A1").Value
Case
100 To 500
Range("B1").Value = Range("A1").Value
Case
Else
Range("B1").Value = 0
End
Select
End
Sub
Sub
TheSelectCase()
Select Case Range("A1").Value
Case
100 To 500, 600 To 1100, 1200 To 2000
Range("B1").Value = Range("A1").Value
Case
Else
Range("B1").Value = 0
End
Select
End
Sub
Sub
TheSelectCase()
Select Case
Range("A1").Text
Case
"Aardvark" To "Elephant"
Range("B1").Value = "it's
between"
Case
Else
Range("B1").Value = "it's not between"
End
Select
End
Sub
So as you can see there are many ways within VBA for Excel we can use to evaluate and determine a Value or Text. You will find yourself using the "If" and "Select Case" Functions quite frequently and as I have already indicated, the Select Case is often a much better option.
Excel and Dates
Dates are frequently used in Excel and in
VBA for Excel, also for this reason I believe it is an important aspect to at
least know the fundamentals of. The text below is from the Excel help file
and explains how Excel sees or interprets
Dates.
How Microsoft Excel
performs date and time calculations
Microsoft Excel stores
dates as sequential numbers known as serial values and stores times as decimal
fractions because time is considered a portion of a day. Dates and times are
values and therefore can be added, subtracted, and included in other
calculations. For example, to determine the difference between two dates, you
can subtract one date from the other. You can view a date or time as a serial
number or a decimal fraction by changing the format of the cell that contains
the date or time to General format.
Microsoft Excel supports
two date systems: the 1900 and 1904 date systems. The default date system for
Microsoft Excel 97 for Windows is 1900. To change to the 1904 date system, click
Options on the Tools menu, click the Calculation tab, and then select the 1904
date system check box.
Note: When you enter a date in Microsoft
Excel 97, or later and you enter only two digits for the year, Microsoft Excel
enters the year as follows:
The years 2000 through 2029 if you type 00 through 29 for the year. For example, if you type 5/28/19, Microsoft Excel assumes the date is May 28, 2019.
The years 1930 through 1999 if you
type 30 through 99 for the year. For example, if you type 5/28/91, Microsoft
Excel assumes the date is May 28, 1991.
End of Excel
Help
Using Dates in VBA for Excel offers a lot more
flexibility, but also has more pitfalls that can catch the uninformed out. This
is due mainly to the fact that Excel is used globally and there is more than one
Date system. We will look at the two most common and that is the American
(Month-Day-Year) and the European (Day-Month-Year). This issue will be nearly
non-existent if you know for a fact that the code written in VBA will only be
used on one Date system. But should you write a Procedure that will be used by
more than one Date system, problems can arise. In today's market it is not
unusual for say an English company to have to deal with a Spreadsheet that uses
the American Date System or an vice versa. You can imagine the problems that
could arise if the Dates you insert into a Spreadsheet via VBA are assumed to be
of the American Date System when in reality they are of the European Date
System. Fortunately the makers of VBA for Excel have realised this and provided
a universal Function to eliminate possible disasters. I would urge you to again
form a good habit early and incorporate it whenever dealing with Dates. The Function is called the "DateSerial"
Function. It has the Syntax:
Sub
UniversalDate()
Dim dTheDate
As Date
dTheDate = DateSerial(2001, 6,
5)
Range("A1").Value =
dTheDate
End
Sub
Using this Function will eliminate any possible
confusion of the Date System used. Whenever you use or Parse a Date to a
Variable or Range you must enclose it within the # (Hash signs) eg;
If you try and type this into Excel exactly as
is you will see that Excel will automatically change it to the American Date
System whether you want it to or not. In other words it will end up
like:
dTheDate =
#5/22/01#
You may or may not notice the Month and Day
being switched if you are happily typing away. But worse than this is if you
use:
Sub
UniversalDate()
Dim dTheDate
As Date
dTheDate =
#10/12/01#
Range("A1").Value =
dTheDate
End
Sub
….and you are used to the European
Date System you would assume the Date going into Range A1 is the 10th Day of
December, 2001. Guess what, WRONG! You will actually end up with the
12th Day of October, 2001 instead.
Of course if we aware of this and we have formed the good habit of using the
"DateSerial" Function for all Dates no such problem will arise. Eg;
Sub
UniversalDate()
Dim dTheDate
As Date
dTheDate =
DateSerial(2001, 12, 10)
Range("A1").Value = dTheDate
End
Sub
I hope this stresses the importance of using the DateSerial Function whenever you are working with Dates in Excel
Date
Functions
Now that we realise the possible pitfalls of
working with Dates I will show you some handy Functions you can use in Excel
when working with Dates.
The first one is the "Date" Function,
this will return the current systems Date. As it is returning the current system
Date, it will use the Date System of the PC it is run
on.
Next we have the "DateValue" Function.
This is the same as the Worksheet Formula DATEVALUE in that it will
return a real Date from a String Date, eg;
Sub
UniversalDate()
Dim dTheDate
As Date
dTheDate =
DateValue("12/May/01")
Range("A1").Value =
dTheDate
End
Sub
This will Parse the Date Value for 12th day of May, 2001 to our Date
Variable "dTheDate", which in turn will place it in cell A1. You may also have
noticed that we could also use the
"DateValue" function to prevent mishaps when working with Dates. There is no
reason why you couldn't and it won't matter so long as you use one or the
other.
To add a specified period of time to a Date we
could use the "DateAdd" Function, this has the
Syntax:
Sub
DateAddFunction()
Dim dTheDate
As Date
dTheDate = DateAdd("d", 45,
"18/may/2001")
Range("A1").Value =
dTheDate
End
Sub
yyyy
Year
q Quarter
m
Month
y
Day of year
d
Day
w Weekday
ww
Week
h
Hour
n
Minute
s
Second
There are many other types of Functions that can be used with Dates but as this is level 1 VBA I won't confuse the issue by going into them all. The two most important points to remember when working with Dates are How Microsoft Excel performs date and time calculations and being aware of the International issues associated with Dates.
As always, if you have any question's on this lesson or past lessons, please feel free to contact me.
©2002 ozgrid - microsoftexceltraining - David & Raina Hawley. All right reserved