ISOM3230 Business Applications Programming VBA Business Applications Implementing Formulas

Learning Outcomes   apply programming concepts to solve business problems   describe the logic and flows of given programs   predict the output of a program   write programs with common programming practices   identify and fix logical and run-time errors in programs 2

Outline 1. Understanding Mean and SD application 2. Problem #1: Wrapper Subroutines 3. Problem #2: Revised Data Types 4. Problem #3: Initialize an Array Simplified Macros Dynamic Array 5. Problem #4: Selection 6. Problem #5: Dynamic Size 3

3. Given Program 1. Mean & SD 2. Excel Worksheet 4 Prob. 3 Prob. 1 Prob. 2 Improvement Prob. 4 Implementing Formulas Sol. 3: Initialize array & Simplified Macros Sol. 1: Wrapper Sub. Sol. 2: Revised Data Types Sol. 4: Selection 4. Understanding Program Prob. 5Sol. 5: Dynamic Size

End 5

Business Applications – Implementing Formulas

Step 1: Mean and Standard Deviation  Mean (Average) is calculated using the following formula  Standard Deviation (SD) is calculated using the following formula

Step 1: Excel Worksheet  Excel worksheet as below

Public Sub Compute() Dim x(59) As Single Dim Average As Single Dim Std_Dev As Single Dim i As Integer For i = 1 To 59 x(i) = Sheets("ISOM3230").Cells(i + 1, 5) Next Average = Mean(59, x) Std_Dev = StdDev(59, x) Sheets("ISOM3230").Cells(61, 5) = Average Sheets("ISOM3230").Cells(62, 5) = Std_Dev End Sub Step 2: Given Program (1)  The following is the main program. General steps to process data in business applications: 1.Read data in and assign them to an array (determining the size of array and creating the array) 2.Process data 3.Present the results

Step 2: Given Program (2)  The following is the Mean function in VBA: Public Function Mean(ByVal n As Long, ByRef x() As Single) As Single Dim sum As Single Dim i As Integer sum = 0 For i = 1 To n sum = sum + x(i) Next Mean = sum / n End Function

Step 2: Given Program (3)  The following is the Standard Deviation function in VBA: Public Function StdDev(ByVal n As Long, ByRef x() As Single) As Single Dim i As Integer Dim avg As Single, SumSq As Single SumSq = 0 avg = Mean(n, x) For i = 1 To n SumSq = SumSq + (x(i) - avg) ^ 2 Next StdDev = Sqr(SumSq / (n - 1)) End Function

 When the Text Box is clicked, the procedure Compute() executes and calculates Mean and Standard Deviation by calling functions Mean and StdDev. Step 3: Understanding the program – Excel controls

Step 3: Understanding the program – Main program and the two functions

Is it the End? No! We need improvement

Problem 1  In the original program, it must calculate both mean and standard deviation together, but not one of them. However, there are functions in the VBA module and that cannot be assigned to any Excel controls. Why?  Solution Make wrapper subroutines to both Mean and StdDev. A wrapper is simply a subroutine in which it calls a particular function with some predefined settings Make wrapper subroutines to both Mean and StdDev. A wrapper is simply a subroutine in which it calls a particular function with some predefined settings Assign both wrapper subroutines into remaining Excel controls called Average and StdDev Assign both wrapper subroutines into remaining Excel controls called Average and StdDev 15

Solution 1: Wrapper Subroutines 16 Public Function Mean(ByVal n As Long, ByRef x() As Single) As Single... End Function Public Function StdDev(ByVal n As Long, ByRef x() As Single) As Single... End Function They are functions and cannot be assigned as macros program Public Sub Average() Dim x(59) As Single Dim i As Integer For i = 1 To 59 x(i) = Sheets("ISOM3230").Cells(i + 1, 5) Next Sheets("ISOM3230").Cells(61, 5) = Mean(59, x) End Sub Wrapper subroutine for Mean function

Problem 2  As you know, average and standard deviation are the basic Excel built-in functions. And now, we intend to verify the correctness of our program  Insert “=AVERAGE(E2:E60)” to Cell F61  Insert “=STDEV(E2:E60)” to Cell F62  Expand the width of the column F so that we can see all digits  From the Excel functions, they generate the results that are a little difference from ours. But, both Excel and our functions apply the same equations. Why?  Solution Replace all variables from Single to Double Replace all variables from Single to Double 17

Solution 2: Revised Data Types 18 Public Function StdDev(ByVal k As Long, ByRef Arr() As Single) As Single Dim i As Integer Dim avg As Single, SumSq As Single avg = Mean(k, Arr) For i = 1 To k SumSq = SumSq + (Arr(i) - avg) ^ 2 Next StdDev = Sqr(SumSq / (k - 1)) End Function Solution - change all single variables into double Using single precision may not be appropriate that introduces incorrect financial values Public Function StdDev(ByVal k As Long, ByRef Arr() As Double) As Double Dim i As Integer Dim avg As Double, SumSq As Double avg = Mean(k, Arr) For i = 1 To k SumSq = SumSq + (Arr(i) - avg) ^ 2 Next StdDev = Sqr(SumSq / (k - 1)) End Function

Problem 3  In most of times, a professional programmer cannot guarantee number of user inputs (input data) to be captured from an end user  Therefore, we cannot assume the number of elements in the current program is 59 always What if the end user inserts one or two elements instead? What if the end user inserts one or two elements instead? The program must be modified in order to handle the new data set The program must be modified in order to handle the new data set  We also cannot assume our end users have VBA programming knowledge in order to use the program  So, how can we solve this problem?  Solution Change from the fixed-size array into a dynamic-size array using ReDim Change from the fixed-size array into a dynamic-size array using ReDim Use IsEmpty() to detect the end of a data set Use IsEmpty() to detect the end of a data set 19

Solution 3: Initialize an Array 20 Public Sub InitializeArray(ByRef x() As Double) Dim i As Integer i = 1 Do Until IsEmpty(Sheets("ISOM3230").Cells(i + 1, 5)) i = i + 1 Loop ReDim x(1 To i - 1) i = 1 Do Until IsEmpty(Sheets("ISOM3230").Cells(i + 1, 5)) x(i) = Sheets("ISOM3230").Cells(i + 1, 5) i = i + 1 Loop End Sub Solution: Create a separate subroutine to initialize an array Apply IsEmpty to determine whether a cell is empty

Solution 3: Initialize an Array 21 Public Sub InitializeArray(ByRef x() As Double) Dim i As Integer i = 1 Do Until IsEmpty(Sheets("ISOM3230").Cells(i + 1, 5)) i = i + 1 Loop ReDim x(1 To i - 1) For i = LBound(x) To UBound(x) x(i) = CDbl(Sheets("ISOM3230").Cells(i + 1, 5).Value) Next End Sub Revised Solution: Create a separate subroutine to initialize an array Use For-Next Loop when the array size is determined Type Conversion

Solution 3: Simplified Macros 22 Public Sub Compute() Dim x(59) As Double Dim Average As Double Dim Std_Dev As Double Dim i As Integer For i = 1 To 59 x(i) = Sheets("ISOM3230").Cells(i + 1, 5) Next Average = Mean(59, x) Std_Dev = StdDev(59, x) Sheets("ISOM3230").Cells(61, 5) = Average Sheets("ISOM3230").Cells(62, 5) = Std_Dev End Sub Public Sub Compute() Dim x() As Double InitializeArray x Sheets("ISOM3230").Range("AVG") = Mean(x) Sheets("ISOM3230").Range("STDEV") = StdDev(x) End Sub Solution: In Excel file, we must create an empty cell to notify that is the end of records Similar changes to Average and SD functions Make the array to become dynamic and remove redundant variables Create Named Range for particular data cells

Solution 3: Dynamic Array 23 Public Function Mean(ByVal n As Long, ByRef x() _ As Double) As Double Dim sum As Double Dim i As Integer sum = 0 For i = 1 To n sum = sum + x(i) Next i Mean = sum / n End Function Public Function Mean(ByRef x() As Double) As Double Dim sum As Double Dim i As Integer sum = 0 For i = LBound(x) To UBound(x) sum = sum + x(i) Next i Mean = sum / UBound(x) End Function Solution: Remove the variable n, and use LBound() and UBound() instead Apply similar changes to StdDev too Make the program to be more generic

Problem 4  Until now, an end-user can easily calculate the mean and standard deviation (SD) from all input data in the worksheet  Sometimes, not all values are required as input data. In this case, the user must select relative cells together and calculate new average and SD again  In the original design, all data cells are connected together and their values are transferred to an array. Now, we need a special mechanism to capture user selection, and copy each individual cell to an array; Then, apply the particular function. i.e. Average and SD  How? 24

From Selection to Array Dim x() As Double Dim r As Range Dim i As Integer i = 1 ReDim x(1 To Selection.Count) For Each r In Selection x(i) = CDbl(r.Value) i = i + 1 Next... Solution x

Solution 4: Selection 26 Public Sub Cal_Average() Dim x() As Double Dim r As Range Dim i As Integer i = 1 ReDim x(1 To Selection.Count) For Each r In Selection x(i) = CDbl(r.Value) i = i + 1 Next MsgBox Mean(x) End Sub Public Sub Cal_SD() Dim x() As Double Dim r As Range Dim i As Integer i = 1 ReDim x(1 To Selection.Count) For Each r In Selection x(i) = CDbl(r.Value) i = i + 1 Next MsgBox StdDev(x) End Sub

Problem 5  There is another way to choose the calculated data, which is using Selection  By using: Range("E2").Select Range(Selection, Selection.End(xlDown)).Select  You may choose a rectangular interconnected data cells  How to modify? (Hint: Only modify the InitializeArray subroutine) 27

Solution 5: Dynamic Size 28 Public Sub InitializeArray(ByRef x() As Double) Dim i As Integer i = 1 Do Until IsEmpty(Sheets("ISOM3230").Cells(i + 1, 5)) i = i + 1 Loop ReDim x(1 To i - 1) For i = LBound(x) To UBound(x) x(i) = CDbl(Sheets("ISOM3230").Cells(i + 1, 5).Value) Next End Sub Public Sub InitializeArray(ByRef x() As Double) Dim i As Integer Dim r As Range Range("E2").Select Range(Selection, Selection.End(xlDown)).Select ReDim x(1 To Selection.Count) i = 1 For Each r In Selection x(i) = CDbl(r.Value) i = i + 1 Next End Sub