Class 3 Programming in Visual Basic

Class Objectives Learn about input/output Learn about strings Learn about subroutines Learn about arrays Learn about Boolean operations

Addressing Spreadsheet Cells A B C D Rows Columns Cell C2 A1 Reference Style

Addressing Spreadsheet Cells A B C D Rows Cell (2, 3) R1C1 Reference Style row, column Columns

VBA Interaction with Excel Excel VBA Function 0, 1, 2, 3 … numbers 1 number Excel VBA Subroutine 0, 1, 2, 3 … numbers 1, 2, 3 … numbers Our focus today

Strings Sub string_demo() Cells(10, 1) = "First" Cells(10, 2) = "Second" Cells(10, 3) = "Third" End Sub Using the VBA editor, enter the following program… While in VBA editor, press F5 to run Subroutine Name Strings in double quotes No arguments passed

Results

Sample Subroutine with Calculation Sub sum_and_product_of_five_numbers() 'This program gives the sum and product of ' five numbers located in Cells B1 to B5 Dim row As Integer Dim sum, product As Double sum = 0 product = 1 For row = 1 To 5 sum = sum + Cells( row, 2) product = product * Cells( row, 2) Next row Cells(6, 1) = "sum" Cells(7, 1) = "product" Cells(6, 2) = sum Cells(7, 2) = product End Sub Subroutine name Comment Declare variables Initialize variables Start loop Input and calculate End loop Output End In VBA editor, enter this program.

Example (con’t) Enter five numbers in cells B1 to B5

Example (con’t) 1.Press Alt+F8 2.Select 3.Press Run

Result

An easier way to execute a subroutine  You can link a subroutine to a keyboard control character.  Assignment is made under Options in the Macro dialog box.

Using Macro Options  Under Options, fill in a letter next to “ctrl+” and the selected macro can be executed by pressing that key combination.  Be careful. If you choose a character that is a standard Windows function (e.g., ctrl+c), VBA will overwrite the Windows function with your macro.

Arrays Dim list (5) as integer Example Indices Default: Index starts with zero Numbers stored in array

Arrays Dim list (1 to 5) as integer Indices Override: Index starts with one Numbers stored in array Example 2

Arrays Dim list (1 to 5, 1 to 2) as integer Row Indices 1 2 Column Indices This is a two-dimensional array. Up to 60 dimensions are allowed. Example 3

Sample Program Sub array_demo() Dim list(1 To 5) As Integer Dim i As Integer Dim sum As Integer sum = 0 i = 1 list(1) = 1 list(2) = 4 list(3) = 9 list(4) = 16 list(5) = 25 Do While sum < 16 sum = sum + list( i) i = i + 1 Loop Cells(15, 1) = "sum =" Cells(15, 2) = sum End Sub Title Declare variables Initialize variables Start loop Calculate End loop Output End Enter and run this program.

Results Sub array_demo() Dim list(1 To 5) As Integer Dim i As Integer Dim sum As Integer sum = 0 i = 1 list(1) = 1 list(2) = 4 list(3) = 9 list(4) = 16 list(5) = 25 Do While sum < 16 sum = sum + list( i) i = i + 1 Loop Cells(15, 1) = "sum =" Cells(15, 2) = sum End Sub

Boolean Operations Truth Tables A B Y And A B Y Or A Y Not result = expression1 Or expression2 result = Not expression result = expression1 And expression2 0 = false 1 = true Y A B

Example Program Option Explicit Sub Boolean_test() Dim truth As Boolean Dim a, b As Integer a = 1 b = 2 truth = False If a = 1 And b = 2 Then truth = True End If Cells(1, 1) = truth End Sub Title Declare variables Initialize Boolean operation Assign Output End Enter and run this program. To see what happens, play with various Boolean operators, and different initial values of a and b.

Function Exercise  The value of  (the ratio of a circle’s circumference to its diameter) has been estimated for about 4000 years.  Several methods for calculating  are presented in the Math Supplement (pages 8-10).  Excel’s built in function for  is only accurate to 14 decimal places (van Rooman did better in 1593).  As a team, pick ~4 (1 per team member) of the various methods used to estimate  using infinite series (avoid Methods a, c, e and k).  Program your function to calculate the first 50 terms, or stop when the value does not change by more than

Subroutine Exercise  Convert your function into a subroutine.  The subroutine should title Column A as  and Column B as that is, the change in  from the previous iteration.  Then beginning in Cells A2 and B2 and going down, output the successive terms of .  Stop the iteration after the first 200 terms, or if an additional term does not change the value of  by more than  For each method selected by your teammates, compare the rate that they converge to an accurate value of 