1. Programming in Visual Basic
Class 2
Programming in Visual Basic

2. Class Objectives
Recognize when programming is required to solve a problem
Understand basic structure of a program
Understand function vs. subroutine
Know how to create a program
Know rules for naming variables
Know precedence of arithmetic and comparison operators
Understand integer vs real number

3. Class Objectives (con’t)
Understand comments
Know what to do if a line is too long
Know how to protect against spelling errors
Selection structures: If, If-Else, If-ElseIf
Repetition structures: Do Until, For

4. What is a program?
Program – An algorithm implemented within a computer.

5. When do you use a program?
Spreadsheets can perform about 95% of the computing tasks; however, they are not suitable for the following:
Highly repetitive tasks
Decision making

6. What are some programming languages?
Basic
Cobal
Fortran
Pascal
Ada
Java C
LISP
We will use Visual Basic for Applications (VBA). MatLab?

7. What is Visual Basic for Applications (VBA)?
It is a version of Visual Basic that is embedded within Excel.

8. Why are we learning VBA, rather than another programming language?
Simple
Easy to learn
Quickly learned
Capitalizes on your knowledge of Excel

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

10. Sample Function Function name Identifies program as a
Numbers passed into
function through arguments
Function adder( a, b)
adder = a b
End Function
Action taken
by the function
Identifies the end of the function
The single number is returned through the function name

11. Creating a VBA program

12. Step 1 – Open Excel

13. Step 2 – Save as…
Save as …
Example_1

14. Step 3 – Open VBA Editor
Press…
Alt F11

15. Step 4 – Identify where to file your program
Left-click
here

16. Step 5 – Insert module
Left click
Insert
Left click
Module

17. A blank form will appear
This is where the program goes

18. Step 6 – Type in program
Here is the program

19. Use your program

20. Step 1 – Go to Excel spreadsheet
Left click
Excel button

21. Step 2 – Enter numbers into cells
4 & 8

22. Step 3 – Call the function
= adder(A1,B1)

23. What happened? = adder(A1,B1) A B C 1 4 8 12 2 Function adder( a, b)
Function adder( a, b)
adder = a b
End Function

24. Rules for naming variables
Must begin with letter
Use only letters, numbers, and underscores
Do not use space, period (.), exclamation mark (!), or the &, $, #
Do not exceed 255 characters in length
Avoid names already used by Excel and VBA

25. Operator Precedence in Formulas
Parenthesis
Negation (–)
Exponentiation (^)
Multiplication and division (*, /)
Addition and subtraction (+, –)
answer = (5 + 7^2*3)/4 – 1
Evaluates as…
answer = (5 + 49*3)/4 – 1
answer = ( )/4 – 1
answer = (152)/4 – 1
answer = 38 – 1
answer = 37

26. Odd features of computer formulas…
In algebra, the following formula has no solution…
A = A +3
In computers, the above formula means …
Take the current value of A, add 3 to it, and make the result the new value of A.
In algebra, either of the following two formulas has meaning…
y = x or x + 3 = y
In computers, only the first formula is valid.

27. Integers and Real Numbers
Integer – Any positive or negative counting number, or zero.
Examples: 4, –7, 0
Real Number – Any rational or irrational number
Examples: 4.0, 0.75, , – 0.5
Note: Rational number – can be expressed as m/n where m and n are integers and n is not zero
Irrational number – cannot be expressed as m/n where m and n are integers and n is not zero

28. Integers and Real Numbers
Integer – Any positive or negative counting number, or zero.
Examples: 4, –7, 0
Real Number – Any rational or irrational number
Examples: 4.0, 0.75, , – 0.5
“Floating point” numbers are harder to represent in a computer
Note: Rational number – can be expressed as m/n where m and n are integers and n is not zero
Irrational number – cannot be expressed as m/n where m and n are integers and n is not zero

29. Declaring Variables
When introducing a new variable into a computer program, you should tell the computer what kind it is. Some common options…
Increasing memory requirements
Integer
Single – single-precision real number
Double – double-precision real number

30. Modify you program as follows…
Declared as integers
Function adder( a As Integer, b As Integer)
Dim c As Integer
c = 5
adder = a + b + c
End Function
What happens when you introduce real numbers into the Excel cells?

31. Comments
Comments can be added to help humans understand the program. Comments are ignored by the computer.
Function adder(a As Integer, b As Integer)
‘ This program adds two numbers together and adds 5
Dim c As Integer
c = 5
adder = a + b + c
End Function
The apostrophe signals the computer to ignore what follows
Indentation is also ignored my computer, but helps humans to understand.

32. What if a line is too long?
Example…
var = _
Is evaluated as
var =
The underscore joins lines together.

33. Types of Errors
Syntax errors – simple errors that do not follow the required format
Compiler errors – errors that occur when the computer program is converted to machine code
Run-time errors – a program may compile fine, but may fail during a run
Logic errors – a program may run fine, but have mistakes in logic that give incorrect answers
Spelling error – if you misspell a variable, the computer interprets it as an additional variable and likely will give incorrect answers

34. How to protect against spelling errors
This statement requires that all variables be declared
Option Explicit
Function adder(a As Integer, b As Integer)
'This program adds two numbers together and adds 5
Dim c As Integer
c = 5
adder = a + b + c
End Function
Do the following:
Add Option Explicit to your program
Misspell c = 5 as d = 5
Go to the Excel spreadsheet and try to use adder

35. Your function failed to run and you got an error message.
How to recover…
Press OK in the error message
Correct the spelling
Press F5
It is good programming practice to use
Option Explicit so that spelling errors are caught.

36. Comparison Operators 1. Equality (=) 2. Inequality (<>)
3. Less than (<)
4. Greater than (>)
5. Less than or equal to (<=)
6. Greater than or equal to (>=)
Evaluated in
this order of
precedence

37. Selection: If ? Function comparison(a, b) comparison = 0 Y
Calc A
Function comparison(a, b)
comparison = 0
If a > b Then
comparison = 1
End If
End Function
Enter the above program and test it in Excel.
(Note: Option Explicit can appear only once on a sheet, so it is omitted here.)

38. Selection: If-Else ? Function comparison(a, b) If a > b Then
End If
End Function Y ?
Calc A N
Calc B
Enter the above program and test it in Excel.
(Note: Option Explicit can appear only once on a sheet, so it is omitted here.)

39. Selection: If-ElseIf ? ? Y Function comparison(a, b) If a > b Then
ElseIf a = b Then
comparison = 2
Else
comparison = 3
End If
End Function
Calc A N Y ?
Calc B N
Calc C
Enter the above program and test it in Excel.
(Note: Option Explicit can appear only once on a sheet, so it is omitted here.)

40. Repetition: Do While Input Function do_while_loop(a As Integer) Title
Dim i As Integer
Dim j As Integer
i = 1
j = 1
Do While i < a
i = i + 1
j = j * 2
Loop
do_while_loop = j
End Function
Title
Declare variables
Initialize variables
Calculate
Output
Enter the above program and test it in Excel.

41. Repetition: Do While As a flowchart… i = 1 j = 1 N i < a? Y
Function do_while_loop(a As Integer)
Dim i As Integer
Dim j As Integer
i = 1
j = 1
Do While i < a
i = i + 1
j = j * 2
Loop
do_while_loop = j
End Function
i = 1
j = 1
i < a?
i = i +1
j = j *2 Y N

42. Repetition: For As a flowchart… i = 1 j = 1 Default: Y Counts by +1
Function for_loop(a As Integer)
Dim i As Integer
Dim j As Integer
j = 1
For i = 1 To a
j = j * 2
Next i
for_loop = j
End Function
i = 1
j = 1
i > a?
i = i +1
j = j *2 N
Default:
Counts by +1 Y
Enter the above program and test it in Excel.
Note: The code is shorter, but the flowchart is the same.

43. Repetition: For As a flowchart… i = a j = 1 Overrides default: Y
Function for_loop(a As Integer)
Dim i As Integer
Dim j As Integer
j = 1
For i = a To 1 Step -1
j = j * 2
Next i
for_loop = j
End Function
As a flowchart…
i = a
j = 1
Overrides default:
Counts by -1
i < 1? Y N
Enter the above program and test it in Excel.
i = i – 1
j = j *2

44. Bring
Math Supplement
to next class.