Programming in Visual Basic Class 2 Programming in Visual Basic

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

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

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

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

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

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

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

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

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

Creating a VBA program

Step 1 – Open Excel

Step 2 – Save as… Save as … Example_1

Step 3 – Open VBA Editor Press… Alt F11

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

Step 5 – Insert module Left click Insert Left click Module

A blank form will appear This is where the program goes

Step 6 – Type in program Here is the program

Use your program

Step 1 – Go to Excel spreadsheet Left click Excel button

Step 2 – Enter numbers into cells 4 & 8

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

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

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

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 = (5 + 147)/4 – 1 answer = (152)/4 – 1 answer = 38 – 1 answer = 37

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 +3 or x + 3 = y In computers, only the first formula is valid.

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, 3.14159, – 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

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, 3.14159, – 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

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

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?

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.

What if a line is too long? Example… var = 1 + 2 + 3 + 4 + _ 5 + 6 + 7 + 8 Is evaluated as var = 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 The underscore joins lines together.

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

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

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.

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

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.)

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.)

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.)

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.

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

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.

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

Bring Math Supplement to next class.