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**Programming in Visual Basic**

Class 2 Programming in Visual Basic

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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

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**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

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

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**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

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**What are some programming languages?**

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

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**What is Visual Basic for Applications (VBA)?**

It is a version of Visual Basic that is embedded within Excel.

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**Why are we learning VBA, rather than another programming language?**

Simple Easy to learn Quickly learned Capitalizes on your knowledge of Excel

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**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

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**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

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Creating a VBA program

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Step 1 – Open Excel

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Step 2 – Save as… Save as … Example_1

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Step 3 – Open VBA Editor Press… Alt F11

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**Step 4 – Identify where to file your program**

Left-click here

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Step 5 – Insert module Left click Insert Left click Module

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**A blank form will appear**

This is where the program goes

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Step 6 – Type in program Here is the program

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Use your program

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**Step 1 – Go to Excel spreadsheet**

Left click Excel button

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**Step 2 – Enter numbers into cells**

4 & 8

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**Step 3 – Call the function**

= adder(A1,B1)

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**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

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**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

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**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

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**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.

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**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

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**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

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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

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**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?

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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.

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**What if a line is too long?**

Example… var = _ Is evaluated as var = The underscore joins lines together.

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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

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**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

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**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.

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**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

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**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.)

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**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.)

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**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.)

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**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.

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**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

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**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.

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**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

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Bring Math Supplement to next class.

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