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CSI 1301 PROGRAMMING IN VISUAL BASIC PART 1

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Part 1 1. Visual Basic Programming 2. Translating the Algorithm Declaration 3. Translating Assignment Instructions 4. Translating Get and Give Instructions 5. Additional Material

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1. Visual Basic Programming

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Visual Basic Programming Visual Basic is a programming language for Windows applications We will use it to: –Run our algorithms on a computer Use the computer as the computing agent –Assist us in making more effective use of Excel To provide a suitable user interface in our worksheets To express complex logic in formulas (see the slides titled Example of Complexity in the Additional Material at the end of this lecture)

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Visual Basic Programming Creating an algorithm can be difficult –Think through the problem and solve it without using a computer However, with an algorithm, writing the program becomes easy –Translate the instructions in the algorithm to Visual Basic instructions English ALGORITHM Visual Basic

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Visual Basic Programming Problems encountered in developing an algorithm –Comprehension problems (“Misinterpretation”) –Process problems (“How do I solve it?) Problems encountered in a Visual Basic program –Syntax errors (Grammatical and spelling mistakes) –Semantic errors (Program runs but errors in logic lead to incorrect results) –Run time errors (Program fails when running ie. dividing by zero)

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2. Translating the Algorithm Description

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Translating the Algorithm Description When a program is executing, the instructions and data being processed are stored in RAM The following parts of the Algorithm Description tell us what data is to be stored and processed by our program –Givens –Intermediates –Results Each data item can be either a variable or a constant

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Translating the Algorithm Description Variable Is an address in RAM that has a name and contains a value The value can change as the code is executed Can hold only one value at a time Constant Has a value that does not change as the code is executed A meaningful name used in place of a value Names Begin with a letter Maximum of 255 characters in length Contain only letters, numbers and _ (underscore) Not case sensitive Cannot be a Visual Basic reserved word

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Translating the Algorithm Description We tell the Visual Basic translator what type of data is to be processed by our program by defining data types Each data type determines –The kind of data which can be stored in RAM –The range of possible values –How many bytes of RAM will be used to store it –The type of operations that can be performed on the data The Visual Basic translator can then Determine how and where to store that data in RAM Tell us if we try to do something silly in our program –15 + “joe smith” = ??? –Store text in a numeric variable

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Translating the Algorithm Description The Visual Basic translator keeps track of where each data item is stored in RAM When we want to reference the value of a data item, we simply use its name. The Visual Basic translator knows where to go in RAM to find the value.

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Translating the Algorithm Description Declaring variables and constants in a program –Done with a DIM statement for a variable Also specify the data type with the As clause Advantages –Code is easier to read –Speeds up execution of code –Conserves memory space –Done with a CONST statement for a constant Option Explicit must be used in the first line –Forces all variables and constants to be declared –(also useful to detect misspelled variable and constant names)

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Translating the Algorithm Description Enter OPTION EXPLICIT on the first line All programs begin with SUB and end with END SUB Comments are lines that are ignored by the computer. –We use them to make our code easier to read –Everything to the right of a ‘ (single quote) is a comment Look at GIVENS, INTERMEDIATES and RESULTS –Each entry must be declared –Also define the type for each variable

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Translating the Algorithm Description OPTION EXPLICIT 'WRITTEN BY T. JAMES SUB myprogram () DIM studnum as String*7 'Student Number DIM MT as Single 'Midterm Exam DIM FE as Single 'Final Exam DIM NG as Single 'Numeric Grade CONST PI = 3.14159 'PI END SUB

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Translating the Algorithm Description Where do we enter this code? –In the Visual Basic Editor in Excel To open the Editor –select Tools – Macro – Visual Basic Editor –or right click a worksheet tab and select View Code (not recommended) –or press Alt + F11 Then select Insert – Module Then enter the code The Visual Basic Editor is described in more detail in the Additional Material at the end of these lecture slides

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3. Translating Assignment Instructions

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Algorithmic Representation of Computer Functions Input –Get information Storage –Store information Process –Arithmetic operations –Logic decisions –Repeat instructions Output –Give information GET Given/Results/Intermediates/Set LET IF LOOP GIVE

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Assignment Instructions An assignment statement is used to assign a value to a variable Variable = Expression –The computed value of the Expression is assigned to (stored in) the variable on the left side of the = sign

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Assignment Instructions X = 5 –Take the value of 5 and store it in X Y = X + 3 –Take the value of X (5) and add 3 to get 8 –Store 8 in Y X = X + 1 –NOT AN ALGEBRAIC EQUATION –Take the value of X (5) and add 1 to get 6 –Store 6 in X (replacing the value of 5)

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Assignment Instructions The order of precedence of arithmetic operators in an expression is as follows: Brackets () Exponents ^ Division / Multiplication * Addition + Subtraction -

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Translating Assignment Instructions Look at the METHOD. Translate any instruction with an = sign as an assignment statement Each assignment statement is one line of code –Write each in the proper form Variable = Expression

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Translating Assignment Instructions ALGORITHM X = 5 Y = X + 3 C = 2 r A = r 2 VISUAL BASIC X = 5 Y = X + 3 C = 2 * PI * R A = PI * R^2

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Translating Assignment Instructions Option Explicit 'Written by T. James Sub Circles() Dim R as Single 'Radius Dim A as Single 'Area Dim C as Single 'Circumference Const PI = 3.1415926 R = 1.2 A = PI * R^2 C = 2 * PI * R End Sub

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4.Translating Get and Give Instructions From/To the User

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GET/GIVE from/to the User At the most basic level, our programs –get information from the user (input) via the keyboard or mouse, and –give information to the user (output) via the screen Therefore, we need Visual Basic instructions to –read user input from the keyboard or mouse, and –write information on the screen

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GET from the User An InputBox is used to get information that is entered by the user at the keyboard Variable = InputBox(“prompt message”, “title”, “default input”, Xcor, Ycor) –Variable stores the information entered by the user –Prompt message describes what we want the user to enter –Title appears in the title bar at the top of the InputBox –Default input shows a sample of the type of information to be entered –Xcor and Ycor are the X and Y axes coordinates that position the InputBox on the screen

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GET from the User Frequently, we do not need to specify the title, default input or positioning coordinates –Then the Visual Basic instruction to get information from the user can be simplified to Variable = InputBox(“prompt message”) Name = InputBox(“Enter your Name”) –When this statement is executed, an InputBox will appear on the user’s screen –The InputBox will contain the text, Enter your Name –It will also contain a rectangle –The information entered by the user will appear in this rectangle –The InputBox will also contain an OK button –When the user has entered his/her name, he/she will click the OK button and the information entered will be stored in the variable Name

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GET from the User Income = InputBox(“Enter your income”) –Stores what the user enters in the variable Income

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GIVE to the User A MsgBox is used to send information to the screen for the user to view –We will explore the full capabilities of the MsgBox later For now, we can use the following statement MsgBox(“message”) –Message is the information that will be displayed in the MsgBox on the screen –The MsgBox will also contain an OK button –When the user has read the message, he/she will click the OK button and the MsgBox will disappear from the screen

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GIVE to the User MsgBox(“The Tax is “ & Tax) –Takes the string “The Tax is “ and concatenates it with the value of the variable Tax –Displays the result on the screen in a MsgBox Concatenation can also be accomplished with + Preferable to use &

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Look at the METHOD Translate any GET or GIVE instructions that refer to the user as follows. –GIVE: MsgBox(“message”) –GET: variable = InputBox(“prompt message”) Translating to Visual Basic

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Translate 1 Translate Algorithm 1.5 –NAME: CalcMark –GIVENS: A1, A2, A3 –RESULTS: Mark –INTERMEDIATES: Total, MaxMark (Constant) –DEFINITION: Mark := CalcMark(A1, A2, A3) –METHOD: Set MaxMark = 140 Get A1 Get A2 Get A3 Let Total = A1 + A2 + A3 Let Mark = Total/MaxMark * 100 Give Mark Option Explicit 'Written By T. James

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Translate 1 Translate Algorithm 1.5 –NAME: CalcMark –GIVENS: A1, A2, A3 –RESULTS: Mark –INTERMEDIATES: Total MaxMark(Constant) –DEFINITION: Mark := CalcMark(A1, A2, A3) –METHOD: Set MaxMark = 140 Get A1 Get A2 Get A3 Let Total = A1 + A2 + A3 Let Mark = Total/MaxMark * 100 Give Mark Option Explicit 'Written By T. James Sub CalcMark ()

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Translate 1 Translate Algorithm 1.5 –NAME: CalcMark –GIVENS: A1, A2, A3 –RESULTS: Mark –INTERMEDIATES: Total MaxMark (Constnat) –DEFINITION: Mark := CalcMark(A1, A2, A3) –METHOD: Set MaxMark = 140 Get A1 Get A2 Get A3 Let Total = A1 + A2 + A3 Let Mark = Total/MaxMark * 100 Give Mark Option Explicit 'Written By T. James Sub CalcMark () Dim A1 as Integer Dim A2 as Integer Dim A3 as Integer Dim Mark as Single Dim Total as Integer Const MaxMark =140

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Translate 1 Translate Algorithm 1.5 –NAME: CalcMark –GIVENS: A1, A2, A3 –RESULTS: Mark –INTERMEDIATES: Total MaxMark (Constant) –DEFINITION: Mark := CalcMark(A1, A2, A3) –METHOD: Set MaxMark = 140 Get A1 Get A2 Get A3 Let Total = A1 + A2 + A3 Let Mark = Total/150 * 100 Give Mark Option Explicit ‘Written By T. James Sub CalcMark () Dim A1 as Integer Dim A2 as Integer Dim A3 as Integer Dim Mark as Single Dim Total as Integer Const MaxMark = 140 A1 = InputBox("A1?") A2 = InputBox("A2?") A3 = InputBox("A3?")

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Translate 1 Translate Algorithm 1.5 –NAME: CalcMark –GIVENS: A1, A2, A3 –RESULTS: Mark –INTERMEDIATES: Total, MaxMark (Constant) –DEFINITION: Mark := CalcMark(A1, A2, A3) –METHOD: Set MaxMark = 140 Get A1 Get A2 Get A3 Let Total = A1 + A2 + A3 Let Mark = Total/MaxMark * 100 Give Mark Option Explicit 'Written By T. James Sub CalcMark () Dim A1 as Integer Dim A2 as Integer Dim A3 as Integer Dim Mark as Single Dim Total as Integer Const MaxMark = 140 A1 = InputBox("A1?") A2 = InputBox("A2?") A3 = InputBox("A3?") Total = A1 + A2 + A3 Mark = Total/150 * 100

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Translate 1 Translate Algorithm 1.5 –NAME: CalcMark –GIVENS: A1, A2, A3 –RESULTS: Mark –INTERMEDIATES: Total, MaxMark (Constant) –DEFINITION: Mark := CalcMark(A1, A2, A3) –METHOD: Set MaxMark = 140 Get A1 Get A2 Get A3 Let Total = A1 + A2 + A3 Let Mark = Total/150 * 100 Give Mark Option Explicit 'Written By T. James Sub CalcMark () Dim A1 as Integer Dim A2 as Integer Dim A3 as Integer Dim Mark as Single Dim Total as Integer Const MaxMark = 140 A1 = InputBox("A1?") A2 = InputBox("A2?") A3 = InputBox("A3?") Total = A1 + A2 + A3 Mark = Total/150 * 100 MsgBox("Mark is " & Mark) End Sub

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5. Additional Material Example of Complexity Visual Basic Editor Translation Set 1

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Example of Complexity Student Marks

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Example of Complexity Calculate the final mark, based on 25% for assignments, 25% for midterm and 50% for final examination –insert the following formula in cell j2 & copy it to the other cells in column j =0.5*(SUM(c2:g2))+0.25*h2+0.5*i2 Variation 1 –“If the student failed the final exam, then he/she fails the course.” =IF(i2>=50,formula as above,i2)

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Example of Complexity Variation 2 –“If the student failed the final exam, then the weighted sum of 1/3 midterm mark and 2/3 final exam mark must be 50 or more for the student to pass the course.” =IF(i2 =50,as above,i2),as above) Variation 3 –Assign letter grades to the final marks –a more complex case »(more nesting required) –the need to write code »(a user defined function)

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Visual Basic Editor The Visual Basic Editor –Consists of 4 windows Main, Code, Project Explorer, Properties 1 Main window –Title bar, menu bar & standard toolbar 2 Code window –Insert – Module –To write code for procedures

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Visual Basic Editor 3 Project Explorer window Shows the open project (name of file containing the project) Shows the worksheets & modules in the project (in a format similar to Windows Explorer) Has 3 buttons –View Code: view the code in the module selected –View Object: view the worksheet selected –Toggle Folders: control the display of the folder 4 Properties window –To change properties for any worksheet or module –Properties control an object’s appearance & behaviour

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Translation Set 1

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Translate 2 Translate Algorithm 1.4 NAME:AVG3 GIVENS: Num1, Num2, Num3 RESULTS: Sum, Average DEFINITION: Sum & Average := AVG3(Num1, Num2, Num3) METHOD: Get Num1 Get Num2 Get Num3 Let Sum = Num1 + Num2 + Num3 Let Average = Sum /3 Give Sum Give Average Option Explicit 'Written By T. James Sub AVG3 () Dim Num1 as Integer Dim Num2 as Integer Dim Num3 as Integer Dim Sum as Integer Dim Average as Single Num1 = InputBox("Num1?") Num2 = InputBox("Num2?") Num3 = InputBox("Num3?") Sum = Num1 + Num2 + Num3 Average = Sum/3 MsgBox("SUM = " & Sum) MsgBox("Average = " & Average) End Sub

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Translate 3 NB Div is Implemented as \ Translate Algorithm 1.6 NAME: SumDig GIVENS: N RESULTS: Sum INTERMEDIATES: Tens, Ones DEFINITION: Sum := SumDig(N) METHOD: Get N Let Tens = N div 10 Let Ones = N mod 10 Let Sum = Tens + Ones Give Sum Option Explicit 'Written By T. James Sub SumDig () Dim N as Integer Dim Sum as Integer Dim Tens as Integer Dim Ones as Integer N = InputBox("2 Dig Num?") Tens = N \ 10 Ones = N mod 10 Sum = Tens + Ones MsgBox("Total is " & Sum) End Sub

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Homework

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What value is assigned to z by the statement below, assuming z, a, b, w and y have respectively the values 8, 3, 9, 2 et –5. z = z - (a + b / 2) + w * -y

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1. Write an algorithm to sum 5 numbers. Translate the algorithm into Visual Basic code 2. Write an algorithm to compute the average of 5 numbers. Translate the algorithm into Visual Basic code 3. Write an algorithm to multiply 3 numbers. Translate the algorithm into Visual Basic code 4. Write an algorithm to multiply 2 numbers and divide the product by a third number. Translate the algorithm into Visual Basic code

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1. Write an algorithm to calculate the average mark out of 100, given three assignment marks, each of which is marked out of 20. Translate the algorithm into Visual Basic code 2. Write an algorithm to calculate the sum of the digits of a three digit number. Translate the algorithm into Visual Basic code 3. Write an algorithm to swap two numbers. Translate the algorithm into Visual Basic code 4. Write an algorithm to sum four numbers and return the sum in the variable x. Translate the algorithm into Visual Basic code

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