CSCI 3327 Visual Basic CSCI 3327 Visual Basic Chapter 4: Control Statements in Chapter 4: Control Statements in

Visual Basic (Part 1A)Visual Basic (Part 1A)

UTPA – Fall 2011

Objectives

• In this chapter, you will:– Learn the primitive data types in Visual Basic– Become familiar with arithmetic operators– Explore how to design algorithms to solve

problems– Learn the components of basic control structures– Study the syntax of basic sequence, selection, and

repetition structures in Visual Basic

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Introduction

• Computer program– Sequence of statements whose objective is to

accomplish a task

• Programming – Process of planning and creating a program

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Introduction (cont'd)

• Function– Collection of statements; when executed,

accomplishes something

• Syntax– Rules that specify which statements (instructions)

are legal

• Programming language– A set of rules, symbols, and special words– Visual Basic

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Introduction (cont'd)

• Reserved words, keywords, or word symbols– Words that are reserved by Visual Basic– Usually in blue color in the IDE (Visual Studio)

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Primitive Data Types in Visual Basic

• Boolean• Byte• Char• Date• Decimal• Double• Integer• Long

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• SByte

• Short

• Single

• String

• Uinteger

• Ulong

• UShort

Declaration of Variables

• All variables must be declared before they are used in a program

• Declaring a variable– Dim number1 As Integer– Dim number2 As Integer

• Declaring multiple variables of the same type– Dim number1, number2 As Integer

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Naming Convention

• Camel case – Variable / function name– E.g., taxRate, salaryPayment

• Control naming convention– Variable name = the meaning of control's value+

control's type– E.g., number1Label, number2TextBox

• Although the variable/function name is not case sensitive, it is important to follow a consistent naming convention

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Arithmetic Operators in Visual Basic

• Addition: +

• Subtraction: -

• Multiplication: *

• Division (floating point): /

• Division (integer): \

• Modulus: Mod

• Exponentiation: ^

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Division

• Division (floating point)– x / y– E.g., 7.l / 4 evaluates to 1.775

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Division (cont'd)

• Division (integer)– x \ y– x and y are integers

• 7\4 evaluates to 1, and 17\5 evaluates to 3

– x and y are not integers• Numbers are first rounded to the nearest whole number

• E.g., 7.1 is rounded to 7, and 7.7 is rounded to 8

• Thus, 7.1\4 evaluates to 1, and 7.7\4 yields 2

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Modulus & Exponentiation

• Modulus– r Mod s– 7 Mod 3 evaluates to 1 (since 7=3*2+1)

• Exponentiation– 3^2 evaluates to 3*3=9– 2^3 evaluates to 2*2*2=8– 2^10 evaluates to 1024

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Sign Operations

• Unary Minus– -e– E.g., -10, -3.14

• Unary Plus– +g– E.g., +100 (equivalent to 100)

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Rules of Operator Precedence

• ^

• +, - (sign operations)

• *, /

• \

• Mod

• +, - (addition and subtraction)

• If there are several operators of the same priority, then they are evaluated from left to right

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priorityhigh

low

Exercises

• What are the values of the following expressions?– 5.2/2– 9 Mod 3– 4\2– 4.4\2

• What is the order of the following expression?– X = 2 * 5 ^ 2 + 3 * 5 + 7

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Comparison Operators

• Equality operators– = (equal)– <> (not equal)

• Relational operators– >– <– >=– <=

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Rules of Operator Precedence

• ^• +, - (sign operations)• *, /• \• Mod• +, - (addition and subtraction)• =, <>, <, <=, >, >= (equality and relational)

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priority

high

low

Example 3.27: Comparison.vb

• URL: http://media.pearsoncmg.com/ph/esm/deitel/vb_htp_2010/codeexamples.html

• TextBox– Set MultiLine property to true– AppendText method– vbCrLf – press an "enter" key

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Problem Solving Techniques

• Problem-solving process has three steps:– Analyze problem and design an algorithm– Implement the algorithm in code– Maintain the program

• Algorithm is independent of languages – Actions to be executed, and – The order in which these actions are executed

• Pseudo code

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Control Structures

• Problem with the GoTo statement– GoTo statement can specify a control to any place

(line or destination) in a program– Making the program unstructured and hard to

follow

• Research indicates that all programs can be written by only 3 control structures– With "GoTo elimination"

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Categories of Control Structures

• Control Structures– Sequence structure– Selection structure– Repetition structure

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Sequence Structure

• Visual Basic statement– total = total + grade– counter=counter+1

• UML activity diagram– Flowchart – Initial state action state 1

… action state n

final state

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Add grade to total

Add 1 to counter

Selection Structure

• If … Then

• If … Then … Else

• Select … Case

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display "passed"

[grade>=60]

[grade<60]

Selection (1)

• If … Then– If grade >= 60 Then

write(“Passed”)

End If

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Selection (2)

• If … Then … Else– If grade >= 60 Then

write(“Passed”)

Else

write (“Failed”)

End If

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Nested SelectionIf grade >= 90 Then write(“A”)Else If grade >= 80 Then write(“B”) Else If grade >= 70 Then write(“C”) Else write(“F”) End If End IfEnd If

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Alternative Version

If grade >=90 Then write (“A”)ElseIf grade >=80 Then write(“B”)ElseIf grade >= 70 Then write(“C”)Else write(“D”)End If

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Repetition Structure

• Visual Basic provides 7 repetition statements– Do While … Loop– While … End While– Do Until … Loop– Do … Loop While– Do … Loop Until– For … Next– For Each … Next

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Example of Repetition

• See example programs– Do While … Loop– Find the first power of 3 larger than 100

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triple the product value

[product<=100]

[product>100]

decision

merge

Example of Repetition (cont'd)

• While + loop-continuation condition-------------------------------------------------------------------Do While product <=100 product = product * 3 ' compute next power of 3Loop

-----------------------------------------------------------While product <=100 product = product * 3 ' compute next power of 3End While

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Example of Repetition (cont'd)

• Until + loop-termination condition-------------------------------------------------------------------

Do Until product > 100

product = product * 3 ' compute next power of 3

Loop

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Example 4.12: ClassAverage.vb

• URL: http://media.pearsoncmg.com/ph/esm/deitel/vb_htp_2010/codeexamples.html

• ListBox– gradeListBox.Items.Add(gradeTextBox.Text)– gradeListBox.Items(gradeCounter)– gradeListBox.Items.Count

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