CSCI 3327 Visual Basic Chapter 4: Control Statements in 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 2

Introduction Computer program –Sequence of statements whose objective is to accomplish a task Programming –Process of planning and creating a program 3

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 4

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) 5

Primitive Data Types in Visual Basic Boolean Byte Char Date Decimal Double Integer Long 6 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 7

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 8

Arithmetic Operators in Visual Basic Addition: + Subtraction: - Multiplication: * Division (floating point): / Division (integer): \ Modulus: Mod Exponentiation: ^ 9

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

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 11

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

Sign Operations Unary Minus –-e –E.g., -10, Unary Plus –+g –E.g., +100 (equivalent to 100) 13

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 14 priority high 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 ^ *

Comparison Operators Equality operators –= (equal) –<> (not equal) Relational operators –> –< –>= –<= 16

Rules of Operator Precedence ^ +, - (sign operations) *, / \ Mod +, - (addition and subtraction) =, <>,, >= (equality and relational) 17 priority high low

Example 3.27: Comparison.vb URL: _htp_2010/codeexamples.html _htp_2010/codeexamples.html TextBox –Set MultiLine property to true –AppendText method –vbCrLf – press an "enter" key 18

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 19

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" 20

Categories of Control Structures Control Structures –Sequence structure –Selection structure –Repetition structure 21

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 22 Add grade to total Add 1 to counter

Selection Structure If … Then If … Then … Else Select … Case 23 display "passed" [grade>=60] [grade<60]

Selection (1) If … Then –If grade >= 60 Then write(“Passed”) End If 24

Selection (2) If … Then … Else –If grade >= 60 Then write(“Passed”) Else write (“Failed”) End If 25

Nested Selection If grade >= 90 Then write(“A”) Else If grade >= 80 Then write(“B”) Else If grade >= 70 Then write(“C”) Else write(“F”) End If 26

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 27

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 28

Example of Repetition See example programs –Do While … Loop –Find the first power of 3 larger than 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 3 Loop While product <=100 product = product * 3 ' compute next power of 3 End While 30

Example of Repetition (cont'd) Until + loop-termination condition Do Until product > 100 product = product * 3 ' compute next power of 3 Loop 31

Example 4.12: ClassAverage.vb URL: _htp_2010/codeexamples.html _htp_2010/codeexamples.html ListBox –gradeListBox.Items.Add(gradeTextBox.Text) –gradeListBox.Items(gradeCounter) –gradeListBox.Items.Count 32

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