CSCI 3327 Visual Basic Chapter 4 Control Statements

CSCI 3327 Visual Basic Chapter 4: Control Statements in Visual Basic (Part 1 A) 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; accomplishes something when executed, • 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 • • SByte Short Single String Uinteger Ulong UShort 6

Declaration of Variables • All variables must be declared before they are used in a program • Declaring a variable – Dim number 1 As Integer – Dim number 2 As Integer • Declaring multiple variables of the same type – Dim number 1, number 2 As Integer 7

Naming Convention • Camel case – Variable / function name – E. g. , tax. Rate, salary. Payment • Control naming convention – Variable name = the meaning of control's value+ control's type – E. g. , number 1 Label, number 2 Text. Box • 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 1. 775 10

Division (cont'd) • Division (integer) –xy – x and y are integers • 74 evaluates to 1, and 175 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. 14 evaluates to 1, and 7. 74 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 1024 12

Sign Operations • Unary Minus – -e – E. g. , -10, -3. 14 • Unary Plus – +g – E. g. , +100 (equivalent to 100) 13

Rules of Operator Precedence • • priority high ^ +, - (sign operations) *, / Mod +, - (addition and subtraction) low If there are several operators of the same priority, then they are evaluated from left to right 14

Exercises • What are the values of the following expressions? – 5. 2/2 – 9 Mod 3 – 42 – 4. 42 • What is the order of the following expression? –X=2*5^2+3*5+7 15

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

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

Example 3. 27: Comparison. vb • URL: http: //media. pearsoncmg. com/ph/esm/deitel/vb _htp_2010/codeexamples. html • Text. Box – Set Multi. Line property to true – Append. Text method – vb. Cr. Lf – 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 Go. To statement – Go. To 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 "Go. To 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 Add grade to total • UML activity diagram – Flowchart – Initial state action state 1 … action state n final state Add 1 to counter 22

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

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”) Else. If grade >=80 Then write(“B”) Else. If 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 100 merge decision [product>100] [product<=100] triple the product value 29

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: Class. Average. vb • URL: http: //media. pearsoncmg. com/ph/esm/deitel/vb _htp_2010/codeexamples. html • List. Box – grade. List. Box. Items. Add(grade. Text. Box. Text) – grade. List. Box. Items(grade. Counter) – grade. List. Box. Items. Count 32

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