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Visual Basic Control Statements Essentials

Explore data types, arithmetic operators, algorithm design, and control structures in Visual Basic programming. Learn syntax rules, variable naming, and arithmetic operations. Understand comparison and control structures fundamentals.

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Visual Basic Control Statements Essentials

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  1. CSCI 3327 Visual Basic Chapter 4: Control Statements in Visual Basic (Part 1A) UTPA – Fall 2011

  2. 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

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

  4. 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

  5. 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)

  6. Primitive Data Types in Visual Basic • Boolean • Byte • Char • Date • Decimal • Double • Integer • Long • SByte • Short • Single • String • Uinteger • Ulong • UShort

  7. 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

  8. 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

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

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

  11. 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

  12. 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

  13. Sign Operations • Unary Minus • -e • E.g., -10, -3.14 • Unary Plus • +g • E.g., +100 (equivalent to 100)

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

  15. 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

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

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

  18. 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

  19. 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

  20. 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"

  21. Categories of Control Structures • Control Structures • Sequence structure • Selection structure • Repetition structure

  22. 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 Add grade to total Add 1 to counter

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

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

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

  26. 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 End If End If

  27. Alternative Version If grade >=90 Then write (“A”) ElseIf grade >=80 Then write(“B”) ElseIf grade >= 70 Then write(“C”) Else write(“D”) EndIf

  28. 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

  29. Example of Repetition • See example programs • DoWhile … Loop • Find the first power of 3 larger than 100 merge decision [product<=100] triple the product value [product>100]

  30. Example of Repetition (cont'd) • While + loop-continuation condition ------------------------------------------------------------------- DoWhile product <=100 product = product * 3 ' compute next power of 3 Loop ----------------------------------------------------------- While product <=100 product = product * 3 ' compute next power of 3 End While

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

  32. 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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