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UTPA – Fall 2011

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

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UTPA – Fall 2011

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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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