Visual Basic.NET Fundamentals

Objectives Use primitive data types, naming conventions, and style rules Understand and apply the control structures supported in Visual Basic.NET Explain the objects and techniques involved in the creation of a Multiple Document Interface (MDI) application Understand the purpose and uses of these new Windows Forms controls: TabControl, ComboBox, CheckBox, GroupBox, and RadioButton

Using Primitive Data Types, Naming Conventions, and Style Rules Data Types –Literal Has the face value of each occurrence –Constant Is assigned a literal value that does not change –Variable Is a symbolic reference to an address in memory Values stored memory block can change during program execution Naming Conventions –Facilitate program readability, understandability, and maintainability –Programmer-supplied names must be meaningful –Variable names are mixed case and consist of a prefix and a meaningful name

Using Primitive Data Types, Naming Conventions, and Style Rules (Continued) Example variable declarations –Dim mdecInterestRate As Decimal - A module-level decimal –Public pastructUser - A public array of structures –Static stintLineCtr - A static integer –Dim strMessage - A dynamic local string Naming constants –Const DAYSINWEEK = 7 Naming functions –Private Function GetNextRecord() –Public Sub FindLastName() –Protected Sub EnableDisableTextboxes(vbln As Boolean) Naming classes –Public Class Student –Public Class AcademicProgram Naming controls –Controls have a prefix indicating the control’s class

Coding Conventions and Style Rules Purpose: to increase code readability, and, therefore, make it easier to revise and debug Using indentation –To visually identify groups of related statements Declaring variables at the lowest level –If variable needed only inside a procedure, declare it inside that procedure –If variable needed only in one form, declare it at form level in that form –If a variable is needed only inside a standard module, declare it as a Private variable inside that module Using constants –Use constants rather than numeric values when possible –Constants improve program readability and also facilitate program maintenance Writing code that is easy to read –Try to write code that is easy to read, follow, and understand

Control Structures and Structured Programming Control structure –A method of controlling the execution sequence of instructions at runtime Characteristics of structured programs –Limited to sequence, selection, and iteration, with unlimited nesting –Every procedure has a single entry point and a single exit point –Using stepwise refinement, programs are broken down logically or functionally into relatively small blocks of code –Variables are declared at lowest possible level –Global variables are used minimally, if at all Stub –A placeholder for a section of code that will be developed later

Visual Basic.NET Control Structures Sequence structure –One statement after another Selection structure –Includes the If statement, Select Case statement, Immediate If function, and Try statement Iteration structures –Provide for the repeated execution of a statement block If statement –Allows you to specify a condition or test, and if that condition is met, to then execute one or more imperative statements

Logical Operators And –The result is True only when condition A and conditionB are both True Or –The result is True if at least one of conditionA or conditionB is True AndAlso –The result is True only when conditionA and conditionB are both True OrElse –The result is True if at least one of conditionA or conditionB is True Xor –The result is True only when one and only one of conditionA and conditionB is True

Truth Table for Visual Basic.NET Logical Operators

Visual Basic.NET Control Structures (Continued) Select case –Useful when the evaluation of a single expression can determine multiple paths Immediate If (IIf) –Examines and returns if the condition is True; otherwise, it returns –Syntax: = IIf(,, ) Try … Catch … Finally –Provides a structured programming solution to the problem of error trapping Do loops –Principal form of externally controlled loops –Pretest loop –Posttest loop –While test –Until test

For Loop Internally controlled loop Requires –Loop control variable (LCV) –Initial value for the LCV –Limit value for the LCV –Step value –Test to determine whether the LCV’s limit value has been reached (after which the loop is exited)

Using a For Loop for a Sequential Search