Mastering Selection Structures in Visual Basic Programming
Learn to implement selection structures in Visual Basic with If...Then...Else statements, comparison operators, and interface design with check boxes. Understand flowcharts, algorithms, variable scopes, and problem-solving approaches in programming.
Mastering Selection Structures in Visual Basic Programming
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Presentation Transcript
Clearly Visual Basic: Programming with Visual Basic 2008 Chapter 9 Decisions, Decisions, Decisions
Objectives • Show the selection structure in both pseudocode and a flowchart • Write If…Then…Else statements • Include comparison operators in a selection structure’s condition • Add a check box to an interface Clearly Visual Basic: Programming with Visual Basic 2008
Someone Might Need to Make a Decision • All computer programs are written using one or more of three control structures • Sequence, selection, or repetition • Selection structure • Makes a decision and then takes appropriate action based on that decision • Studying problem specification • Determines whether problem’s solution requires a selection structure Clearly Visual Basic: Programming with Visual Basic 2008
Going Beyond Rob’s Problems Figure 9-5 shows: Problem specification that does not involve Rob, the mechanical man Correct algorithm for the problem Clearly Visual Basic: Programming with Visual Basic 2008
The If … Then … Else Statement • Comparison operators • Used to compare values • Statement block • Set of statements contained in the true path and the false path • All expressions containing a comparison operator • Will result in an answer of either True or False only Clearly Visual Basic: Programming with Visual Basic 2008
Examining Another Problem Specification • Oval in a flowchart • Is the start/stop symbol • Rectangle in a flowchart • Is the process symbol • Parallelogram in a flowchart • Is the input/output symbol • Diamond in a flowchart • Is called the selection/repetition symbol Clearly Visual Basic: Programming with Visual Basic 2008
Hey, That’s Not the Way I Would Have Done It • Variable that has procedure scope • Can be used anywhere within the procedure • Variable that has block scope • Can be used only within the statement block in which it is declared • Block variable • Variable declared within a statement block Clearly Visual Basic: Programming with Visual Basic 2008
Summary • Selection structure • One of the three control structures • Indent instructions in a selection structure’s true path and its false path • In Visual Basic • You can use the If…Then…Else statement to code the selection structure • An expression containing a comparison operator • Will always evaluate to either True or False Clearly Visual Basic: Programming with Visual Basic 2008
Summary (continued) • In a flowchart • The selection structure’s condition is represented by a diamond • chk • The three-character ID used when naming check boxes • Block variable • Has block scope Clearly Visual Basic: Programming with Visual Basic 2008
