ppt lesson 08

Microsoft Visual Basic 2005 BASICS

Lesson 8

If Statements

Microsoft Visual Basic 2005 BASICS 2

Objectives

Explain how decisions are made in a computer.

Use the conditional operators. Use If statements to make decisions in

programs. Create and read basic flowcharts.


Objectives (cont.)

Use If…Else statements. Use check box controls. Use the logical operators.


The Building Blocks of Decision Making

Programs are limited without the ability to make decisions.

Programs must have a means to make decisions.

Decision making in computers Generally done in terms of a comparison

that returns a True or False response


The Building Blocks of Decision Making (cont.)


Using the Conditional Operators

The first step to making a decision in a program is to make a comparison.

Comparisons are made using the conditional operators.

Boolean variables Can be used to store the results of a

conditional expression


Using the Conditional Operators (cont.)


Using If Statements

If statement Allows you to execute specified code when

the result of a conditional expression is True

The End If statement marks the end of the If statement.


Using If Statements (cont.)

Code in between the If statement and End If statement is executed if the conditions specified in the If statement are true. Otherwise, the code is skipped.


Creating and Reading Flowcharts

Flowcharts Help you to plan and document program

code There are many symbols used in creating

flowcharts. The rectangle represents processing data. Use the diamond for making decisions. Use the parallelogram to represent input and

output.


Creating and Reading Flowcharts (cont.)


Using If…Else Statements

A one-way selection structure Program structure in which the decision is

to go “one way” The If…Else statement

Allows you to choose between two paths


Using If…Else Statements (cont.)

In an If…Else statement One block of code is executed if the result

of an expression is True. Another block is executed if the result is

False.


Using Check Boxes

Check boxes are an important part of the Windows interface.

Check boxes allow the programmer to Ask the user a Yes or No question Turn an option on or off


Using Check Boxes (cont.)


Checked Property

Each check box has a Checked property. Set to True if the box is checked Set to False if the box is not checked

A check box has an integrated label. Appears beside it Text property specifies its label


Checked Property (cont.)


Setting the Default Checked Property

Check boxes can be set to be either checked or unchecked by default. Use the

Checked property


Setting the Checked Property with Code

The Checked property can be set and/or read from code.

Example chkHeart.Checked = True


Setting the Checked Property with Code (cont.)


Using the Logical Operators

Logical operators Can be used to combine several

comparisons into one statement Used with True and False values


Using the Logical Operators (cont.)


Order of Logical Operators

Logical operators Processed after the mathematical and

conditional operators Logical operators are processed in this

order Not And Or


Order of Logical Operators (cont.)


Summary

Decisions are reached by making comparisons. Comparisons in a computer generally return either a True or False value.

The conditional operators compare two values and return either True of False, depending on whether the expression is True or False.


Summary (cont.)

A Boolean variable can be used to store the results of an expression that includes conditional operators.

The If statement is the most common way to make a decision in a program, and it is a one-way selection structure. The code between the If and the End If is executed if the conditions in the If statement are met.


Summary (cont.)

Flowcharts allow programmers to plan and document program code using symbols connected by lines.

An If…Else statement makes a decision between two paths, and it is a two-way selection structure.


Summary (cont.)

Check boxes allow your program to ask the user Yes or No questions or to turn an option on or off. The Checked property of a check box is set to True when the check box is checked and False when the check box is not checked. A check box can be set to be checked or unchecked by default.


Summary (cont.)

Logical operators can be used to combine several comparisons into one statement. They are used with True and False values.

The Not operator reverses the value of a Boolean variable or expression.

The And operator returns True if the values connected by the And operator are both True.


Summary (cont.)

The Or operator returns True if either value connected by the Or operator is True.

The logical operators are last in the order of operations. Of the logical operators, Not comes first, then And, then Or.

ppt lesson 08

Technology