1. Microsoft Visual Basic 2005 BASICSyo
Microsoft Visual Basic 2005 BASICS
Lesson 8
If Statements

2. Objectives Explain how decisions are made in a computer.yo
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.
Microsoft Visual Basic 2005 BASICS

3. Objectives (cont.) Use If…Else statements. Use check box controls.yo
Objectives (cont.)
Use If…Else statements.
Use check box controls.
Use the logical operators.
Microsoft Visual Basic 2005 BASICS

4. The Building Blocks of Decision Makingyo
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
Microsoft Visual Basic 2005 BASICS

5. The Building Blocks of Decision Making (cont.)
Microsoft Visual Basic 2005 BASICS

6. Using the Conditional Operatorsyo
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
Microsoft Visual Basic 2005 BASICS

7. Using the Conditional Operators (cont.)
Microsoft Visual Basic 2005 BASICS

8. Using the Conditional Operators (cont.)
Microsoft Visual Basic 2005 BASICS

9. Using If Statements If statementyo
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.
Microsoft Visual Basic 2005 BASICS

10. 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.
Microsoft Visual Basic 2005 BASICS

11. Creating and Reading Flowchartsyo
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.
Microsoft Visual Basic 2005 BASICS

12. Creating and Reading Flowcharts (cont.)
Microsoft Visual Basic 2005 BASICS

13. Creating and Reading Flowcharts (cont.)
Microsoft Visual Basic 2005 BASICS

14. Using If…Else Statementsyo
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
Microsoft Visual Basic 2005 BASICS

15. 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.
Microsoft Visual Basic 2005 BASICS

16. Using If…Else Statements (cont.)
Microsoft Visual Basic 2005 BASICS

17. Using If…Else Statements (cont.)
Microsoft Visual Basic 2005 BASICS

18. yo
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
Microsoft Visual Basic 2005 BASICS

19. Using Check Boxes (cont.)
Microsoft Visual Basic 2005 BASICS

20. Checked Property Each check box has a Checked property.yo
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
Microsoft Visual Basic 2005 BASICS

21. Checked Property (cont.)
Microsoft Visual Basic 2005 BASICS

22. Setting the Default Checked Property
Check boxes can be set to be either checked or unchecked by default.
Use the Checked property
Microsoft Visual Basic 2005 BASICS

23. Setting the Checked Property with Codeyo
Setting the Checked Property with Code
The Checked property can be set and/or read from code.
Example
chkHeart.Checked = True
Microsoft Visual Basic 2005 BASICS

24. Setting the Checked Property with Code (cont.)
Microsoft Visual Basic 2005 BASICS

25. Using the Logical Operatorsyo
Using the Logical Operators
Logical operators
Can be used to combine several comparisons into one statement
Used with True and False values
Microsoft Visual Basic 2005 BASICS

26. Using the Logical Operators (cont.)
Microsoft Visual Basic 2005 BASICS

27. Order of Logical Operatorsyo
Order of Logical Operators
Logical operators
Processed after the mathematical and conditional operators
Logical operators are processed in this order
Not
And Or
Microsoft Visual Basic 2005 BASICS

28. Order of Logical Operators (cont.)
Microsoft Visual Basic 2005 BASICS

29. yo
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.
Microsoft Visual Basic 2005 BASICS

30. 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.
Microsoft Visual Basic 2005 BASICS

31. 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.
Microsoft Visual Basic 2005 BASICS

32. 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.
Microsoft Visual Basic 2005 BASICS

33. 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.
Microsoft Visual Basic 2005 BASICS

34. 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.
Microsoft Visual Basic 2005 BASICS