Conditionals and Boolean Expressions - PowerPoint PPT Presentation

1 / 29

About This Presentation

Title:

Conditionals and Boolean Expressions

Description:

If the if clause didn't execute, the else clause will! Has format: if ( boolean value ... Accept anyone not named Bob' or named Fred' ... – PowerPoint PPT presentation

Number of Views:35

Avg rating:3.0/5.0

Slides: 30

Provided by: jeffch8

Category:

more less

Transcript and Presenter's Notes

Title: Conditionals and Boolean Expressions

1
Conditionals and Boolean Expressions
2
Overview

Flow Diagram
Boolean definition
Relational Operators
Testing equality of Strings
if statements
else statements
switch and Select statements

3
A Flow Diagram
Start
Blame it on someone else
Lay low and keep hidden
Did you break anything?
Yes
Yes
No
Have your parents asked about it?
Yes
Are you lying?
No
Are you passing your classes?
No
No
Ask for
Yes
End
4
The Boolean

A boolean is a something that resolves to true or
false
You can get booleans several different ways
Simple
Complex
These booleans will be used (later) to make
decisions to change your programs behavior

5
Relational Operators(for primitive data types)

Relational Operators
gt greater than
lt less than
equals ( in VB)
! Not (Not in VB)
! not equal (ltgt in VB)
gt greater than or equal
lt less than or equal
Notice that all of these return us a true or
false value!

6
Relational Operator Examples

Literal Example
5 gt 3 // true
6 ! 6 // false
true (4 lt 2) // false and redundant
c ! b // true
!false // true
Variable Example
int num1 5
short num2 7
boolean result num2 gt num1
//Note result is now true

7
String equality in Java

String is not a primitive type, so doesnt
work (most of the time)
Must use the .equals( ) function
For example, if you had
String myString Java
then
myString.equals (Coffee)
returns false and
myString.equals (Java)
returns true

8
and Operators

These operators check for multiple conditions
(AND in VB) needs both the left and the right
to be true in order to return true
AndAlso in VB shortcut
(OR in VB) needs either one (or both) to be
true to return true
Examples
( (6 gt 5) ( c b) ) // false
( (6 gt 5) ( 7 lt 9) ) // true
( (6 gt 5) ( c b) ) // true
( (6 gt 6) ( c b) ) // false

9
Now Lets Do Something!

Using the if statement, we can decide whether or
not to execute some code!
Has format
if (ltboolean valuegt)
// all the code thats in here will only execute
// if and only if the boolean above is true
// VB
If ltboolean valuegt Then
End If

10
if Example

int start 5
int end 19
if (start lt end )
System.out.println ( A )
// end if
System.out.println ( B )
Dim start As Integer 5
Dim end As Integer 19
If start lt end Then
Console.WriteLine (A)
End If
Console.WriteLine (B)

11
if Example

int start 5
int end 19
if (start lt end )
System.out.println ( A )
// end if
System.out.println ( B )
Dim start As Integer 5
Dim end As Integer 19
If start lt end Then
Console.WriteLine (A)
End If
Console.WriteLine (B)

Output
A
B
12
if Example(Part II)

int start 5
int end 19
if (start gt end )
System.out.println ( A )
// end if
System.out.println ( B )
Dim start As Integer 5
Dim end As Integer 19
If start gt end Then
Console.WriteLine (A)
End If
Console.WriteLine (B)

13
if Example(Part II)

int start 5
int end 19
if (start gt end )
System.out.println ( A )
// end if
System.out.println ( B )
Dim start As Integer 5
Dim end As Integer 19
If start gt end Then
Console.WriteLine (A)
End If
Console.WriteLine (B)

Output
B
14
The else statement

if has a counterpart the else statement
If the if clause didnt execute, the else clause
will!
Has format
if (ltboolean valuegt)
// statements that execute if the boolean is
true
else
// statements that execute if the boolean is
false
If ltboolean valuegt Then
// statements that execute if the boolean is
true
Else
// statements that execute if the boolean is
false
End If
Notice only one set of statements executes, no
matter what!

15
else Example

int start 5
int end 19
if (start gt end )
System.out.println ( A )
// end if
else
System.out.println ( B )
// end else
Dim start As Integer 5
Dim end As Integer 19
If start gt end Then
Console.Writeln ( A )
Else
Console.Writeln ( B )
End If

16
else Example

int start 5
int end 19
if (start gt end )
System.out.println ( A )
// end if
else
System.out.println ( B )
// end else
Dim start As Integer 5
Dim end As Integer 19
If start gt end Then
Console.Writeln ( A )
Else
Console.Writeln ( B )
End If

Output
B
17
else Example

int start 5
int end 19
if (start lt end )
System.out.println ( A )
// end if
else
System.out.println ( B )
// end else
Dim start As Integer 5
Dim end As Integer 19
If start lt end Then
Console.Writeln ( A )
Else
Console.Writeln ( B )
End If

18
else Example

int start 5
int end 19
if (start lt end )
System.out.println ( A )
// end if
else
System.out.println ( B )
// end else
Dim start As Integer 5
Dim end As Integer 19
If start lt end Then
Console.Writeln ( A )
Else
Console.Writeln ( B )
End If

Output
A
19
else ifs

Selecting one from many
As soon as one is true, the rest are not
considered
Has format
if (ltboolean valuegt)
else if (ltboolean valuegt)
else if (ltboolean valuegt)
else

If ltboolean valuegt Then stuff ElseIf ltboolean
valuegt Then stuff ElseIf ltboolean valuegt
Then stuff Else stuffEnd If
20
Combining into else ifs(Selecting one from
many)

int start 5 int middle 8 int end 19
if (start lt middle )
System.out.println ( A )
// end if
else if (start lt end)
System.out.println ( B )
// end else if
Dim start As Integer 5
Dim middle As Integer 8
Dim end As Integer 19
If start lt middle Then
Console.WriteLine ( A )
ElseIf start lt end
Console.WriteLine ( B )
End If

21
Combining into else ifs(Selecting one from
many)

int start 5 int middle 8 int end 19
if (start lt middle )
System.out.println ( A )
// end if
else if (start lt end)
System.out.println ( B )
// end else if
Dim start As Integer 5
Dim middle As Integer 8
Dim end As Integer 19
If start lt middle Then
Console.WriteLine ( A )
ElseIf start lt end
Console.WriteLine ( B )
End If

Output
A
22
else catch-all

int start 5 int middle 8 int end 19
if (start gt middle )
System.out.println ( A )
// end if
else if (start gt end)
System.out.println ( B )
// end else if
else
System.out.println ( C )
Dim start As Integer 5
Dim middle As Integer 8
Dim end As Integer 19
If start gt middle Then
Console.WriteLine ( A )
ElseIf start gt end
Console.WriteLine ( B )
Else

23
else catch-all

int start 5 int middle 8 int end 19
if (start gt middle )
System.out.println ( A )
// end if
else if (start gt end)
System.out.println ( B )
// end else if
else
System.out.println ( C )
Dim start As Integer 5
Dim middle As Integer 8
Dim end As Integer 19
If start lt middle Then
Console.WriteLine ( A )
ElseIf start lt end
Console.WriteLine ( B )
Else

Output
C
24
Switch/Select statements

Simplify the else-if statements for primitive
data types
Trying to find a match (or range in VB)
In Java, once a match is found, it will keep
going until it sees the break keyword (telling it
to stop)
Has format
switch (ltprimitive variablegt)
case ltvaluegt
case ltvaluegt

Select Case ltprimitive variablegt Case
ltvaluegt Case ltvaluegt To ltvaluegt End Select
25
Switch/Select Example