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Relational Expressions

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using namespace std; int main() { // Begin Main Function. int i = 2; int j = 3; ... NOTE: In a conditional expression, you need to have a double equals sign ... – PowerPoint PPT presentation

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Title: Relational Expressions

1
Chapter 5

Relational Expressions
May the computer gods have mercy

2
Decision Making in Programs

Almost all programs have branching structures
which require decision making.
A flowchart maps the decisions a program is to
make and the path down which each decision leads.
A flowchart uses different shapes to show
different actions

3
(No Transcript)
4
Process
5
Process
Selectionor Decision
6
Representing True and False in C

Computers make complex branching decisions by
making simple comparisons.
If a comparison is TRUE, C returns a 1 to
represent true.
If a comparison is FALSE, C returns a 0 to
represent false.

7
Relational Operators

C provides the following relational operators
for making comparisons.
Operator Meaning
equal to
gt greater than
lt less than
gt greater than or equal to
lt less than or equal to
! not equal to

8
Logical Operators

C provides 3 logical operators in case more
than one comparison needs to be made at one time.
Operator Meaning
and
or
! not

9
Example I

Example 1 covers logical operators

// program1.cpp
// Jason Long
// Class Example
include ltiostreamgt
using namespace std
int main()
// Begin Main Function
int i 2
int j 3
cout ltlt (i 2) ltlt endl
cout ltlt (i 1) ltlt endl
cout ltlt (j gt i) ltlt endl
cout ltlt (j lt 3) ltlt endl
cout ltlt (j ! i) ltlt endl

// program1.cpp
// Jason Long
// Class Example
include ltiostreamgt
using namespace std
int main()
// Begin Main Function
int i 2
int j 3
cout ltlt (i 2) ltlt endl
cout ltlt (i 1) ltlt endl
cout ltlt (j gt i) ltlt endl
cout ltlt (j lt 3) ltlt endl
cout ltlt (j ! i) ltlt endl

12
Comment Lines
13

// program1.cpp
// Jason Long
// Class Example
include ltiostreamgt
using namespace std
int main()
// Begin Main Function
int i 2
int j 3
cout ltlt (i 2) ltlt endl
cout ltlt (i 1) ltlt endl
cout ltlt (j gt i) ltlt endl
cout ltlt (j lt 3) ltlt endl
cout ltlt (j ! i) ltlt endl

14
Libraries
15

// program1.cpp
// Jason Long
// Class Example
include ltiostreamgt
using namespace std
int main()
// Begin Main Function
int i 2
int j 3
cout ltlt (i 2) ltlt endl
cout ltlt (i 1) ltlt endl
cout ltlt (j gt i) ltlt endl
cout ltlt (j lt 3) ltlt endl
cout ltlt (j ! i) ltlt endl

16
Main Function
17

// program1.cpp
// Jason Long
// Class Example
include ltiostreamgt
using namespace std
int main()
// Begin Main Function
int i 2
int j 3
cout ltlt (i 2) ltlt endl
cout ltlt (i 1) ltlt endl
cout ltlt (j gt i) ltlt endl
cout ltlt (j lt 3) ltlt endl
cout ltlt (j ! i) ltlt endl

18
Variables
19

// program1.cpp
// Jason Long
// Class Example
include ltiostreamgt
using namespace std
int main()
// Begin Main Function
int i 2
int j 3
cout ltlt (i 2) ltlt endl
cout ltlt (i 1) ltlt endl
cout ltlt (j gt i) ltlt endl
cout ltlt (j lt 3) ltlt endl
cout ltlt (j ! i) ltlt endl

20
cout line 1

cout ltlt (i 2) ltlt endl
(i 2)
This is a conditional expression.
It is asking if i is equal to 2.
NOTE In a conditional expression, you need to
have a double equals sign
If you have the following expression (i 2) this
will set the variable i to the number 2
This line will print the number 1. This means
the expression is True because i is equal to 2.

// program1.cpp
// Jason Long
// Class Example
include ltiostreamgt
using namespace std
int main()
// Begin Main Function
int i 2
int j 3
cout ltlt (i 2) ltlt endl
cout ltlt (i 1) ltlt endl
cout ltlt (j gt i) ltlt endl
cout ltlt (j lt 3) ltlt endl
cout ltlt (j ! i) ltlt endl

22
cout line 2

cout ltlt (i 1) ltlt endl
(i 1)
This line will print the number 0. This means
the expression is False because i does not equal
to 1.

// program1.cpp
// Jason Long
// Class Example
include ltiostreamgt
using namespace std
int main()
// Begin Main Function
int i 2
int j 3
cout ltlt (i 2) ltlt endl
cout ltlt (i 1) ltlt endl
cout ltlt (j gt i) ltlt endl
cout ltlt (j lt 3) ltlt endl
cout ltlt (j ! i) ltlt endl

24
The other cout line

cout ltlt (j gt i) ltlt endl
This line will print the number 1.
cout ltlt (j lt 3) ltlt endl
This line will print the number 1.
cout ltlt (j ! i) ltlt endl
This line will print the number 1. ! means not
equal.

// program1.cpp
// Jason Long
// Class Example
include ltiostreamgt
using namespace std
int main()
// Begin Main Function
int i 2
int j 3
cout ltlt (i 2) ltlt endl
cout ltlt (i 1) ltlt endl
cout ltlt (j gt i) ltlt endl
cout ltlt (j lt 3) ltlt endl
cout ltlt (j ! i) ltlt endl

26
Return 0

Ends the program

27
Example 2

Bool data type
Bool data type only store two possible values
1 for True
0 for False
Variable
We will expand on Example 1

// program1.cpp
// Jason Long
// Class Example
include ltiostreamgt
using namespace std
int main()
// Begin Main Function
int i 2
int j 3
bool the_bool
the_bool (j i)
cout ltlt (i 2) ltlt endl
cout ltlt (i 1) ltlt endl

// program1.cpp
// Jason Long
// Class Example
include ltiostreamgt
using namespace std
int main()
// Begin Main Function
int i 2
int j 3
bool the_bool
the_bool (j i)
cout ltlt (i 2) ltlt endl
cout ltlt (i 1) ltlt endl

30
New Lines
31

// program1.cpp
// Jason Long
// Class Example
include ltiostreamgt
using namespace std
int main()
// Begin Main Function
int i 2
int j 3
bool the_bool
the_bool (j i)
cout ltlt (i 2) ltlt endl
cout ltlt (i 1) ltlt endl

32
The bool variable

bool the_bool
The data type is bool
Remember only stores true or false
The name of the variable is the_bool

// program1.cpp
// Jason Long
// Class Example
include ltiostreamgt
using namespace std
int main()
// Begin Main Function
int i 2
int j 3
bool the_bool
the_bool (j i)
cout ltlt (i 2) ltlt endl
cout ltlt (i 1) ltlt endl

34
Setting the variable

the_bool (j i)
(j i)
Does j I
NoIts false
the_bool will equal 0

// program1.cpp
// Jason Long
// Class Example
include ltiostreamgt
using namespace std
int main()
// Begin Main Function
int i 2
int j 3
bool the_bool
the_bool (j i)
cout ltlt (i 2) ltlt endl
cout ltlt (i 1) ltlt endl

36
Printing the the_bool variable
37
Combining More than Two Comparisons

You can use logical operators to combine more
than two comparisons.
ok_to_ride (height_in_inches gt 45
!back_trouble
!heart_trouble)

38
Order of Logical Operations

You can mix logical operators in statements as
long as you understand the order in which the
logical operators will be applied.
The not operator (!) is applied first,
! means not
Then the and operator ()
means and
Finally the or operator ()
(shift \ key) means or

39
Example 3

Combining More than Two Comparisons
Again, we will expand on Example 1

// program1.cpp
// Jason Long
// Class Example
include ltiostreamgt
using namespace std
int main()
// Begin Main Function
int i 2
int j 3
cout ltlt (i 2) ltlt endl
cout ltlt (j 2) ltlt endl
cout ltlt ((i 2) (j 2)) ltlt endl
cout ltlt ((i 2) (j 2)) ltlt endl

// program1.cpp
// Jason Long
// Class Example
include ltiostreamgt
using namespace std
int main()
// Begin Main Function
int i 2
int j 3
cout ltlt (i 2) ltlt endl
cout ltlt (j 2) ltlt endl
cout ltlt ((i 2) (j 2)) ltlt endl
cout ltlt ((i 2) (j 2)) ltlt endl

42
The and Evaluation

In an expression like
in_range (i gt 0 i lt 11)
If the first part of the comparison is false,
there is no need to check the second half so the
program will skip it.
If either i gt 0 is false or i lt 11 is false, the
whole comparison would be false.

// program1.cpp
// Jason Long
// Class Example
include ltiostreamgt
using namespace std
int main()
// Begin Main Function
int i 2
int j 3
cout ltlt (i 2) ltlt endl
cout ltlt (j 2) ltlt endl
cout ltlt ((i 2) (j 2)) ltlt endl
cout ltlt ((i 2) (j 2)) ltlt endl

44
The or Evaluation

In an expression like
in_range (i gt 0 i lt 11)
If either part of the comparison is true, the who
comparison is true.

45
Introduction to Selection Structures

Sequence structures execute statements one after
another without changing the flow of the program.
The structures that make decisions in C
programs are called selection structures.
When a decision is made in a program, a selection
structure controls the flow of the program based
on the decision.

46
Using if

The if structure is in most if not all
programming languages.
The expression that makes the decision is called
the control expression.
Example
if (i 3)
cout ltlt "The value of i is 3 ltlt endl

47
Using if/else

The if/else structure is sometimes called a
two-way selection structure.
Using if/else, one block of code is executed if
the control expression is true and another block
is executed if the control expression is false.

48
Example of if/else

if (i 4)
cout ltlt "number is 4" ltlt endl
else
cout ltlt "number not 4" ltlt endl

49
Example 4

Logical Example
Using a flow chart

50
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51
Run through the flow chart
52
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53
Asking the user to enter in a number
54
Asking the user to enter in a number
The variable where the number will be stored
55
Asking the user to enter in a number
The variable where the number will be stored
The IF statement condition statement
56
Asking the user to enter in a number
What will be processed if the condition is true
The variable where the number will be stored
The IF statement condition statement
57
Asking the user to enter in a number
What will be processed if the condition is True
The variable where the number will be stored
The IF statement condition statement
What will be processed if the condition is False
58
Use the flowchart to create the program