Introduction to Flowcharting

This appendix provides a brief introduction to flowcharting. It includes example flowcharts
for programs that appear in Chapters 1 through 6. In addition, a complete lesson
on flowcharting is included on the Student CD. The lesson is stored in a PowerPoint file
named
Flowcharting.ppt
.
A flowchart is a diagram that depicts the “flow” of a program. It contains symbols that
represent each step in the program. The figure shown here is a flowchart for Program 1-1,
the pay-calculating program in Chapter 1.
START
END
Display message
”How many
hours did
you work?”
Display message
”How much
do you get
paid per hour?”
Multiply hours
by payRate.
Store result in
grossPay.
Read hours
Read payRate
Display
grossPay
2
Appendix D: Introduction to Flowcharting
Notice there are three types of symbols in this flowchart: rounded rectangles (representing
terminal points), parallelograms (representing input/output operations), and a rectangle
(representing a process).
The rounded rectangles, or terminal points, indicate the flowchart’s starting and ending
points. The parallelograms designate input or output operations. The rectangle depicts a
process such as a mathematical computation, or a variable assignment. Notice that the
symbols are connected with arrows that indicate the direction of program flow.
Connectors
Sometimes a flowchart is broken into two or more smaller flowcharts. This is usually done
when a flowchart does not fit on a single page, or must be divided into sections. A connector
symbol, which is a small circle with a letter or number inside it, allows you to connect
two flowcharts.
In the figure below, the A connector indicates that the second flowchart segment begins
where the first flowchart segment ends.
Terminal Input/Output Processes
Operations
A
END
START A
A
Appendix D: Introduction to Flowcharting
3
Flowchart Structures
There are four general flowchart structures:
•
Sequence
•
Decision
•
Repetition
•
Case
A sequence structure is a series of actions or steps, performed in order. The flowchart for
the pay-calculating program is an example of a sequence structure. The following flowchart
is also a sequence structure. It depicts the steps performed in Program 2-20, from
Chapter 2.
Flowchart for Program 2-20
The following flowchart, which is another sequence structure, depicts the steps performed
in Program 3-15 (from Chapter 3). Notice the use of connector symbols to link the two
flowchart segments.
END
START
Display
Total Pay
Calculate Total
Wages as Regular
Wages plus
Overtime Wages.
Calculate Regular
Wages as Base
Pay times
Regular Hours.
Calculate Overtime
Wages as
Overtime Pay
times Overtime
Hours.
4
Appendix D: Introduction to Flowcharting
Flowchart for Program 3–15
The Decision Structure
In a decision structure, one of two possible actions is performed, depending on a condition.
In a decision structure, a new symbol, the diamond, represents a yes/no question. If
the answer to the question is “yes,” the program flow follows one path. If the answer to
the question is “no,” the program flow follows another path. The following figure shows
the general form of a decision structure.
START
END
Ask user to enter
beginning
inventory value
for all three stores.
Store begInv
in store1,
store2, and
store3.
Subtract sold
from store1.
Read begInv.
Read sold.
Ask user to enter
number of widgets
sold at Store 1.
A
A
Ask user to enter
number of widgets
sold at Store 2.
Subtract sold
from sold2.
Subtract sold
from store3.
Read sold.
Read sold.
Ask user to enter
number of widgets
sold at Store 3.
Display inventory
values for all
three stores.
Appendix D: Introduction to Flowcharting
5
In the following flowchart segment, the question “is x < y?” is asked. If the answer is
“no,” then process A is performed. If the answer is “yes,” then process B is performed.
The following flowchart depicts the logic of Program 4-8, from Chapter 4. The decision
structure shows that one of two possible messages is displayed on the screen, depending
on the value of the expression
number % 2
.
NO YES
NO
Process A Process B
YES
x < y?
6
Appendix D: Introduction to Flowcharting
Flowchart for Program 4–8
The Case Structure
In a case structure, one of several possible actions is taken, depending on the contents of a
variable. The following flowchart segment shows the general form of a case structure.
The following flowchart depicts the logic of Program 4–31, which is also from Chapter 4.
One of 4 possible paths is followed, depending on the value stored in the variable
feedGrade
.
NO
Display
”Number is
odd.”
number % 2
equal to 0?
Read number.
Ask user to enter
an integer.
Display
”Number is
even.”
YES
START
END
Appendix D: Introduction to Flowcharting
7
Flowchart for Program 4–31
Repetition Structures
A repetition structure represents part of the program that repeats. This type of structure
is commonly known as a loop. The following figure shows an example of a repetition
structure.
Notice the use of the diamond symbol. A repetition structure tests a condition, and if the
condition exists, it performs an action. Then it tests the condition again. If the condition
still exists, the action is repeated. This continues until the condition no longer exists. In
the flowchart segment above, the question “is x < y?” is asked. If the answer is yes, then
Start
Ask the user to
enter the desired
feed grade.
Read input into
feedGrade.
End
'a'
'A'
'b'
'B'
'c'
'C' Other
case feedGrade
Display "30 cents
per pound".
Display "20 cents
per pound".
Display "15 cents
per pound".
Display "That is an
invalid choice".
YES
x < y? Process A
8
Appendix D: Introduction to Flowcharting
Process A is performed. The question “is x < y?” is asked again. Process A is repeated as
long as x is less than y. When x is no longer less than y, the repetition stops and the structure
is exited.
There are two forms of repetition structure: pre-test and post-test. A pre-test repetition
structure tests its condition
before
it performs an action. The flowchart segment above
shows a pre-test structure. Notice that Process A does not execute at all if the condition “x
< y” is not true. The pre-test repetition structure is coded in C++ as a
while
loop.
A post-test repetition structure tests its condition
after
it performs an action. This type of
loop always performs its action at least once. The following flowchart segment shows an
example.
The post-test repetition structure is coded in C++ as a
do-while
loop.
The following flowchart depicts the logic of Program 5-6, which appears in Chapter 5.
Flowchart for Program 5-6
YES
NO
Process A
x < y?
START
number = 1.
Display Table
Headings.
Display number
and number
Squared.
number <=
10?
YES
NO
Add 1 to number.
END
Appendix D: Introduction to Flowcharting
9
Modules
A program module (such as a function in C++) is represented by the special symbol shown
below:
The position of the module symbol indicates the point the module is executed, as shown in
the following figure:
A separate flowchart can then be constructed for the module. The following figure shows
a flowchart for Program 6-19 from Chapter 6. The
getBasePay
and
getOvertimePay
modules appear as separate flowcharts.
START
END
Read Input.
Call calc_pay
function.
Display results.
10
Appendix D: Introduction to Flowcharting
Flowchart for Program 6-19
Start
Ask the user to
enter the number
of hours worked.
hours >
BASE_HOURS?
Call
getBasePay
Yes
Call
getOvertimePay
Calculate total pay.
No
Display base pay,
overtime pay, and total
pay.
End
Start of
getBasePay
No hours > Yes
BASE_HOURS?
basePay =
BASE_HOURS *
PAY_RATE
basePay =
hoursWorked *
PAY_RATE
End of
getBasePay
Start of
getOvertimePay
No hours > Yes
BASE_HOURS?
overtimePay = (hoursWorked
- BASE_HOURS) *
PAY_RATE *
OT_MULTIPLIER
overtimePay = 0.0
End of
getOvertimePay