Pseudocode Algorithms Using
Sequence, Selection, and Repetition
Objectives
• In this chapter you will be able to:
• Develop solution algorithms to eight
typical programming problems using
sequence, selection, and repetition
constructs
Eight Solution Algorithms
• This chapter develops solution algorithms to eight
programming problems of increasing complexity
• All the algorithms will use a combination of sequence,
selection, and repetition constructs
• The algorithms have been designed to be interactive
or to process sequential files
1 Defining the Problem
• It is important that you divide the problem
into its three components:
– Input
– Output
– Processing
2 The Control Structures Required
• Once the problem has been defined, write
down the control structures (sequence,
selection, and repetition) that may be
needed, as well as any extra variables that
the solution may require
3 The Solution Algorithm
• Having defined the problem and
determined the required control
structures, devise a solution algorithm
and represent it using pseudocode
4 Desk Checking
• You will need to desk check each of the
developed algorithms with two or more
test cases
Example 6.1 Process Number Pairs
• Design an algorithm that will prompt for and
receive pairs of numbers from an operator at a
terminal and display their sum, product, and
average on the screen. If the calculated sum is
over 200, an asterisk is to be displayed beside the
sum. The program is to terminate when a pair of
zero values is entered
• A Defining diagram (shown on page 74)
Example 6.1 Process Number Pairs
• A Defining diagram
Input
Processing
Output
number1
Prompt for numbers
Sum
number2
Get numbers
product
Calculate sum
average
Calculate product
*
Calculate average
Display sum, product, average
Display *
Example 6.1 Process Number Pairs
• B Solution algorithm
Process_number_pairs
Set sum to zero
Prompt for number1, number2
Get number1, number2
DOWHILE NOT (number1=0 AND number2=0)
sum = number1+number2
product = number1*number2
average = sum/2
IF sum > 200 THEN
Display sum, *, product, average
ELSE
Display sum, product, average
ENDIF
Prompt for number1, number2
Get number1, number2
ENDDO
END
Example 6.2 Print Student Records
• A file of student records consists of ‘S’ records and
‘U’ records. An ‘S’ record contains the student’s
number, name, age, gender, address, and attendance
pattern; full-time (F/T) or part-time (P/T). A ‘U’ record
contains the number and name of the unit or units in
which the student has enrolled. There may be more
than one ‘U’ record for each ‘S’ record. Design a
solution algorithm that will read the file of student
records and print only the student’s number, name,
and address on a ‘STUDENT LIST’.
• A Defining Diagram (shown on page 75 of the text)
Example 6.2 Print Student Records
• A Defining Diagram
Input
Processing
Output
‘s’ records
Print headings
Heading line
• number
Read student records
Selected student records
• name
Select ‘s’ records
• number
• address
Print selected records
• name
• age
• gender
• attendance_pattern
‘u’ records
• address
Example 6.2 Print Student Records
•
B
Solution algorithm
Print_student_records
Print ‘STUDENT LIST’ headings
Read student record
DOWHILE move records exist
IF student record = “S” record THEN
Print student_number, name, address
ENDIF
Read student record
ENDDO
END
Example 6.3 Print Selected Students
• Design a solution algorithm that will read the
same student file as in Example 6.2, and produce
a report of all female students who are enrolled
part-time. The report is to be headed ‘PART TIME
FEMALE STUDENTS’ and is to show the student’s
number, name, address, and age
Example 6.3 Print Selected Students
A Defining Diagram
Input
Processing
Output
‘s’ records
Print headings
Heading line
• number
Read student records
Selected student records
• name
Select P/T female students
• number
• address
Print selected records
• name
• age
• address
• gender
• age
• attendance_pattern
‘u’ records
Example 6.3 Print Student Records
•
B
Solution algorithm – non-linear nested IF
Produce_part_time_female_list
Print ‘PART TIME FEMALE STUDENTS’ heading
Read student record
DOWHILE more records
IF student record = “S” record THEN
IF attendance_pattern = P/T THEN
IF gender = female THEN
Print student_number, name, address, age
ENDIF
ENDIF
ENDIF
Read student record
ENDDO
END
Example 6.3 Print Student Records
•
B Solution algorithm – nested and compound
IF statement
Produce_part_time_female_list
Print ‘PART TIME FEMALE STUDENTS’ heading
Read student record
DOWHILE more records
IF student record = “S” record THEN
IF attendance_pattern = P/T
AND gender = female THEN
Print student_number, name, address, age
ENDIF
ENDIF
Read student record
ENDDO
END
Example 6.3 Print Student Records
•
B
Solution algorithm – compound IF
Produce_part_time_female_list
Print ‘PART TIME FEMALE STUDENTS’ heading
Read student record
DOWHILE more records
IF student record = “S” record
AND attendance_pattern = P/T
AND gender = female THEN
Print student_number, name, address, age
ENDIF
Read student record
ENDDO
END
Example 6.4 Print and Total Selected
Students
• Design a solution algorithm that will read the
same student file as in Example 6.3 and produce
the same ‘PART TIME FEMALE STUDENTS’
report. In addition, you are to print at the end of
the report the number of students who have been
selected and listed, and the total number of
students on the file
• A Defining Diagram (shown on page 78)
Example 6.4 Print and Total Selected
Students
•
B
Control Structures Required
1. A DOWHILE loop to control the repetition
2. IF statements to select ‘S’, female, and P/T students
3. Accumulators for total_selected_students and
total_students
•
C Solution Algorithm
•
Examine the code listed on page 78 of the
textbook
Example 6.4 Print Student Records
•
B
Solution algorithm
Produce_part_time_female_list
Print ‘FEMALE PART-TIME STUDENTS’ heading
Set total_students to zero
Set total_selected_students to zero
Read student record
DOWHILE more records
IF student record = “S” record THEN
increment total_students
IF attendance_pattern = P/T
AND gender = female THEN
inrement total_selected_students
Print student_number, name, address, age
ENDIF
ENDIF
Read student record
ENDDO
Print total_students, total_selected_students
END
Example 6.5 Print Student Report
• Design an algorithm that will read the same
student file as in Example 6.4 and for each
student, print the name, number, and attendance
pattern from the ‘S’ records (student records) and
the unit number and unit name from the ‘U’
records (enrolled units records) as shown on
page 79 of the textbook. At the end of the report,
print the total number of students enrolled
• A Defining Diagram (shown on page 79)
Example 6.5 Print Student Report
•
B Control Structures Required
1. A DOWHILE loop to control the repetition
2. An IF statement to select ‘S’ or ‘U’ records
3. An accumulator for total_students
•
C Solution Algorithm
•
Examine the code illustrated on page 80 of the
textbook for this program problem
Example 6.6 Produce Sales Report
• Design a program that will read a file of sales
records and produce a sales report. Each record
in the file contains a customer’s number, name, a
sales amount, and a tax code. The tax code is to
be applied to the sales amount to determine the
sales tax due for that sale, as shown in the table
on page 80 of the textbook. The report is to print
a heading ‘SALES REPORT’, and detail lines
listing the customer number, name, sales amount,
sales tax, and the total amount owed
• A Defining Diagram (shown on page 81)
Example 6.6 Produce Sales Report
•
B Control Structures Required
1. A DOWHILE loop to control the repetition
2. A case statement to calculate the sales_tax
•
C Solution Algorithm
•
Examine the code illustrated on page 81
which is the solution for this program
problem
Example 6.7 Student Test Results
• Design a solution algorithm that will read a file of
student test results and produce a student test
grades report. Each test record contains the
student number, name, and test score (out of 50).
The program is to calculate for each student the
test score as a percentage and to print the
student’s number, name, test score (out of 50),
and letter grade on the report. The letter grade is
determined using the listing on page 81 of the
text
• A Defining Diagram (shown on page 82)
Example 6.7 Student test results
A Defining Diagram
Input
Processing
Output
student test record
Print headings
Heading line
• student_number
Read student records
Student details
• name
Calculate test percentage
• student_number
• test_score
Calculate letter grade
• name
Print student details
• test_score
• grade
Example 6.7 Student Test Results
•
B Control Structures Required
1. A DOWHILE loop to control the repetition
2. A formula to calculate the percentage
3. A linear nested IF statement to calculate the grade.
(The case construct cannot be used here, as CASE is
not designed to cater for a range of values.)
•
C Solution Algorithm
•
Refer to the code shown on page 82 of the
textbook
• B Solution algorithm
Print_student_results
Print ‘Student Test Grades’ heading
Read student record
DOWHILE NOT EOF
Percentage = test_score*2
IF percentage > 89 THEN
grade = A
ELSE IF percentage >89 THEN
grade = B
ELSE IF precentage > 79 THEN
grade = C
ELSE IF percentage > 69 THEN
grade = D
ELSE
grade = F
ENDIF
ENDIF
ENDIF
ENDIF
Print studet_number, name, test_score
Read student record
ENDDO
END
Example 6.8 Gas Supply Billing
• Refer to the background of the Domestic Gas Supply
company on page 83 of the text. Design a solution
algorithm that will read the customer usage file, calculate
the amount owing for gas usage for each customer, and
print a report listing each customer’s number, name,
address, gas usage, and the amount owing. Read the
remainder of the problem specification on page 83 and at
the end of the report, print the total number of customers
and the total amount owed to the company
• A Defining Diagram (shown on page 83)
Example 6.8 Gas Supply Billing
•
B Control Structures Required
1. A DOWHILE loop to control the repetition
2. An IF statement to calculate the amount_owing
3. Accumulators for total_customers and
total_amount_owing
•
C Solution Algorithm
•
Examine the code shown on page 84 of the
textbook, which shows the pseudocode for this
problem
Summary
•
This chapter developed solution algorithms to
eight typical programming problems
•
The approach to all eight problems followed the
same pattern:
1. The problem was defined, using a defining diagram
2. The control structures required were written down,
along with any extra variables required
3. The solution algorithm was produced, using
pseudocode and the three basic control structures:
sequence, selection, and repetition