A High-Level Model For Software
Development
What is involved in the process of
designing, writing and maintaining
computer programs?
What are some ways that an algorithm
can be specified?
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What Is Computer Science?
Review: Solving problems with the computer
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A Model For Creating Computer Software
Specify the problem
Determine how to solve the problem
Implement the solution
Maintenance of the solution
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Specifying The Problem
Determine what problem will be solved by the computer
Verify the problem
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Determine How To Solve The Problem
Specify the algorithm
- Can be done in many ways
- e.g., flowcharts, spreadsheets (more to come later in this section of
notes)
- Implementation independent!
Check the algorithm
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Implement The Design
Translating the high level algorithm to an actual programming
language (e.g., Pascal)
Test the program
This step is covered in the balance of this course (and the next
course, CPSC 233)
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Maintaining The Design
Modify the program according to changing needs and to
address problems (software bugs)
Includes the application of techniques for good design
(Software Engineering).
Some in CPSC 233 (more in CPSC 333)
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What You Now Know: A Model For Creating
Computer Software
Specify the problem
Determine how to solve the problem (algorithm)
Implement the solution
Maintenance of the solution
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What Is An Algorithm?
The steps needed to solve a problem
Characteristics
• Specific
• Unambiguous
• Language independent
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Ways Of Specifying The Algorithm
Pseudo-code
Flowcharts
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Pseudo-Code
Employs 'programming-like' statements to depict the algorithm
No standard format (language independent)
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Pseudo-Code Statements
Display
Enter
Action
Decision making
Repetition
Statements are carried out in order
Example: Calling up a friend
1) Look up telephone number
2) Punch in telephone number
3) Wait for someone to answer
:
:
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Variables
Are used with pseudo-code statements
Symbols (typically an alphabetic string e.g,, x, num, num1) used
to store values
The value stored can change during the algorithm
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Constants
Are used with pseudo-code statements
They are values that cannot be changed
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Display
Used to show information
General format:
Line of text: Display 'Message'
Variable:
Display Name of variable
Mixed display: Separate each item to be displayed with a comma
Example
Display 'Available credit limit $', limit
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Enter
Used to get information
Information is stored in a variable
General format:
Enter: Name of variable
Example:
Enter userName
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Pseudo-Code: Action
For computer programs it's usually an assignment statement (sets
a variable to some value)
General form:
Variable = arithmetic expression
Example:
x=2
x=x+1
a=b*c
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Pseudo-Code: Decision Making
If-then
General form:
if (condition is met) then
statement(s)
Example:
if temperature < 0 then
wear a jacket
If-then-else
General form:
if (condition is met) then
statement(s)
else
statements(s)
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Pseudo-Code: Decision Making (2)
Example:
if (at work) then
Dress formally
else
Dress casually
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Pseudo-Code: Decision Making (3)
Types of conditions
Symbol
Greater than
>
Greater than or equal to
≥
Less than
<
Less than or equal to
≤
Equal to
=
Not equal to
≠
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Pseudo-Code: Repetition
repeat-until
while-do
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Pseudo-Code: Repetition (2)
repeat-until
Repeat at least once (check if condition is met after statement(s))
General form:
repeat
statement(s)
until (condition is met)
Example:
repeat
Go up to buffet table
until full
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Pseudo-Code: Repetition (3)
while-do
Repeat zero or more times (check if condition is met before statement(s))
General form:
while (condition is met) do
statement(s)
Example:
while students ask questions do
Answer questions
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Pseudo-Code: Fast Food Example
Use pseudo-code to specify the algorithm for a person who ordering food at a
fast food restaurant. At the food counter, the person can either order or not
order the following items: a burger, fries and a drink. After placing her order
the person then goes to the cashier.
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Pseudo-Code: Fast Food Example
Approach counter
If want burger then
Order burger
If want fries then
Order fries
If want drink then
Order drink
Pay cashier
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Pseudo-Code: Grade Tabulator Example
Use pseudo-code to specify the algorithm for a grade tabulation program. The
program will ask the instructor to enter in a percentage value for each student.
Based on this value the program will determine if the student passed the
course or not:
• If the percentage is 50% or greater then the student passed the course and the
message 'Student receives course credit' will appear.
• Otherwise, if the percentage is below 50%, then the student failed the course and
the message 'Student will not receive course credit' will appear.
As the instructor is entering grades, the program will automatically track the
number of students who passed the course and the number of students that did
not. The instructor indicates to the program that she has finished entering the
grades by entering negative percentage (e.g., -1%) at which time the program
displays the total number of students that passed and total that did not pass
and it then ends execution.
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Pseudo-Code: Grade Tabulator Example
pass = 0
fail = 0
Display 'Enter percentage for student (negative percentage to end): '
Enter percentage
While Percentage ≥ 0 do
If (percentage ≥ 50) then
Display 'Student receives course credit'
pass = pass + 1
Else
Display 'Student will not receive course credit'
fail = fail + 1
Display 'Enter percentage for student (negative percentage to end): '
Enter percentage
Display 'Number of students that passed: ', pass
Display 'Number of students that failed: ', fail
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Summary Of Pseudo-Code Statements
Statement
Purpose
Display
Enter
Action
Decision
Repetition
Display information
Get information
Perform an activity (not covered by the other statements)
Choose between different alternatives
Perform a step multiple times
Variables are used in conjunction with these statements to store information.
Constants may be used to represent a value that does not ever change.
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Basic Flowchart Elements
Terminator
Action
Input
Output
Off page
Connector
Decision
Arrow
c
Variables and
constants
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Flowchart: Fast Food Example
Draw a flowchart to outline the algorithm for a person who ordering food at a
fast food restaurant. At the food counter, the person can either order or not
order the following items: a burger, fries and a drink. After placing her order
the person then goes to the cashier.
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Flowchart: Fast Food Example
Approach
counter
Want
Y
Order
burger
Y
Order
fries
Y
Order
drink
burger?
N
Want
fries?
N
Want
Drink?
N
Pay
cashier
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Flowchart: Grade Tabulator Example
Use a flowchart to specify the algorithm for a grade tabulation program. The
program will ask the instructor to enter in a percentage value for each student.
Based on this value the program will determine if the student passed the
course or not:
• If the percentage is 50% or greater then the student passed the course and the
message 'Student receives course credit' will appear.
• Otherwise, if the percentage is below 50%, then the student failed the course and
the message 'Student will not receive course credit' will appear.
As the instructor is entering grades, the program will automatically track the
number of students who passed the course and the number of students that did
not. The instructor indicates to the program that she has finished entering the
grades by entering negative percentage (e.g., -1%) at which time the program
displays the total number of students that passed and total that did not pass
and it then ends execution.
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Flowchart: Grade Tabulator Example
Begin
pass = 0
fail = 0
'Enter percentage for student
(negative to end'): '
Percentage
1
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Flowchart: Grade Tabulator Example (2)
1
6
Percentage ≥ 0?
N
2
Y
Percentage ≥ 50?
N
3
Y
4
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Flowchart: Grade Tabulator Example (3)
3
'Student will not receive course credit'
fail = fail + 1
5
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Flowchart: Grade Tabulator Example (4)
4
'Student receives course credit'
pass = pass + 1
5
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Flowchart: Grade Tabulator Example (5)
5
'Enter percentage for student
(negative to end'): '
Percentage
6
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Flowchart: Grade Tabulator Example (6)
2
'Number of students that failed: ', fail
'Number of students that passed: ', pass
End
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Summary
What are the major steps involved in creating software
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•
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Specification
Design
Implementation
Maintenance
How to layout out an algorithm using flowcharts and pseudocode
What are the basic elements of algorithms
•
•
•
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Input
Output
Decision-Making
Repetition
Action
Variables and constants
James Tam