Chapter 1
Program Design
Objectives
• In this chapter you will be able to:
• Describe the steps in the program development
process
• To introduce current program design methodology
• Introduce procedural and object-oriented
programming
• Introduce algorithms
• Describe program data
Simple Program Design, Fourth Edition
Chapter 1
2
Program Design
•
Most good programs require good planning
before they are written. This is called Program
Design.
Simple Program Design, Fourth Edition
Chapter 1
3
Steps in Program Development
The steps in program design are similar to the steps in problem
solving. They are:
1. Define the problem
2. Outline the solution
3. Develop the outline into an algorithm
4. Test the algorithm for correctness
5. Code the algorithm into a specific programming language
6. Run the program on the computer
7. Document and maintain the program
Simple Program Design, Fourth Edition
Chapter 1
4
Steps in Program Development
1 Define the Problem
To help with initial analysis, the problem should be
divided into three separate components:
– the inputs - What information is given to you
to use to solve the problem?
– the outputs - What will the solution of the
problem, look like
– the processing steps - What calculations
(processes), will be used to change the input
information into the desired output?
•
Tool: Defining diagram
Simple Program Design, Fourth Edition
Chapter 1
5
2 Outline the Solution
• Break the problem into the steps of what must be
done to solve the problem:
– The major processing steps involved
– The major subtasks (if any)
– The user interface (if any)
– The major control structures (e.g. repetition loops)
– The major variables and record structures
– The mainline logic
Tools: Hierarchy or Structure charts
Simple Program Design, Fourth Edition
Chapter 1
6
3 Develop the Outline into an Algorithm
• The solution outline developed in Step 2 is
expanded into an algorithm:
• It should list all the steps that need to be done, in
the correct order they need to be done in.
Tools: Pseudocode, Flowcharts, NassiSchneiderman diagrams
Simple Program Design, Fourth Edition
Chapter 1
7
4 Test the Algorithm for Correctness
•
In this step, you pretend to be a computer and execute the steps
in the algorithm. This is called "Desk Checking."
• This step is one of the most important in the development
of a program, and yet it is the step most often forgotten
• The main purpose of desk checking the algorithm is to
identify major logic errors early, so that they may be easily
corrected
Simple Program Design, Fourth Edition
Chapter 1
8
5 Code the Algorithm into a Specific Programming
Language
• Once the algorithm, or complete outline works
correctly, you need to translate the algorithm into
a computer language that your computer
understands.
– This is only 5 to 10% of the total programming process!
Simple Program Design, Fourth Edition
Chapter 1
9
6 Run the Program on the Computer
• This step uses a program compiler and programmerdesigned test data to machine test the code for syntax
errors (at compile time) and logic errors (at run time)
•
You enter the program into the computer's memory, enter the
input data, and have the computer execute the program. If you get
the correct answer to the problem, the program works! Otherwise,
look for errors in the program and try again.
Simple Program Design, Fourth Edition
Chapter 1
10
7 Document and Maintain the Program
• Warning! The Documentation of the program
started by writing down "What is the Problem!" It
continues through each step of the design
process.
• Documentation involves:
– external documentation
– internal documentation that may have been coded in the
program
Simple Program Design, Fourth Edition
Chapter 1
11
Program Design Methodology
• Recently, a number of different
approaches to program design have
emerged, the most common being:
– Procedure-driven
– Event-driven
– Data-driven
Simple Program Design, Fourth Edition
Chapter 1
12
Procedure-Driven Program Design
• The procedure-driven approach to
program design is based on the idea that
the most important feature of a program is
‘what’ it does – that is, its processes or
functions
Simple Program Design, Fourth Edition
Chapter 1
13
Procedure-Driven Program Design
Example
• A program to execute a sales order may
be divided into:
– order entry module
– data verification module
– Inventory update module
Simple Program Design, Fourth Edition
Chapter 1
14
Procedure-Driven Program Design
• In procedure-driven programming, the sequence of
operations for an application is determined by a
central controlling program (e.g., a main procedure).
– The program determines in advance what will be done
and in which order. The program starts at the beginning,
occasionally calls subroutines
Simple Program Design, Fourth Edition
Chapter 1
15
Event-Driven Program Design
• The event-driven approach to program
design is based on the idea that an event
or interaction with the outside world can
cause a program to change from one
known state to another
• In event-driven programming the code responds
to a system-generated event, such as a buttonpush or a clock cycle.
Simple Program Design, Fourth Edition
Chapter 1
16
Data-Driven Program Design
• The data-driven approach to program design is
based on the idea that the data in a program is
more stable than the processes involved
• It begins with an analysis of the data and the
relationships between the data, in order to
determine the fundamental data structures
• The choice between procedure-driven, eventdriven, or data-driven program design
methodologies is usually determined by the
selection of a programming language
Simple Program Design, Fourth Edition
Chapter 1
17
Procedural versus Object-Oriented
Programming
• Procedural programming is based on a structured, topdown approach to writing effective programs
• In the top-down development of a program design:
1. a general solution to the problem is outlined first
2. the general solution is then broken down gradually into more
detailed steps until finally the most detailed levels have been
completed
Simple Program Design, Fourth Edition
Chapter 1
18
Modular Design
• Procedural programming also
incorporates the concept of modular
design, which involves grouping tasks
together because they all perform the
same function
• Modular design is connected directly to
top-down development
Simple Program Design, Fourth Edition
Chapter 1
19
Object-Oriented Programming
• Object-oriented programming is also
based on decomposing the problem;
however, the primary focus is on the
things that make up the program
Simple Program Design, Fourth Edition
Chapter 1
20
Quick Quiz
1. Name and define the second step in program
development.
•
ANSWER: Outline the solution- is the initial
outline usually in a rough draft of the solution
which may include: major processing steps
involved, major subtasks, user interface, major
control structures, major variables and record
structures, and the mainline logic.
Simple Program Design, Fourth Edition
Chapter 1
21
Quick Quiz
2. The __________-driven approach to
programming is based on the idea that an
interaction with the outside world can cause a
program to change from one known state to
another.
•
ANSWER: event
Simple Program Design, Fourth Edition
Chapter 1
22
Quick Quiz
3. The choice between procedure-driven, eventdriven, or data-driven program design
methodologies is usually determined by the
selection of a(n) __________.
•
ANSWER: programming language
Simple Program Design, Fourth Edition
Chapter 1
23
Quick Quiz
4. __________ programming is based on a
structured, top-down approach to writing
effective programs.
•
ANSWER: Procedural
Simple Program Design, Fourth Edition
Chapter 1
24
Quick Quiz
5. ___________ programming is also based on
decomposing the problem; however, the primary
focus is on the things that make up the program.
•
ANSWER: Object-oriented
Simple Program Design, Fourth Edition
Chapter 1
25
An Introduction to Algorithms and
Pseudocode
• A program must be systematically and
properly designed before coding begins
• This design process results in the
construction of an algorithm
Simple Program Design, Fourth Edition
Chapter 1
26
What Is an Algorithm?
• An algorithm is like a recipe: it lists the steps
involved in accomplishing a task
• It can be defined in programming terms as a
set of detailed, unambiguous and ordered
instructions developed to describe the
process necessary to produce the desired
output from a given input
Simple Program Design, Fourth Edition
Chapter 1
27
What Is Pseudocode?
• Pseudocode, flowcharts, and Nassi-Schneiderman
diagrams are all popular ways of representing algorithms
• Flowcharts and Nassi-Schneiderman diagrams are covered
in Appendices 1 and 2, while pseudocode has been chosen
as the primary method of representing an algorithm
because it is easy to read and write and allows the
programmer to concentrate on the logic of the problem
• Pseudocode is really structured English
– It is English that has been formalized and abbreviated to look
like high-level computer languages
Simple Program Design, Fourth Edition
Chapter 1
28
Understanding Program Data
•
Information processed by the computer is data.
1. a single variable, such as an integer or a
character, or
2. a group item (sometimes called an aggregate),
such as an array, or a file
Simple Program Design, Fourth Edition
Chapter 1
29
Variables, Constants, and Literals
• A variable is the name given to a collection of
memory cells, designed to store a particular
data item
• It is called a variable because the value
stored in those memory cells may change or
vary as the program executes
• Example
total = num1 + num2
Simple Program Design, Fourth Edition
Chapter 1
30
Variables, Constants, and Literals
• A constant is a data item with a name and a
value that remain the same during the
execution of the program
• A literal is a constant whose name is the
written representation of its value
Simple Program Design, Fourth Edition
Chapter 1
31
Data Types
• At the beginning of a program, the
programmer must clearly define the form
or type of data to be collected
• The data types can be elementary data
items or data structures
Simple Program Design, Fourth Edition
Chapter 1
32
Elementary Data Items
• An elementary data item is one containing a single variable
that is always treated as a unit
• The most common elementary data types are:
— Integer: holds a whole number
— Real: holds a decimal value, or is a number with a fractional part
— Character: holds a symbol such as a through z, 1 through 9, or !,
@,#,$,%,^, etc
— Boolean: holds either a value of true or false.
Simple Program Design, Fourth Edition
Chapter 1
33
Data Structures
• A data structure is an aggregate of other data items
• The data items that it contains are its components, which
may be elementary data items or another data structure
• The most common data structures are:
— Records: a collection of data items or field related to each
other
— File: a collection of records
— Array: a collection of data items, all of the same type!
— String: a collection of zero or more characters.
Simple Program Design, Fourth Edition
Chapter 1
34
Files
• There are two different methods of storing data
on files:
– Sequential or text files
– Direct or random-access files
Simple Program Design, Fourth Edition
Chapter 1
35
Data Validation
• Data should always undergo a validation
check before it is processed by a program
• Different types of data require different
checks – for example:
– Correct type
— Correct range
– Correct length
— Completeness
– Correct date
Simple Program Design, Fourth Edition
Chapter 1
36
Summary
•
The steps in program development were introduced and
briefly described below:
1. Define the problem
2. Outline the solution
3. Develop the outline into an algorithm
4. Test the algorithm for correctness
5. Code the algorithm into a specific programming language
6. Run the program on the computer
7. Document and maintain the program
Simple Program Design, Fourth Edition
Chapter 1
37
Summary
• Three different approaches to program design
were introduced, namely procedure-driven, eventdriven, and data-driven
• An algorithm was defined as a set of detailed,
unambiguous and ordered instructions
developed to describe the processes necessary
to produce the desired output from the given
input
• Pseudocode is an English-like way of
representing the algorithm
Simple Program Design, Fourth Edition
Chapter 1
38
Quick Quiz
1. A(n) _____________ lists the steps involved in
accomplishing a task.
•
ANSWER: algorithm
Simple Program Design, Fourth Edition
Chapter 1
39
Quick Quiz
2. ___________ is structured English that has been
formalized and abbreviated to look like high-level
computer languages.
•
ANSWER: Pseudocode
Simple Program Design, Fourth Edition
Chapter 1
40
Quick Quiz
3. A(n) __________ is the name given to a
collection of memory cells, designed to store a
particular data item.
•
ANSWER: variable
Simple Program Design, Fourth Edition
Chapter 1
41
Quick Quiz
4. Name three of the most common elementary
data types.
•
ANSWER: Integer, Real, Character, and Boolean
Simple Program Design, Fourth Edition
Chapter 1
42
Quick Quiz
5. ___________ files may be opened to read or to
write, but not both operations on the same file.
•
ANSWER: Sequential
Simple Program Design, Fourth Edition
Chapter 1
43