Chapter 2: Developing a Program
Chapter 2
Developing a Program
Prelude
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Concepts and Design
1
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Chapter 2: Developing a Program
2.1 The Program Development Cycle
• Problem solving principles
• Writing a program
– Completely understand the
problem
– Devise a plan to solve it
– Carry out the plan
– Review the results
Prelude
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Concepts and Design
– 1) Analyze the problem
– 2) Design the program
– 3) Code the program
– 4) Test the program
2
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Chapter 2: Developing a Program
1) Analyze the Problem
• Brewster’s Thousands
– The problem: Brewster wants to invest money at a
local bank. There are many options such as interest
rates, terms of deposit, compounding frequencies. He
needs a program to compute, for any given initial
investment, the final maturity (value) of the deposit.
• What are the inputs? (given data)
• What are the outputs? (required data)
• How will we calculate the required outputs from the given
inputs?
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Chapter 2: Developing a Program
2) Design the Program
Create an outline of the program
• An algorithm – a step by step procedure that will
provide the required results from the given inputs.
– Algorithms in real life: Instructions on how to make a
cake, use the bank’s ATM, etc.
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Chapter 2: Developing a Program
3) Coding the Program
• Once the design is completed, write the program
code.
• Code is written in some programming language
such as BASIC, Pascal, C++, Java, etc.
• In Vendit, we write code in pseudo-code,
developing the skills to be used when studying the
specific languages.
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Chapter 2: Developing a Program
4) Testing the program
• Locate any errors (bugs)
• Testing is done throughout the development cycle
• Desk-checking, or code walkthrough is
performed to locate errors in the code.
– Pretend you are the computer and execute your own
code.
• Ultimate test is to run the program to see if the
outputs are correct for the given inputs.
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Chapter 2: Developing a Program
2.2 Program Design
• Modular programming
– Determine the major tasks that the program must
accomplish. Each of these tasks will be a module.
– Some modules will be complex themselves, and they
will be broken into submodules, and those submodules
may also be broken into even smaller modules.
– This is called top-down design
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Chapter 2: Developing a Program
The first illustration of top down design describes the 3 fundamental
tasks that are required in the Brewster example:
– Input
– Perform Calculations (Process)
– Output
Input
Input variables:
Principal
PercentageRate
Term
Frequency
Perform Calculations
Output
Compute Rate of interest
Display
Set Rate = PercentageRate / 100
FinalValue
Compute final value of investment
Set FinalValue = Principal *
(1 + Rate / Frequency) ^ (Frequency * Term)
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Chapter 2: Developing a Program
A Code Module
• Performs a single task
• Is self-contained and independent of other modules
• Relatively short – less than 1 page
•
•
•
•
Calling module
Called module
Transfer of control
Main is the controller of all sub-modules
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Chapter 2: Developing a Program
Example of Modules in Pseudocode
Main module
Display program title and brief description of program
Call Input Data Module
Call Perform Calculations module
Call Output Results Module
End Program
Input Data module
Prompt for Principal, PercentageRate, Term, Frequency
Input Principal, PercentageRate, Term, Frequency
End module
Perform Calculations module
Set Rate = PercentageRate / 100
Set FinalValue = Principal * (1 + Rate / Frequency) ^ (Frequency * Term)
End module
Output Results Module
Write Principal, PercentageRate, Term, Frequency
Write FinalValue
End module
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Chapter 2: Developing a Program
Hierarchy Chart
• Like an organization chart – shows position of
modules in the program.
• Depicts what modules exist and how they are
related.
• Large programs need a “map” for documentation.
• One page of code per module – keeps the program
manageable.
• We will have very small modules while getting
comfortable using these tools.
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Chapter 2: Developing a Program
Hierarch Chart for Brewster Example
Main
Module
Input
Data
Prelude
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Concepts and Design
Perform
Calculations
12
Output
Results
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Chapter 2: Developing a Program
2.3 Coding, Documenting, and Testing
• Coding
– done in a specific programming language. We will use
pseudocode.
– should only begin after a solid design exists.
• Documenting
– Code needs to contain documentation that describes to
the reader what the code is doing – called comments
– This kind of documentation is for the programmers to
read
– There is also User Documentation that is external to
the code and may take the form of a User’s Guide
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Chapter 2: Developing a Program
• Testing
– Create test data that will be used to check the program’s
correctness. For example, if the following test data is
used in the Brewster example, does the program generate
the expected results? (Determine the expected results
before the code is written.)
•
•
•
•
Principal = 1000
PercentageRate = 12
Frequency = 4
Term = 6
If a Desk check of the code gets the same answer as the
expected results then the code has been tested, and is
likely correct.
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Chapter 2: Developing a Program
Types of Errors
• Syntax – wrong grammar, i.e., breaking the rules
of how to write the language
– Forgetting punctuation, misspelling keyword
– The program will not run at all with syntax errors
• Logic - the program runs, but does not produce
the expected results.
– Using an incorrect formula, incorrect sequence of
statements, etc.
– These errors are detected during the desk-check, of the
program; an important part of the cycle.
Prelude
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Concepts and Design
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Chapter 2: Developing a Program
2.4 Structured Programming
• A method for designing and coding programs in a
systematic, organized manner.
• It combines the principles of top-down design,
modularity and the use of the three accepted
control structures of sequence, repetition and
selection.
• Sequence, repetition and selection can be
expressed in pseudocode, or with Flowcharts
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Chapter 2: Developing a Program
Flowcharts
• Another tool for programmers to design programs
– Describe the flow of a program module’s execution
with diagrams.
– (Completely different from hierarchy charts).
– Connected symbols are used to describe sequence,
repetition, and selection.
– Some prefer to use flow charting to learn how to
express algorithms, and others prefer to use
pseudocode.
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Chapter 2: Developing a Program
The Flowchart for Brewster’s Thousands
Start
Input Principal, Rate,
Term, Frequency
Compute
Final Value = Principal *
(1 + Rate/Frequency)
^ (Frequency * Term)
Output
FinalValue
Ref: p52 Venit
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End
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Chapter 2: Developing a Program
C++ Coding for Brewster’s Thousands
// C++ program - by M. Wojciechowski
#include <iostream>
#include <cmath>
using namespace std;
int main()
{
int PercentageRate, Term, Frequency;
float Rate, Principal, FinalValue;
// Input Datat
cout << “Enter the interest rate: “;
cin >> PercentageRate :
cout << “Enter the principal: “;
cin >> Principal :
cout << “Enter the Term: “;
cin >> Term :
// Problem Calculation
Rate = PercentageRate / 100;
FinalValue = Principal * pow(1 + Rate/Frequency , Frequency*Term);
// Output Data
cout << “Given the principal is “ << Principal << “ and interest rate is “ << Rate
<< “ and the term is “ << Term << “ and the interest is paid “ << Frequency
<< “ times per year.” << endl;
cout << “Final value is “ << FinalValue << endl;
return 0;
}
Prelude
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Concepts and Design
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Chapter 2: Developing a Program
Test Data
Output Data
Input Data
Principal
Percentage
Rate
Frequency Term
1000
12
4
Prelude
to Programming
Concepts and Design
Rate
Final
Value
6
20
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Chapter 2: Developing a Program
C++ Compiler
Hwk1.cpp
Program Editor
Preprocessor
C++ Compiler
Produce an object file
Hwk1.obj
link all the object file in order
to produce an executable
program
Linkage
Hwk1.exe
Executable Program
Prelude
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Concepts and Design
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Chapter 2: Developing a Program
Control Structures
• Sequence –in sequential order.
– The simplest of control structures – start at the
beginning and continue in sequential order.
• Repetition – repeat statements more than once
– Called a loop, it needs a stop condition, I.e, the
program will continue to loop until some condition is
met.
• Selection – selectively execute statements
– Called a branch, it requires a condition to determine
when to execute statements.
Prelude
to Programming
Concepts and Design
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