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1 Outline Program development cycle. Algorithms development and representation. Examples.
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Outline
Program development cycle.
Algorithms development and representation.
Examples.
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Program Development Cycle Program development cycle steps:
Problem definition.
Problem analysis (understanding).
Algorithm development: Ways for algorithm representation:
Human language
Pseudocode.
Flowcharts (also called UML activity diagram).
Coding.
Execution and testing.
Maintenance.
Recall that such cycle and all the techniques presented in this lecture are the same for any programming language you want to use not only for C++.
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Problem Definition
To understand the problem is half the solution.
Describe it by precise, up to the point statements that will make both analyzing and solving the problem easier and clearer.
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Problem Analysis
Determine the inputs, outputs, and the required operations.
Explore all possible solutions.
Pick the easiest, in terms of implementation cost (space, time) one.
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Algorithm Development
Algorithm is a procedure that determines the: Actions to be executed. Order in which these actions are to be executed (which is
called program control and in industry it is called work flow).
So, it is a plan for solving the given problem. You must validate the developed algorithm, i.e. make
sure that it solves the correct problem. You must verify the developed algorithm, i.e. make
sure that it produces correct results. You must check the feasibility (in terms of the needed
resources, ease of implementation, ease of understanding and debugging, its expected execution time, etc.) of the developed algorithm.
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Algorithm Representation – Human Language
Use your own language to represent the steps of the developed algorithm.
Example: adding two integers:
1. Prompt the user to enter two numbers.
2. Add them and store the result.
3. Display the sum to the user on the screen.
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Algorithm Representation – Pseudocode Artificial, informal language used to develop
algorithms. Kind of structured English for describing algorithms. Middle approach between human language and C++
code. It is convenient and user friendly. Not actually executed on computers Allows us to “think out” a program before writing the
code for it Usually easy to convert into a corresponding C++
program Consists only of executable statements, i.e. no
definitions or declarations.
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Pseudocode Notations I Input:
Input from keyboard: Get. Input from file or memory location: Read.
Output: Output to printer: Print. Output to file: Write. Output to screen: Display, Prompt (usually followed
by Get).
Values assignment: Initial values: Initialize, Set. Results of computation: =, .
Keeping variables for later use: Save, Store.
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Pseudocode Notations II Arithmetic computation:
Either use exact operators (+, *, /, -) or equivalent words of them (add, multiply, divide, subtract).
Computations: either use Compute or represent the actual operation mathematically. E.g. Compute average or avg = sum/count.
Control structures: Use the actual words as it is: If, If – then – Else,
While, do – While, For – to --, ...
Relational operators: Write them as words: greater then, less than or
equal, etc. Or you can use their symbols: >, <=, etc.
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Pseudocode Examples Adding two numbers:
1. Prompt user for number1 2. Get number1 3. Prompt user for number2 4. Get number2 5. Add number1 and number2 6. Set sum to the result 7. Display sum
Other examples (on board):
Deciding the grade (A-F) of a student.
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Algorithm Representation – Flowcharts
Represent the algorithms or computer programs execution steps graphically.
The American National Standards Institute (ANSI) published a standard for flowcharts that includes a definition of their symbols (see next slide).
Pseudocode is preferred over flowcharts since: More readable. Can be converted into C++ code easier.
Flow charts are very similar to the UML (Unified Modeling Language) activity diagram with some differences in the used symbols.
UML is an industry standard for modeling software systems.
We will study flowcharts not activity diagrams in this course.
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Flowcharts Symbols
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Flowchart Examples
Numbers addition example.
Start
End
Get number1
Get number2
sum = number1 + number2
Display sum
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Decision flow chart
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Looping flow chart
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Example III
Write a program that reads three numbers from a file. If the multiplication of these numbers is greater than or equal their sum then print “Winner” on the screen”, otherwise print “Loser” on the screen.
Solution:
On board.
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Class Average Algorithm
Problem: Calculate and report the grade-point average for a class
Discussion: The average grade equals the sum of all grades divided by the number of students
Output: Average grade
Input: Student grades
Processing: Find the sum of the grades; count the number of students; calculate average
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Flowchart
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Pseudocode
Program: Determine the average grade of a class
Initialize Counter and Sum to 0
Do While there are more grades
Get the next Grade
Add the Grade to the Sum
Add 1 to the Counter
Loop
Compute Average = Sum/Counter
Display Average
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Coding
Writing the source code of your solution that is to convert the developed algorithm into code statements of the used language, i.e. C++.
Some useful tips: Make sure of using correct syntax.
Use meaningful identifiers to make your code more readable.
Add suitable documentation and comments.
Make your code modular or structured as possible.
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Execution and Testing
Compilation and debugging. Types of errors:
Syntax errors (Compile time errors): Errors caught by compiler
Logical errors (Runtime errors): Errors which have their effect at execution time
Non-fatal logic errors program runs, but has incorrect output
Fatal logic errors program exits prematurely
Tracing to verify your program with different sets of inputs.
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Maintenance
Not always applicable in education, i.e. highly required in real world jobs.
Update your code based on:
Discovered and reported bugs.
Customer feedback to make your application more efficient and flexible.
Upgrade the code.
