C++ lecture 2

 You must verify the developed algorithm, i.e.. Algorithm Representation – Human Language Use your own language to represent the steps of the developed algorithm.. The Hashemite Univ

 Program development cycle.

 Algorithms development and

representation.

 Examples.

 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

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.

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.

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

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

Pseudocode Notations I

 Input from keyboard: Get

 Input from file or memory location: Read

 Output to printer: Print

 Output to file: Write

 Output to screen: Display, Prompt (usually

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.

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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 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

Flowcharts Symbols

Flowchart Examples

 Numbers

addition

example.

Decision flow chart

Looping flow chart

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.

Class Average Algorithm

grade-point average for a class

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

Flowchart

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

 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.

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.

 Not always applicable in education, i.e highly required in real world jobs.

 Update your code based on:

application more efficient and flexible.

Additional Notes

 This lecture covers the following

material from the textbook:

 Chapter 2: Sections 2.1 - 2.3