Introducing C++ Elements

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Outline

Main algorithms’ constructs General form of a C++ program {section

2.5} C++ language elements {section 2.1} Executable statements {section 2.4} Reserved words and symbols {section

2.2} Data types {section 2.3}

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Main Algorithms’ Constucts An algorithm is written as a step-by-step

procedure (sequence) in which choices can be made where necessary (selection), and all or part of the algorithm can be repeated (repetition).

Thus, the basic control structures of algorithms are:1- Sequence2- Selection 3- Repetition

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SequenceAn algorithm is based on the

notion of sequence, which is the ordering of steps/statements.

Step n cannot be started until step n-1 is complete.

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General Form of a C++ Program// File: filename// Program description: ….

#include directivesusing namespace std;

void main(){

Variables declaration section

Executable statements section}

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General Form of a C++ Program (cont’d)

Function (a collection of related statements) is the basic unit in C++

A C++ program must contain a main function

void main ()void - function returns no valuemain - lower case followed by (){ } - braces define the function body

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General Form of a C++ Program (cont’d)

General form of function body partsDeclaration statements

Variables and constantsExecutable statements

C++ statements

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Comments Comments make a program easier to

understand They are ignored (i.e. not translated) by the

compiler // used to signify a comment on a single line /* Text text */ used for comments on

multiple lines

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Compiler Directives #include

Compiler directiveProcessed during compilation process Instructs on what you want in the program

#include <iostream>Adds library class/file called iostream to

programUsed with < >Also “ “ user defined

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Program Processing Diagram

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Program Processing Diagram (2)

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<iostream>Included in iostream

cout refers to the standard output device; i.e. the screen

cout << "Hello!"; << output operator

(insertion operator) cin refers to the standard input

device; i.e. the keyboardcin >> N1 >> N2;

>> input operator (extraction operator) directs input to variable

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Executable Statements

cout displays output on the screencout << “Enter the distance in miles: ”;

cin gets input from the keyboardcin >> miles;

Assignmentkms = KM_PER_MILES * miles;

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Reserved Words and Symbols Reserved words have special meanings

Can NOT be used for other purposes (const, float and void are some examples)

Special symbols / delimitersC++ has rules for special symbols

= * ; { } ( ) // << >> [ ] , + -

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Data Types Predefined data types

int (integer)Positive or negative whole number1000 12 199 100000The size of an int depends on the machine and the

compiler. On a PC it is usually a word (16 bits).Other integers types are:

• short: uses less bits (usually a byte)• long: typically uses more bits (usually 2 words)

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Data Types (cont’d) float (floating point / real number)

Positive or negative decimal number 10.5 1.2 100.02 99.88 Integer part and fraction part The number 108.1517 breaks down into the following

parts• 108 - integer part• 1517 - fractional part

Other floating-point data types are:• double• long double

bool (boolean) true false

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Data Types (cont’d)

char (character)Represents a characterIndividual character value (letter or

number)Character literal enclosed in single quotes

‘A’Characters are encoded using a scheme

where an integer represents a particular character

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Exercise

ProblemAnalyse, design (using a flow chart), and implement (using C++) an algorithm that calculates, and outputs the sum (sum) of three numbers (n1, n2 & n3) input by the user.

Analysis Input

float n1: first variablefloat n2: second variablefloat n3: third variable

Outputfloat sum: sum of n1, n2, & n3

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Exercise (cont’d)

INPUTn1, n2, n3

OUTPUTsum

START

STOP

sum = n1 + n2 + n3

Design

Implementation (C++)#include <iostream>using namespace std;void main ()

{float n1, n2, n3, sum;

cout << “Please input three numbers”;cin >> n1 >> n2 >> n3;

sum = n1 + n2 +n3;

cout << “The sum is” << sum;

}

Proc

essin

g

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Addition.cpp/* FILE: Addition.cpp PROGRAM: Adds three numbers input by the user */

#include <iostream>using namespace std;

void main (){ float n1, n2, n3, sum; // declaring variables

cout << “Please input three numbers”; cin >> n1 >> n2 >> n3; // inputting 3 variables sum = n1 + n2 + n3; // adding the 3 variables

cout << “The sum is:” << sum; // outputting sum}

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Next lecture will be about

Arithmetic Expressions