C++ Basics - IPN Orsayipn€¦ · · 2018-01-04I. Hrivnacova @ Data Processing Course 2018 2 C++ Programming language Features: – C++ is C. C++ supports (almost) all the features

I. Hrivnacova @ Data Processing Course 2018 1

C++ Basics

Data Processing Course,I. Hrivnacova, IPN Orsay

● The First Program

● Comments

● Function main()

● Input and Output

● Namespaces

● Variables

● Fundamental Types

● Operators

● Control constructs


C++

● Programming language

● Features:– C++ is C. C++ supports (almost) all the features of C. Like C, C++ allows

programmers to manage the memory directly, so as to develop efficient programs.

– C++ is OO. C++ enhances the procedural-oriented C language with the object-oriented extension. The OO extension facilitates design, reuse and maintenancefor complex software.

– Template C++. C++ introduces generic programming, via the so-called template.You can apply the same algorithm to different data types.

– STL. C++ provides a huge set of reusable standard libraries, in particular, theStandard Template Library (STL).


C++ Standards

● C++ is standardized as ISO/IEC 14882. Currently, there are twoversions:– C++98 (ISO/IEC 14882:1998): 1st standard version of C++.

● C++03 (ISO/IEC 14882:2003): minor "bug-fix" to C++98 with no change tothe language. Commonly refer to as C++98/C++03 or First C++ standard.

– C++11 (ISO/IEC 14882:2011): 2nd standard version of C++. Formerlycalled C++0x, as it was expected to finalize in 200x. It adds somenew features to the language; more significantly, it greatly extendsthe C++ standard library and standard template library (STL).

● We will use some features introduced in C++11 in our course, too


C++ Program

/* The first C++ program * - just outputs 'Hello, World !' */

#include <iostream>

int main() { // print “Hello, World !” on the screen std::cout << “Hello, World !” << std::endl; }


C++ Program


#include <iostream>


Comments: ● /* */ - can span over several lines or be inserted in the code on one line● // - lasts to the end of the line


C++ Program

Include statement(s): ● Including all necessary declarations for input and output


#include <iostream>



C++ Program

The main function● called at the program startup, leaving main() ends the program


#include <iostream>



C++ Program

A statement ending with a semicolon;● It writes the string “Hello, World !” followed by std::endl symbol,

to the standard output


#include <iostream>



Function main()

● The function main is called at the program startup, leaving main() ends the program

● The function head:– int the return type

– main the function name

– () the parameter list

● The function main() returns integer value– If return statement is not present, the zero value is returned implicitly

– You can also write the statement explicitly:

– return 0;

● In C programs the return statement cannot be omitted


Input and Output (IO)

● C/C++ IO are based on streams,which are sequence of bytesflowing in and out of the programs(just like water and oil flowingthrough a pipe).– In input operations, data bytes flow

from an input source (such askeyboard, file, network or anotherprogram) into the program.

– In output operations, data bytesflow from the program to an outputsink (such as console, file, networkor another program).

Chua Hock-Chuan: Programming Notes


Input and Output

● The input/output (I/O) functionality isprovided in components of standardlibrary

● To get these components known tothe program:– #include <iostream>

● Standard channels to provideinput/output:– Generally assigned to the keyboard

(input) and the screen (output)

– Can be redirected by the operatingsystem to a file

● Symbols– std::cin - input channel (the

keyboard)

– std::cout - output channel (thescreen)

– std::endl - line break (new line)

● << operator :– Send data to the output channel

● >> operator :– Read data from an input channel


Namespaces

● The prefix std:: is used for all symbols of the standardlibrary

● Using the namespace concept, symbols can be groupedlogically within a package (or a component)

● Avoids names clashes in large program

● using namespace directive can be used to make all symbolsfrom a namespace available without std:: prefix

#include <iostream>

using namespace std;

cout << “Hello, World !” << std;


“Four digits” program

● We will discuss the “Four digits” program (from the C++ book)line by line to learn the basic language concepts:– Variables, Types, Operators and Control Constructs

● The program will list all four digits numbers that fulfill thefollowing condition

● If you split a four digits number into two parts each having twodigits and add the squares of these numbers, you get theoriginal four digit number:– Eg. 1233 = 12*12 + 33*33


Code#include <iostream> // C++ header file for I/O


int main() { int counter = 0; // current number of found four-digit numbers

// for every number from 1000 to 9999 for (int number=1000; number<10000; ++number) {

// separate the first and last two digits int front = number / 100; // the first two digits int back = number % 100; // the last two digits

// if the sum of the squares produce the original number, // output number and increment counter if (front*front + back*back == number) { cout << number << " == " << front << "*" << front << " + " << back << "*" << back << endl; ++counter; } }

// output number of four-digit numbers found cout << counter << " numbers found" << endl;}


Variables #include <iostream> // C++ header file for I/O







A variable counter is defined to counthow many four-digitnumbers were found:● int ~ type● counter ~ name● = 0 ~ initialized to

the value 0


Variable

● It allocates memory● The current memory content

is its value ● counter has the value 0● The size of memory

allocated and the operationswe can do with a variableare defined by its type

counter 0 int

NAME VALUE TYPE

number 1556 int

pi 3.141592 double

A variable has a name, stores a value of the declared type


Variable Declaration

● Variable declaration = the instruction that creates the variable

● We can declare a variable without giving it an initial value; its value is undefined

int counter;

● We can also declare a variable with giving it its initial value:

int counter = 0;

● Other ways of initialization:

int counter(0);

int counter = { 0 };

● We prefer to declare variables just before their use

● The const declaration of a variable - creates a variable that can not be changed later

const double PI = 3.14;

PI = 5.4; // error: cannot assign to variable 'PI'

// with const-qualified type 'const double'


Variable Type

● Defines how the object (its binary configuration in memory) can be manipulated

● Fundamental types– Numeric: integer (int), floating point numbers (float, double)

– Characters: char● Enclosed in single quotes: 'a', '0'● Special characters must be masked with a backslash: \', \”

– Boolean: bool: can have only two values: true, false

● Object types– Defined in the C++ standard library and by the programmer

● Have their own defined functions; can also have their own defined operators

● enum: for enumeration types (names that represent integral value)

● void: “nothing” (for functions without a return value)


Loop#include <iostream> // C++ header file for I/O







For loop:● iterates over certain

values● composed of 3

statements:1)int number=1000;

2)number<10000;

3)++number

1) Initialize loop variable:executed once

2) Condition: loopcontinues as long asthe condition is true

3) Increment loopvariable: in eachiteration


Loops

for (int i = 10; i < 10; ++i ) { ...}

int counter = 10;while ( counter < 10 ) { ...}

int counter = 10;do { ...} while ( counter < 10 );

● “For” loop

● “While” loop = pre-test loop

– preferred when it is possible thatthe block of code will not beexecuted

● “Do” loop = post-test loop

– preferred when the block mustalways be executed (at leastonce)


Loops: break, continue

● break - allows to quit theloop earlier

● continue - allows to skipone iteration

● But be careful - it should notbe abused (sign of “bad”programming style)

for ( int i = 0; i < 10; i++ ) { if ( i == j ) continue; if ( i > k ) break; // do something }


Operators#include <iostream> // C++ header file for I/O







Using operators toseparate first two andlast two digits:● Operator '/'

~ division● Operator '%'

~ modulo


Operators

Basic operators

+ addition, positive sign - subtraction, negative sign * multiplication / division % modulo operator

< less than <= less than or equal to > greater than >= greater than or equal to == equal to != not equal to

Basic operators

&& logical AND|| logical OR! logical negation

Assignment Operators:

= simple assignment+= addition-= subtraction*= multiplication/= division ...

Increment andDecrement Operators

a++ postfix incrementa-- postfix decrement++a prefix increment--a prefix decrement

Bit operators

Special operators


Tests#include <iostream> // C++ header file for I/O







An if statement checks whether thesum of the squares oftwo-digits numbersproduces the originalnumber● Inside if using

multiplication (*),addition (+) andequal to (==) operators

● Note == is differentfrom =


Tests

if ( x < 7 ) { cout << “x is less than 7” << endl; }

if ( x < 7 ) { cout << “x is less than 7” << endl; } else { cout << “x is greater than or equal to 7” << endl;}

● The {} are not necessary if the expression does not exceed one line● But we prefer to include always braces in order to avoid a possible problems

when extending the code on more lines


Flow Control

Chua Hock-Chuan: Programming Notes









If the condition insideloop is satisfied:● An appropriate

message is writtento the standardoutput channel:

1233 == 12*12 +33*33

● The counter isincreased by oneusing incrementoperator:

++counter









The result (the valueof all numbers found) isthen printed at the endof program: X numbers found

Documents

C++ Basics - IPN Orsayipn€¦ · · 2018-01-04I. Hrivnacova @ Data Processing Course 2018 2 C++ Programming language Features: – C++ is C. C++ supports (almost) all the features