CPlus Pres 1

8/12/2019 CPlus Pres 1

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What is C++ ?

C++ is a Object oriented programminglanguage. Initially named as C with

classes.

C++ was developed at AT & T BellLabs.

C++ is superset of C.Three important facilities are added

onto C.

Classes

Functions overloadingOperator overloading

C++ also allows us to create hierarchyrelated objects.

All C programs are also C++ programswith few differences.


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Input / Output

# include OR# include

using namespace std

std: standard input/output

iostream.h contains declaration forinput/output statements.

(Naming conventions of header files may

vary such as iostream.hpp

cinand cout are predefined objectsin for single interface.

cin >> number is an input statement& causes program to wait for user to

type in a number.

The identifier cin is a predefined object in C++ that corresponds to the standard

input stream (keyboard).


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Operator >> is known as extraction orget from operator that extracts or getsvalue from keyboard.

This corresponds to scanf( ) .The statement cout


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Cascading of I/O operators

In the statement cin >> num1 >> num2the values are assigned from left to right

cout


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Structure of C++ program

Include files

Class declaration

Class functions definitions Main function program


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Data types of C++

C++ Data Types

User_ defined Built_in Derived type

structure int array

union char function

class float pointer

enumerated double

void


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Void

(Available in C & C++ both)

Specifies the return type of a function thatdoes not return any value.

Indicates empty argument list in a Function.Use of void in declaring generic pointers in

C++.

void *p ;

int *i ;p = i ;

// assigns ipointer to void pointer p

i = p ; // not allowed

So p can be assigned a pointer value ofany basic data types.

void pointer may not be dereferenced.


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User Defined DT

struct and unionare same as in C

enumeratedDT slightly differ in C++enum shape {circle, square, triangle};

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here shape becomes new typename and can be used to declare

new variables.

shape ellipse;

enum color {red, blue=4, green=8}

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enumcolor {red=5, blues=6, green=7}

enum{off, on} {without name}

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int switch1 = off;

int switch2 = on;


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Pointers

Available in C & C++

int * i;i = & x;

// address of x is assigned to i

*i = 50;

// 50 value assigned to a location// pointed out by i i.e. assigining

// value 50 to x through indirection.


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Variable declaration

In C, all variables are declared at thebeginning of the scope.

But in C++, declaration of a variable beanywhere in the scope but before the first use.

Advantage

It makes program easier to understand.Disadvantage

Cant see all variables at a glance used in thescope.

Additional feature of C++ is in dynamicinitialization i.e., it permits runtime

initialization.

float average = sum / i;


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Constants

C++ constants are to be initialized as:const int size =10;

char name[size];

enum { X, Y, Z};

const X = 0; const Y = 1;

const Z = 2;

enum { X=10, Y=20, Z=15};

const X = 10; const Y = 20;

const Z = 15;

Only integer constants can be definedusing enum data type.


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Reference variables

C++ introduces a new kind of variablecalled reference variable that provides

an aliasfor previously defined variable.

data type &ref_var = var_name

float total;

float &sum = total;

sum and total both are same locations.// a is initialized to new line constant

char &a = \n

Major application is in passingarguments to functions

Call by reference mechanism isprovided in C++ explicitly


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Scope resolution operator

{ :

int x = 10

{ int x =1;

x is of inner block

Scope resolution operator :: x = x +1;

};

} x is of outer block

Declaration in an inner block hides adeclaration of the same variable in an outer

block


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Memory management operators

Along with malloc() & calloc(), C++also defines two unary operators new

and delete. These operators operate on

the free store of memory (also called

free storeoperators).Life time of an object is directly under

our control & unrelated to a block

structure.

Object created with new will remainuntil destroyed using delete.

Including user defined

pointer_var = new data_type;

both of the same type

int *p;float *q; int *p = newint[2];

p = newint[2]; float *q = newfloat;

q = newfloat;


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Creates memory space for an array of 2integers where p[0] refers to first element.

delete p;

delete q;

delete p[ ] specify size

In case of insufficient memory, newreturnsnull pointer.

Advantages over malloc ( )

Automatically computes the size ofdata object.

Possible to initialize object whilecreating memory space. These can be overloaded.


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Functions in C++

The function intmain ( )returns avalue of type int to the operatingsystem.

(optional as it takes by default)

If intbefore main ( ) is specifiedthen return statement for terminationbe used.

Normal convention is that if value 0is returned then the program ransuccessfully while non zero value

means some problem.


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Function prototyping is must in C++which gives compiler details as numberand type of arguments and return type.

float volume (int, float, float);

Should precede function definitionNo need to specify arguments.In C++, function without arguments canbe written as

void display ( );

Or

void display (void);

However in C, ( ) means any number ofarguments .In C++, this can be written openparameter list as voiddo-something ()


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Call by reference

In C++, parameters can be passed as referenceor value but in C it is passed by value only.void swap (int &a, int &b)

{ int t =a; int t; t = a;

a = b;

b = t; In C++}

Call - swap(m,n)

void swap (int *a, int *b)

{ int t;t = *a;

*a = *b; In C*b = t; }

Call swap(&m,&n)

Each argument in function must be declaredIndependently inside the parentheses.


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Return by reference

A function can also return a referenceint &max (int &x, int &y);

{ if (x > y) return x;

else return y;

}

Call max (a, b) returns a reference toeither a or bdepending upon whether value

of a or b is returned.

This implies that function call can appearon L.H.S in contrast to other programming

Languages (including C).

max ( a, b ) = -1

assigns a = -1 if a > b

b = -1, otherwise


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Default Arguments

C++ allows to call a function withoutspecifying all its arguments.

In such cases default values are specifiedwhen function is declared.

Default values are always specified fromright to left.

float amount (float p, int t = 3, float r = 0.15);

Various Calls:

value = amount (5000, 7, .12);

value = amount (5000, 7)here value of r=0.15 is taken

value = amount (5000)here t = 3 and r = 0 .15


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Function Overloading

Same function name can be used to createvariety of tasks .

It is called function polymorphismin OOP.// declarations

int add (int, int);

int add (int, int, int);

double add (double, double);

double add (int, double);double add (double, int);

// Calls

x = add(5,10);

x = add(5,10,15);x = add(2.5,10.2);

x = add(5,10.9);

x = add(5.5,10);


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Compiler tries to find exact match wheretypes of actual arguments match.

If exact match is not found then it performsinternal conversions.

float long

int float

float int etc.

For multiple matches error message isgenerated.

long sq (long x);

double sq (double x);

sq (10)

long double error message

To avoid such situation sq( ) should be used.


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Inline function

Ordinary function are compiled separatelyand are called as and when required.

In order to save time/overheads in callingfunction & returning to called program, apowerful facility is available in C++ .

Inline function is defined such asinline int sq (int x )

{return (x *x) }

call to inline

function is same

p = sq (2); q = sq (3);

Inline function are not called at executiontime instead function call is expanded by

the body of function.


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Inline modifier lets compiler mark aparticular function to be expended

rather than compiled.

C++ compiler may ignore your requestif your function is too long.

Advantage of inline function is thatit can help you to write well designed,modular programs that remain efficient

at the code level.

const rate = 1.5

inline float tax (x)

{

y = tax(p + 2); return (x * rate )

};

Speed benefits of inline functions will goif the size of function grows.


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In C, similar effect is achieved by macrodefinition defined by primitive # define.

Here macro preprocessor performs textualsubstitution.

# define rate 1.5

# define tax (x) x * rates

Macro call tax (p + 2) is expanded asp + 2 * rate which is not theintention.

Macros cant have local variables and itdoes not even define a block. Macros also do not permit parameter

checking.

C++ solves the drawbacks of C macrowith inline function which is small

function of one or two lines.


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Some situations where inline expansionmay not work.

Functions returning values, ifa loop, a switchor a goto

exist.

Functions not returning valuesif a return statement exists.

If functions contain staticvariables.

If functions are recursive.

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