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Basic of C++

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Lecture Overview

Introduction to C++ Basic components of C++

Control Statements

Declarations

Functions

Useful Library in C

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What is C++?

A programming language developed by BjarneStroustrup

Originally known as C with Classes

Renamed to C++ in 1983

First commercial release in 1985 Main features:

General purpose

Object Oriented

Compatibility with C

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The Good and Bad News

Good News:

Only minor incompatibility with C

Most programs in C are valid in C++ withoutmodification

Proficiency in C++ is a great advantage: Much sought after in the industry

Picking up other OO languages like Java, C# isrelatively easy

Bad News: Compatibility with C detracts from pure Object

Oriented approach

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Advice

C++ is only a means used in learning datastructures and algorithms C++ coverage is done within 3-4 lectures!

Focus more on concepts and Ideas that are trueregardless of the actual implementation language

However, a heavy weight of your CA comes fromyour C++ proficiency: Labs

Programming questions in the midterm test and the final

exam

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Hello World! in C and C++

#include

using namespace std;

int main () {

cout

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Another simple C++ program#include

using namespace std;

const double PI = 3.14159;

int main () {

int radius;

cout > radius;

double area = PI * radius * radius;

double circumference = 2 * PI * radius;cout

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Control Statements

Program Execution Flow

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Selection Statements - 1 if-else statement

Valid comparison: boolean expression

Primitive values (0 = false, nonzero = true)

if (a > b) {

...

} else {

...

}

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// L01p3.cpp

#include using namespace std;int main () {

int i = -1;double d = 2.0;if ( d > i ) cout

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Simple Data Types

Integer data

Unsigned version can store only non-negative values

Character data

Unsigned version can store only non-

negative values

Floating point data

int

unsignedint

Constant modifier

As prefix of data types

E.g. const int i = 123;

Variable must be initialized when declaredand cannot be changed afterwards

const

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char

unsignedchar

float

double

[new]

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Simple Data Types [new]

Boolean data

Can have the value true or false only

Internally, true = 1, false = 0

Can be used in a condition

Improve readability

bool

bool done = false;

while (!done) {

if (...)

done = true;

}

Condition met, Im done

While not done

Example Usage

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// L01p5.cpp#include using namespace std;int main () {

bool done = false;int i = 1;while (!done) {

cout

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Enumeration [new]Color myColor;

...

switch (myColor) {case Red:

...

case Yellow:

...

case Green:

...}

int myInt;

myInt = myColor;

Color newColor;

newColor = Color(1);

enumcan be used in a switchstatement

enumcan be converted to integerBy default, 1st value == 0, 2nd value == 1 etc.i.e. Red = 0, Yellow = 1,

Similarly, integer can be converted toenumtype

newColor will have the value Yellowin this case

19Can you define bool as an enumeration?

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ArrayAn array is a collection of homogeneous data (data of

the same type)To declare an array of 10 integers:

int iA[10];

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// L01p6.cpp

#include using namespace std;int main () {

int iA[10];iA[0] = 123;iA[9] = 456;

iA[11] = iA[0] + iA[9];cout

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sizeof( )

Use sizeof( ) to find the number of bytes taken by a

variable (data type).

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// L01p7.cpp#include using namespace std;enum Color {

Red, Yellow, Green};int main () {

int iA[] = {3,1,5,6,9,3,5,7,3,8,9,4,5,3,2,8,0};cout

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How are variables allocated?

// L01p8.cpp

#include using namespace std;

int main () {

int i,j;

char a,b,c,d;

int m;

char e;

int n;

cout

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Array

Limitation:

A function return type cannot be an array

An array parameter is passed by address

An array cannot be the target of an assignment

int[10] someFunction( ) {...}

int ia[10], ib[10];// Initialize array ib

ia = ib;

Error: cannot return array

Error: array assignment isinvalid

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Structure A collection of heterogeneous data

Data can be of different type Data describe a common entity

Declaring the structure called

Person to store informationabout a person:

name: maximum 50 characters

age: integer

gender: m = male; f = female

s1 is a Person variable

struct Person {

char name[50];int age;

char gender;

};

Person s1;

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Structure Example Usage

Person s1 = { Potter, 13, m };

Person s2;

s2 = s1;

s1.age = 14;

s2.gender = f;

s2.age = s1.age * 2;

Declare & Initialize

Structure assignment. Everything copied.

Use . to access a field

Declare only

Read and store a field

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Size of a structure// L01p9.cpp

#include

using namespace std;

struct Person {

char name[50];

int age;

char gender;};

int main () {

Person s1 = { "Potter", 13, 'm' };

Person s2;

cout

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Pointer

A pointer contains the addressof a memory location

111

1024

1024

x

addressname content

ptr

int x = 111;

int *ptr;

ptr = &x;

*ptr = 123;

Declareptr as an int pointer

ptr points to x

Dereferenceptr

Note the different meanings of *

Declaring a pointer

Deference a pointer

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123

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{

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Pointer and Structure

Pointer can point to a structure

int main()

{

Person s =

{ "Potter", 13, 'm' };

Person *p; //Person Pointer

p = &s;

p->age = 14;

(*p).age = 14;

}

EquivalentStatements

'P'

13

1024

1074

'm ' 1078

1024

sage

name

gender

p

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struct Person {

char name[50];

int age;

char gender;

};

Person s1;

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Dynamic Memory Allocation : new [new]

Up to now, pointers are used to point to existing

(declared) variable Actually, new memory box can be allocated at runtime

Using the new keyword

Syntax:

new datatypewhere datatypecan be

Predefined data type: int, float, array

User defined data type: structure or class

Address of the start of the newly allocated memoryboxes is then returned

Usually we use a pointer variable to store the address

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new : Array of elements

Whole array can be allocated dynamically The size can be supplied at run time

intmain()

{

int size;

int *ia;

cout > size;

ia = new int[size];

ia[0] = ...

ia[1] = ...

}

ia

Assume size = 5

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delete : An example/* PERSON: a structure definedbefore*/

intmain(){

Person *p;

p = new Person;

p->age = 14;

delete p;

p = NULL;

p->age = 14;

}

p

Good Practice: Always set a

pointer to NULL after delete

Error!

Freememory

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NULL

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General Advices on using Pointers

Incorrect / Careless use of pointers can make your

life miserable: Program Crashes (Runtime Error):

Segmentation Fault / Bus Error

"Weird" behavior:

Program works erratically

Useful Guidelines: Always initialize a pointer

Set to NULL When:

Declaring a new pointer

After memory deallocation

Make sure a pointer is pointing to the right place!

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Reference [new]

A reference is an alias

(alternative name) for a variable

x

name content

intRef 456

int x = 456;

int& intRef = x;

// type of intRef is intintRef++;

cout

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Function

Modular Programming

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Function A function is a group of statements within a named block marked by { }

SyntaxReturn-type function-name(parameters) {

// body

}

only relies on parameters for input

output is well defined When the block is replaced by ;, we have the corresponding function

prototype

int factorial(int n)

{

int result = 1, i;for (i = 2; i

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Function Prototype and Implementation

int factorial( int );

int main( )

{

cout

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Function Overloading [new]int maximum(int a, int b) //Ver.1

{

if (a > b) return a;

else return b;

}

int maximum (int a, int b, int c) //Ver.2

{return max( max(a, b), c);

}

float maximum(float a, float b) //Ver.3

{if (a > b) return a;

else return b;

}

3 versions ofmaximum() function.

Note the difference in number and data type of parameters

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Function Overloading [new]

Whenever an overloaded function is called, the

compiler chooses the closest match1. Exact match

2. Safe promotion, e.g. char int, float double

3. Unsafe conversion, e.g. double float

maximum(1, 2, 3);

maximum(a, b);

double f1, f2;

maximum(f1, f2);

Version 2 called

Version 1 called

Version 3 called

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f A

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Function : Default Argument [new]

In C++, function parameter can be given a default value

Default value is used if the caller does not supply anactual argument

double logarithm( double N, double base = 10 )

{ ... Calculates Logbase(N) ... }

int main( )

{

cout

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Function : Default Argument [new]

Parameters with default values should appear last in

the parameter list E.g. f(int i, int j = 123, int k = 456)

But not f(int i, int j = 123, int k)

Similarly, when using a function with defaultparameters

Only trailing arguments can be omitted

E.g. Given

f(int i, int j = 123, int k = 456)

f(999); //ok. Equal to f(999, 123, 456)

f(999, 888); //ok. Equal to f(999, 888, 456)

f(999, , 777); //compilation error

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F i P b dd / i

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Function : Pass by address/pointer

void swap_ByAdr( int* a, int* b )

{ int temp;

temp = *a;

*a = *b;

*b = temp;

}

123

456

1024

1028

1024

1028

i

j

a

b

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int main()

{ int i = 123, j = 456;

swap_ByAdr(&i, &j);

cout

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F i A P i S

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Function : Argument Passing Summary

By Value: Simple data types (int, float, char etc) and simple

structures are passed by value (copying the arguments)

Cannot change the actual argument

By Address:

Requires the caller to pass in the addresses of variablesusing &

Requires dereferencing of parameters in the function

Arrays are passed by address

By Reference: No additional syntax required except to declare the

parameters as reference variables

No copying of arguments

Faster execution and less memory usage

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Useful Library

Cant live without them

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