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Basic of C++

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Online References C++ Online Reference

http://www.cplusplus.com/reference/ http://www.cppreference.com/wiki/

SGI STL Programmers Guide

http://www.sgi.com/tech/stl/

C++ Quick Reference Sheet http://www.sourcepole.ch/sources/programming/cpp/c

ppqref.html

Bjarne Stroustrup

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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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Hello World!

#include

using namespace std;

int main () {

cout

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#include directive

The #include directive has two forms:

For standard library headers, use

#include

For user-defined header files, use

#include "file-name"

The user-defined header files will end with.h.

The standard library headers do not end with .h.

headers that starts with c are obtained from C library

E.g., , , ,

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Input and Output

Output using cout

Input using cin

To use either cin or cout, use the following two lines at

the start of program

#include using namespace std;

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The using Statement

A Namespace allows us to group classes, objects and

functions under a given name. The C++ standard library put all classes, objects and

functions within the namespace std. The line

using namespace std;tells the compiler to make available all names in thenamespace called std.

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A Simple C++ Program// L01p02.cpp

#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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Notation used in C++ lecture notes

Topics covered in the introduction are tagged with:

[new] topics introduced in C++, not valid in C

[expanded] topics covered in C, but greatly expandedin depth in C++

Topics without tags are revision on basic language

constructs valid in both C and C++

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Control Statements

Program Execution Flow

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Selection Statements - 1 i f - el se statement

Valid comparison: boolean expression

Primitive values (0 = false, nonzero = true)

if (a > b) {

...

} else {

...

}

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// L01p03.cpp

#include using namespace std;int main () {

int i = -1; double d = 2.0;cout

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Selection Statements - 2

swi t ch- case statement

Variables in switch( ) must be integer

type (or can be converted to integer) br eak : jump out of the switch block

def aul t : catch all unmatched cases

Optional

switch (a) {

case 1:

...

break;

case 2:

case 3:

...

default:}

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// L01p04.cpp#include using namespace std;int main () {

cout score;

switch (score) {case 10:cout

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Repetition Statements

whi l e : check condition before

executing body

while (a > b) {

... //body

}

do {

... //body

} while (a > b);

A : initialization (e.g. i nt i = 0)

B : condition (e.g. i < 10)

C : update (e.g. ++i )

Any of the above can be empty

Execution order:

A, B, body, C, B, body, C

for (A; B; C) {... //body

}

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do- whi l e: check condition after

executing body

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Declaration

Simple and composite data types

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Primitive Data Types

Data Type (Intel x86)

short -32,768 through 32,787

unsigned short 0 through 65,535

int -2,147,483,648 through 2,147,483,647

unsigned int,size_t 0 through 4,294,967,295

long -2,147,483,648 through 2,147,483,647

unsigned long 0 through 4,294,967,295float Approximately10-38 to 1038 with 7 digits

of precision

double Approximately10-308 to 10308 with 15

digits of precision

long double Approximately10-4932 to 104932 with 18digits of precision

char The 7-bit ASCII characters

signed char -128 through 127

unsigned char 0 through 255

bool true or false15

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Variable Declaration

Form:

type-namevariable-name;type-namevariable-name = initial-value;

type-namevariable-name(argument-list);

type-name may be

A primitive type or

A user-defined (class) type.

Example

int i;

double x = 5.5;

double y(6.7);point p(x, y);

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Automatic Type Conversion

If the operands are of different types, thefollowing rules apply in this order:

If either operand is long double, convert the otherto long double.

If either operand is double, convert the other todouble.

If either operand is float, convert the other tofloat.

If either operand is long, convert the other to long. Convertchar and short to int

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Explicit Type Conversion

An expression of one primitive type can be

converted to another primitive type using theform:

new-type(expression)

Example

Ifi is an int and y a doublei = int(y);will convert y to an int and store it in i.

The statement:i = y;

will do the same conversion.

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Constant modifier

As prefix of data types

E.g. consti nt i = 123;

Constant must be initialized when declared andcannot be changed afterwards

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Character Constants

The form'c' The form'\x' called an escape sequence:\aalarm \\ backslash\b backspace \? question mark\f formfeed \' single quote

\nnewline \" double quote\r carrige return \ooooctal number\thorizontal tab \xhh hexadidecimal number\v vertical tab

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C-String Constants

The form"sequence of characters"

is called a C-string constant (or simply string constant).

Note escape sequences may appear in the sequence ofcharacters.

String constants are stored as arrays of charactersfollowed by a '\0'.

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bool [new]

Boolean data

Can have the value true or false only

Internally, true = 1, false = 0

Can be used in a condition

Improve readability

When an expression regarded asboolean data will be interpreted as trueif it is non-zero or false otherwise

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// L01p05.cpp#include using namespace std;

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

cout

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Enumeration

Enumeration allows the programmer to declare anew data type which takes specific values only

enumColor {

Red, Yellow, Green

};

Color is a new data type

Values that are valid for aColor variableExample Declaration

Color c1, c2;

c1 = Yellow;

c2 = c1;

Example Usage

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Use of enumeration makes program more readable.

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Enumeration in switchColor myCol or ;

/ / enumcan be used in a switch statement

swi t ch ( myCol or ) {case Red:

. . .case Yellow:

. . .case Green:

. . .}

/* Symbols defined in enumare given integer values:

By default, 1stsymbol == 0, 2ndsymbol == 1 etc.

i.e. Red = 0, Yellow = 1, Green = 2 */cout

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Operator PrecedenceRank Operator Operation Associativity

1 [] Array subscript Left() Function call. Member access-> Member access

++ -- Postfix increment or decrement

2 ++ -- Prefix increment or decrement*

Pointer de-referencing operator& Address of operator+ - Unary plus or minus! Complement~ Bitwise complement

new Object creation

3 * / % Multiply, divide, remainder

4 + - Addition, Subtraction

5 > Shift right

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The smaller rank, the higher precedence

(logical)

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Operator Precidence (2)Rank Operator Operation Associativity

6 < >= Greater than, Greater than or equal

7 == Equal to! Not equal to

8 & Bitwise and

9 ^ Exclusive or

10|

Bitwise or11 && Logical and

12 || Logical or

13 ?: Conditional

14 = Assignment Right*= /= &=

+= -= = &= |=

Compound Assignment

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!=

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Prefix and Postfix Increment

Prefix:

++x --x

Postfix

x++ x-

Assume that i has the value 3. Then

z = ++i;

would result in both z and i having the value 4.

Butz = i++;

would result in z having the value 3 and i the value 4.

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The Conditional Operator

Form:

boolean-expression?value1:value2

If the boolean-exression is true, then the result is value1otherwise it is value2.

Example:

s =(score > 10? "true" : "false" );

In most cases the same effect can be achieved using theif-else statement.

Example: The above conditional statement is equivalent toif (score > 10) {s = "true";}

else {s = " false";}

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ArrayAn array is a collection ofhomogeneous data (data of

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

int iA[10];

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// L01p06.cpp#include using namespace std;int main () {

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

iA[10] = iA[0] + iA[9];cout

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sizeof( )

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

variable (data type) during compilation.

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// L01p07.cpp#include using namespace std;

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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Array Cannot Be Used In

i nt [ 10] someFunct i on( ) {. . . }

i nt i a[ 10] , i b[ 10] ;/ / I ni t i al i ze ar r ay i b

i a = i b;

Error: cannot return array

Error: array assignment isinvalid

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Structure A collection of data that can be of difference types

Declaring the structure called Personto store information

about a persons name, age, and gender

s1 is a Personobject

structPerson {char name[50];

int age;

char gender;

};

Person s1;

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Use of a Structure

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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Pointer A pointer variable contains the

address of another variable A pointer variable takes up 4 bytes

111

1024

1024

x

addressname content

ptr

int x = 111;

int *ptr;

ptr = &x;

*ptr = 123;

Declare ptr as an int pointer

&: address-of operator

Dereference ptr

Note the different meanings of*

To declare a pointer

To deference a pointer

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123

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NULL pointer

A null pointer points to nowhere and it has the value

NULL. NULL is defined in as 0:

When a pointer is regarded as a boolean,

a null pointer is regarded as false, and

a non-null pointer is regarded as true.

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Pointer and const const is used to prevent modification of a variable

How does it work with pointers?

i nt i = 7;

const i nt *p = &i ;

/ / i nt const *p = &i ;

*p = 8;

i = 8;

i nt * const q = &i ;

q = p;

const i nt * const r = &i ;

*r = 8;

r = p;

p points to an integer constant

Are const int the same as int const?

Error: cannot change constant

qis a constant pointerto int

Error: cannot change constant pointer

r is a constant pointerto a constant integer

Error

Error

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Pointers and Arrays

Array name is a constant pointer

Points to the first element (with index 0)

1032

3

1024

1032

5 1036

7 1040

iaint ia[3] = {3, 5, 7};

int* ptr;

ptr = ia;

ptr[2] = 9;

ptr = &ia[1];

ptr[1] = 11;ia = ptr;

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ptr 1032

Error

9

1036

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Pointer Arithmetic [expanded]

Pointer +n and pointer -n are valid expressions

int ia[5] = {1, 22, 3, 4, 5};

int* p = ia;

int *q, *r;

q = p + 4; //what is q?

r = q 1; //what is r?

cout

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Pointer Arithmetic [expanded]

Two forms of element access for arrays: Using [ ], i.e. indexing

Using pointer arithmetic

int ia[5] = {1, 2, 3, 4, 5};

for (int i = 0; i < 5; i++)

cout

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Pointer and Structure

Pointer can point to a structure

int main()

{

Person s =

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

Person *q; //Person Pointer

q = &s;

(*q).age = 14;

q->age = 14;

}

EquivalentStatements

'P'

13

1024

1076

'm' 1080

1024

sage

name

gender

q

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struct Person {

char name[50];

int age;

char gender;

};

14

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Dynamic Memory Allocation : new [new]

Up to now, pointers are used to point to existing

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

runtime Using the newkeyword

Syntax:

newdatatype

where datatype can be

Predefined data type: int, float

User defined data type: enum, structure or class

Address of the start of the allocated memory is returnedby new and it is stored in a pointer variable

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new : Single Element

int main()

{

int x = 123;

int *p, *q;

p = &x;

q = new int;

}

x 123

1024

1024

addressname content

p

q

x

3000

1024

1024123

pq

3000

New Memory

Box

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Memory Leak

q is the only variable storing the address of the new memory boxat 3000

If q is changed, the address of the new memory box is gone andthe memory box cannot be accessed even though it is there. Thisis known as memory leak

int main()

{

int x = 123;int *p, *q;

p = &x;

q = new int;

q = p;

}

x

3000

1024

1024123

pq

3000

Memory

Leak!

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1024

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new : Array of elements

An 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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new : Structure

Dynamic allocation for structure can be done

similarly

intmain()

{

Person *p;

p = new Person;

p->age = 14;

}

At this point

p

age

name

gender

Memoryspacefor 52

chars

45

14

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Releasing memory to system : delete

Objects created using the new operator can only be

destroyed using the delete operator. Syntax:

deletepointer

delete [ ]pointer_to_array

Note: Delete is to deallocate the memory pointed by the

pointer. Delete is not used to deallocate the pointer

Dereferencing pointer after delete will produceunpredictable result!

Using delete instead of delete[] to deletean array will produce unpredictable result.

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A

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

intmain(){

Person *p;

p = new Person;

p->age = 14;

delete p;

p = NULL;

// many other statements

p->age = 15;

}

p

Good Practice:Always set a

pointer to NULL after delete

Error!

Freememory

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NULL

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References [new]

A reference variable is a pointer that is automatically

dereferrencedwhen it is used. Example:

int x;

int *p = &x; // p points to the int x

int & rx = x; // rx is also pointing to the int x

Difference between the usage of p and rx:

To decrement x, we use --x

To decrement x through p, we use --*p To decrement x through rx, we use --rx

Same syntax as x, as if rx is an alternate name(synonym) of the int x. No need to dereferrencerx

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Reference Examples

x

name content

intRef 456

int x = 456;

int& intRef = x;

intRef++;cout

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Function

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Function

A function is a named block of statements with parameters

SyntaxReturn-typefunction-name( parameters ) {

// body

}

The function gets its input from the caller through parameters

When // body is done, the result ofReturn-type is returned When the block { }is replaced by ;, we have the corresponding

function prototype

// Function definition

intfactorial( int n){

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

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Function Prototype (Declaration)

int factorial( int );

int main( )

{

cout

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Function : Default Argument [new]

Function parameter can be given a default value.

Default value is used if the caller does not supply a value

doubl e l ogar i t hm( doubl e N, double base = 10 ){ . . . Cal cul at es Logbase( N) . . . }

i nt mai n( ){

cout

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Function : Default Argument [new]

Parameters with default values should appear last in

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

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

When calling a function that has default parameters

Only trailing arguments can be omitted

E.g. Given f ( i nt 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 A P i

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Function : Argument Passing

There are three ways of passing an argument into a

function:1. Pass by value

2. Pass by address (or Pass by pointer )

3. Pass by reference

Lets try to define a function swap(a, b) to swap the

parameters a and b

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F i P b l

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Function : Pass by value

void swap_ByValue( int a, int b ){

int temp;

temp = a;

a = b;

b = temp;

}

123

456

123

456

i

j

a

b

56

int main()

{ int i = 123, j = 456;

swap_ByValue(i, j);

cout

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Function : Pass by address/pointervoid swap_ByAdr( int* a, int* b )

{ int temp;

temp = *a;

*a = *b;

*b = temp;

}

123

456

1024

1028

1024

1028

i

j

a

b

57

int main()

{ int i = 123, j = 456;

swap_ByAdr(&i, &j);

cout

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Function : Pass by reference [new]

void swap_ByRef( int& a, int& b )

{ int temp;

temp = a;

a = b;

b = temp;

}

123

456

i

j

a

b

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int main()

{ int i = 123, j = 456;

swap_ByRef(i, j);

cout

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Pass by const reference

Objects may occupy big memory space and thus pass

by value is inefficient. By declaring the parameter to be a const reference, the

function can access the object directly but can notchange it.

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E l f f

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Example of const reference

int count_occurences(char c, const string& s) {

int count = 0;for (int i = 0; i < s.size(); i++) {

if (s[i] == c) count++;

}

return count;

}

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F i Si [ ]

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Function Signature [new]

Compiler recognizes a function by its function signature

which includesFunction name + data types of parameters

Example:

f act or i al ( i nt )

sqr t ( doubl e)

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Note:Function return type is not part of the function signature

F ti O l di [ ]

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Function Overloading [new]

C++ allows multiple functions to have the same name

provided their function signatures are different. Thisfeature is called function overloading

Besides having the same function name, the numbersand/or types of the parameters of these functions aredifferent

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F ti O l di [ ]

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

if (a > b) return a;else return b;

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

return max( max(a, b), c);}float maximum(float a, float b) //Ver.3{ // maximum(float , float )

if (a > b) return a;

else return b;}

maximumfunction has been overloaded

Note the difference in number and data type of parameters