lecture 12 pointer

7/30/2019 Lecture 12 Pointer

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BITG 1113:Pointer

LECTURE 12


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Objectives:

To understand the concept of pointer.

Declaration and Assignment of a Pointer.

Arithmetic Operation using Pointer.

Pointer to pointer.

Pointers and functions.

Relationship between a Pointer and anArray.

Pointer to structure.


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Introduction

A pointer is a derived type. Its value may be

any of the addresses available in the computer

for storing and accessing data.

In a computer, every process is stored in a

compartment or small area inside the memory.

These memories have their own addresses.

By using this address, the computer canidentify where a data or an instruction is stored

physically in a computer.


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Introduction

Variable declaration :

int nilai;

Only shows the value that is stored inside

nilai, without knowing where it is stored.

The name of the variable is an @ for theaddress where it is stored.

Each time, the variable being used, the

computer will translate the name of that

variable to its address.

By using pointer, the programmer can

determine the address for any location

where a value is stored.


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Pointer Declaration and Definition

Syntax :

type * identifier;

Example :

1.char a=A;

char *p; OR

p = &a; char *p = &a;

2. double b=2.5;

double *q; OR

q = &b; double *q=&b;

The type of pointer indicates

the type of value it refers.


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int x=7;int *p;

p = &x;

Suppose that the address of the int variable x is 9640

x 7 9640p

9640

the variable p

points to x

9642

Pointer Declaration and definition


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#include

void main()

{

int pertama=8;

int *pAlamat;

pAlamat = &pertama;

cout


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#include

int main()

{

int pertama=7;

int *pAlamat;

pAlamat = &pertama;

cout


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The following program slice swaps thecontents of the variables char1 and char2

but uses the address and dereferencing

operators to do so.

Line #includemain()

{

1 char char1 = A;

2 char char2 = Z;

3 char temp;

4 char* charPtr;

5 charPtr = &char1;

6 temp = *charPtr;

7 *charPtr = char2;

8 char2 = temp;

}

Example


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A Z

char1 char2 temp

1293 7757 2131

line

1 char char1 = A;2 char char2 = Z;

3 char temp;


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A Z

char1 char2 temp

1293 7757 2131

line

4 char* charPtr;

charPtr

4455


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A Z A

char1 char2 temp

7757 2131

line

6 temp = *charPtr;

1293

charPtr

44551293


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Z Z A

1293 7757 2131

line

7 *charPtr=char2;

1293

4455

char1 char2 temp charPtr


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Z A A

char1 char2 temp

1293 7757 2131

line

8 char2 = temp;

1293

charPtr

4455


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O H 941

c d p1

6940 2131

6940

p2

4455

line

5 temp = p1;

941

temp

941


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O H 6940

c d p1

6940 2131

6940

p2

4455

line

6 p1 = p2;

941

temp

941


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O H 6940

c d p1

6940 2131

941

p2

4455

line

7 p2 = temp;

941

temp

941

line

8 cout


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Arithmetic Operation Using Pointer

Arithmetic operation can also be done using

pointer.

A pointer will take the value stored at the

address that is kept by the pointer andcompute them just like operations on

normal variables such as add, multiply,

divide, minus and unary operator.


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//Example:

#include

void main()

{

int nombor = 6, jumlah;

int *pnum=&nombor;

jumlah = *pnum * *pnum;

cout


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Pointer to pointerSo far the pointers we have been using have

pointed directly to data. It is possible and

often with advanced data structures necessary

to use pointers that point to other pointers.

eg: *p dereferenced once

**q dereferenced twice


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#includemain() {

int a;

int *p;

int **q;

a = 58;

p = &a;

q = &p;

cout


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Pointers and functions

C++ provides two ways to pass parameters tofunctions : pass by value and pass by reference.

When we passed by reference, C++ passes the

address of the parameter variable, and theparameter name becames an alias for the variable.

We can add an alternative to pass by reference:

pass a pointer and use it to change the originalvariable.


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void main()

{//Pass by reference

int a = 5;

int b = 7;

exchange (a,b);}

void exchange(int& x, int& y)

{

int temp = x;x=y;

y= temp;

return;

}//exchange

Example

7 5

a b

x y

5

temp


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Examplevoid main()

{//Passing pointers

int a = 5;

int b = 7;

exchange (&a,&b);}

void exchange(int* px, int* py)

{

int temp = *px;*px=*py;

*py= temp;

return;

}//exchange

7 5

a b

px

y

5

temp

py


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Relationship between aPointer and an Array

A pointer and an array have a close

relationship.

In C++ Programming Language, the name ofan array without the index is the first address

of that array. In other words, the name of an

array is actually a pointer to that array.

So, the name of an array can be used to beset as an initial value for a pointer.

The name of an array will refer to the

address of the first element of that array.


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The difference between a pointer and an arrays

name is, a pointer points to any address in the

memory but the name of an array points only to

the first element of that array and it is fixed.

Example :

double value[10];double *pValue = value;

From the declaration above, *pValue will store

the first element of array value which is theaddress of value[0].



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To achieve the next element in an array, use thisformula :-

*( penuding + i )

where , i represents the location of the element

in an array.

Example :

double value[5]={2.5,4.1,5.6,4.7,4.3};

double *pValue = value;

cout


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Example of program that use anarray and index

#include main()

{

const int saiz = 5;

int i;

int gred[saiz]={98,88,90,65,83};

for( i = 0; i


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From the example, each element in arraygred can be reach using pointer :

Array Pointer Value in Array

gred[0]

gred[1]

gred[2]

gred[3]

gred[4]

*pNilai

*( pNilai + 1 )

*( pNilai + 2 )

*( pNilai + 3 )

*( pNilai + 4 )

98

88

90

65

83



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Example :

double value[5]={2.5,4.1,5.6,4.7,4.3};

double *pValue = &value[1];

cout


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Structure can be accessed through pointers.

Example : use SAMPLE structure with pointers.

The first thing is define a pointer for the

structure as shown below.

Refer to whole structure

Pointer to Structure


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The parentheses are absolutely necessary

because the precedence priority of the

member operator is higher than the priority of

the indirection operator.

If the parentheses are not used, C++ applies

the dot operator first and the asterisk operator

next.

In other words, *ptr.x is interpreted as

*(ptr.x)



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Another operator that eliminates the problem

with pointers to structures the selectionoperator.

The selection operator is at the same level in the

Precedence Table as the member operator.

The token for the selection operator is an arrow

formed by the minus sign and the greater than

symbol (->).

The token is placed immediately after the pointer

identifiers and before the member to be

referenced.

Selection Operator


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(* pointerName) . fieldName

SAME AS

pointerName -> fieldName

Selection Operator


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Selection Operator

lecture 12 pointer

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