C++ Chapter 6-pointers about pointers in programming

about pointers in programming

1. Pointer In C++
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2. Pointer
•A pointer is a variable that used to store a
memory address of other variable.
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Pointer operator
1. Indirection (dereference) operator ‘*’
2. Unary (reference) operator ‘&’.

3. 1. Reference (unary) & operator
The address that locates a variable within memory is
what we call a reference to that variable.
The unary operator returns the address of the memory
where a variable is located.
Any variable preside by & is read as “Address of …“
Example
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X = 25;
v = X;
P = & x;

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X
1775 1776 1777
25 1776
25
Pv
&
The values contained in each variable after the execution of
the above code segment, are shown in the following diagram
Variable X contains both address and actual value 25
Variable v contains actual value of X
A Variable that stores the reference of other variable is called
Pointer: P stores address of X so, P is pointer

5. 2. DEREFERENCE ( INDIRECTION ) * OPERATOR
A Variable that stores the address of other variable is called Pointer.
Using a pointer we can directly access the value stored in the
variable which it points to.
Dereference operator will literally translated as <Value pointed
by…>
Example:- This will reads as
<val equal to value pointed by p>
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val = *P

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val would take a value 25 since P is 1776 and <the
value pointed by 1776> is 25.
Notice the difference b/n & and *:
 & is reference and read as "address of”
 * is the dereference and read as <"value pointed by“>
val = *P

7. Class activity
•Look at the diagram below which of comparison statement will
return true?
A. (P ==25) B. (P==1776)
C. (val == 1776) D. (val == 25)
E. (*p ==25)
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8. pointer declaration
The general form of declaring pointer is:-
Data type is the base type of the variable pointed by the
pointer and variable_name is the name of the pointer
variable .
For example,
There are three declaration of pointers each of them
intended to different data type
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Data type * variable_name;
int * number;
char * character;
float * greatnumber;

9. Example
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#include <iostream>
using namespace std;
int main () {
int firstvalue, secondvalue;
int * mypointer;
mypointer = &firstvalue;
*mypointer = 10;
mypointer = &secondvalue;
*mypointer = 20;
cout << "firstvalue is " << firstvalue endl;
cout << "secondvalue is " << secondvalue << endl;
return 0;
}

10. Pointer initialization
When declaring pointers we may want to explicitly specify which
variable point to:
We can initialize pointer into either
Reference or address of other variable
Null or Zero(0) Pointer
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int number;
int *tommy = &number;
int number;
int *tommy;
tommy = &number;
int number;
int *tommy;
*tommy = &number;
Wrong
int *tommy ;
tommy = 0;
tommy = Null;
Null Pointer
Initialization

11. NULL POINTER:
A null pointer is a regular pointer of any
pointer type which has a special value that
indicates it is not pointing to any valid
reference or memory address.
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12. Class activity
•Look at the code and write
description of each line
statements Line-1 To Line-3
•For Line-4 and Line-5 write
plaintext equivalent of their
meaning
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Line-1:
 
int * P ;
Line-2: int c=100;
Line-3 : int x;
Line-4 : P=&c;
Line-5 : x=* P;
?

13. Example
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#include<iostream>
using namespace std;
int main ()
{
 
       
int *p, c=200, x;
 
         
p=&c;
 
x=*p;
 
          
cout << " Address of the memory of p: " << p << endl;
 
          
cout << " The contents of the pointer p : " << *p << endl;
 
          
cout << " The contents of the variable x : " << x << endl;
system(" pause " );
            return (0);}