Pointers in c++

POINTERS INC++
BY -
SAI TARLEKAR

Points
 Introduction.
 Declaration and initialization of pointers.
 Small program.
 Thumb rule.
 Pointer Variable.
 Pointer Arithmetic.
 Reference Variable.
 Reference as function arguments

What is a Pointer???
 A pointer is a variable which holds the memory address
of another variable.
 This memory address is the location of another variable
where it has been stored as memory.
 Therefore if a variable contains the address of another
variable is said to point to the second.

Declaration and Initialization of
Pointers
 Syntax : Datatype *variable_name;
eg. int *x;
float *y;
char *z;
eg. int x = 10;
int *ptr = &x;
 Now ptr will contain address where the variable x is stored in memory.

int *ptr;
This tells the compiler three things about ptr:-
1) The (*) tells that the variable ptr is a pointer
variable.
2) Pointers need a memory location.
3) Pointers points to a variable of type int.

More info….
1) A pointer that is not initialzed is called as wild pointer
because you have no idea what it is pointing to.
2) A pointer whose value is zero is called as null pointer.
3) Void pointer - void pointer is a special type of pointer
that can be pointed at objects of any data type. A void
pointer is declared using data type void.

Thumb rule of pointers:-
1) Type must be same to the variable whose address is going
to pass to the pointer.
2) When you want to pass the address of the variable use ‘&’
before the variable name.
3) When you want to pass the value of the variable use ‘*’
before the pointer.

Pointer operator
 A pointer operator or a pointer variable is represented by a
combination of asterisk(*) with a variable name.
Syntax:-
data_type *pointer_variable;
eg. If a variable of character data type and also declared as *
(asterisk) with another variable it means the variable is of type
“Pointer to character”.
char *ptr;
where ptr is a pointer variable which holds the address of an
character data type.

Address Operator
 An address operator can be represented by a combination of and (ampersand)
with a pointer variable.
 The and is a unary operator that returns the memory address of its operand.
Syntax:-
data_type variable1;
data_type variable=&variable1;
Eg:-
int x;
int *ptr=&x;
It means that ptr receives the address of x;

Pointer Arithmetic
 Two arithmetic operations, addition and subtraction, may be
performed on pointers. When we add 1 to a pointer, we are
actually adding the size of data type in bytes, the pointer is
pointing at.
Eg. int *x; x++;
 If current address of x is 1000, then x++ statement will increase x
by 2(size of int data type) and makes it 1002, not 1001.

Data is stored in contiguous memory cell.
The Number of memory cells required to store a
data item depends on the type of data item
Char 1 byte
Integer 2 byte
Floating 4 byte
Double 8 byte

REFERENCE VARIABLE
A reference variable is a name that acts as an alias or an alternative name,
for an already existing variable.
Syntax:-
Data type &variable name = already existing variable;
Eg. int num=10;
int & sum = num; // sum is a reference variable or alias name for
num
NOTE: Both num and sum refer to the same memory location. Any changes made to the sum
will also be reflected in num.
10
sum
num

void cube(int &x)
{
x= x*x*x;
}
void main()
{
int y=10;
cout<<y<<endl;
cube(y);
cout<<y<<endl;
}
x
In the above program reference of y is passed. No separate
memory is allocated to x and it will share the same memory
as y. Thus changes made to x will also be reflected in y.
OUTPUT:
10
1000
REFERENCE AS FUNCTION ARGUMENTS
y
100

Program
#include<iostream.h>
#include<conio.h>
swap(int *,int *)
void main()
{
int a,b;
cout<<"nEnter value for A : ";
cin>>a;
cout<<"nEnter value for B : ";
cin>>b;
cout<<"nnBefore Swapping : ";
cout<<"nttta = "<<a;
cout<<"ntttb = "<<b;
swap(&a,&b);
cout<<"nnAfter Swapping : ";
cout<<"nttta = "<<a;
cout<<"ntttb = "<<b;
getch();
}
swap(int *x,int *y)
{
int temp;
temp=*x;
*x=*y;
*y=temp;
}

Pointers in c++

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Pointers in c++