Pointer In C++ Programming

Definition

A pointer is a variable that holds a memory address, usually the location of another variable in memory. Pointer variable hold address of it’s own type variable i.e. an integer pointer will hold address of integer type variable and a character pointer will hold address of character type variable.

Use of pointer

1.    Pointers provide the means through which the location of a variable can be directly accessed  and hence can be manipulated in the way as required.

2.     Pointers support c++’s dynamic allocation routines.

Disadvantages

1.      Un-initialized, or wild pointers can cause system to crash.

2.      It is easy to use pointers incorrectly, causing bugs that are very difficult to find.

Syntax for pointer declaration

      Data_type       * variable_name; // * can be on right side

      Data_type *       variable_name; // * can be on left side

      Data_type    *    variable_name; // * can be on center

Declaration of pointers

int           *iptr;     // integer pointer

char        *cptr;    // character pointer

float        *fptr;    // float pointer

double    *dptr;   // double pointer

long        *lptr;    // long pointer

Initialization of pointers

int i=25;

ptr=&i;

char ch=’a’;

cptr =&ch;

float flt = 3.14;

fptr = &flt;

double dbl = 1.23622;

dptr = &dbl;

long lg = 123452;

lptr = ≶

The two special operator (*  and  &) are used with pointers. The & is a unary operator that returns the memory address of its operand. * is the dereference operator. It is also called as “value at the address of”. It returns the value present at the address which is hold by pointer.

Example: Pointer 

#include<iostream.h>

#include<conio.h>

void main()

{

   int a =10;

   int *b = &a;

   

   cout<<"\n value of  a "<<a;

   cout<<"\n value of  a "<<*b;

   cout<<"\n address of a "<<&a;

   cout<<"\n address of a "<<b;

   getch();

}

Output

Video 

Example: Pointer to Pointer

#include<iostream.h>                       

#include<conio.h>

void main()
{
int a=10,*b,**c;
b=&a;
c=&b;

cout<<"\n value of a "<<a; //value of a
cout<<"\n value of a "<<*b; //value of a
cout<<"\n value of a "<<**c; //value of a

cout<<"\n value of b "<<*c; //address of a, because value of b is address of a
cout<<"\n value of b "<<b; //address of a, because value of b is address of a

cout<<"\n address of b "<<&b; //address of b
cout<<"\n address of b "<<c;  //address of b, c is pointer to pointer variable which hold a pointer                                                          variable address that is *b
cout<<"\n address of c "<<&c; //address of c
getch();
}

Output

Pointer Arithmetic

Only two arithmetic operation, addition and subtraction may be performed on pointers. When we add 1 to a pointer, we are actually adding the size of whatever the pointer is pointing at, i.e. each time a pointer is incremented by 1. It points to the memory location of the next element of its base type.

Example

int *ptr; //current address is  => 1001

ptr++;   // new address will be => 1003
ptr--;     // new address will be => 1001

A pointer holds the address of the very first byte of the memory location where it is pointing to. The address of first byte is known as base address.

Example: Arithmetic operation on pointer

#include<iostream.h>

#include<conio.h>

void main()

{

int i=10;

int *ptr=&i;

cout<<"address of i "<<ptr<<endl;

ptr++;

cout<<"address of location next to i "<<ptr<<endl;

ptr--;

cout<<"address of i again "<<ptr<<endl;

++ptr;

cout<<"address of location next to i "<<ptr<<endl;

--ptr;

cout<<"address of i again "<<ptr<<endl;

getch();

}

Output

Video

Increment And Decrement of Variable Values By Pointer

#include<iostream.h>
#include<conio.h>

void main()
{
int n=44;
int *ptr=&n;

cout<<"\n real value of n "<<*ptr;
++*ptr;
cout<<"\n vlaue of n after pre increment "<<*ptr;
(*ptr)++;
cout<<"\n value of n after post increment "<<*ptr;
--*ptr;
cout<<"\n value of n after pre decrement "<<*ptr;
(*ptr)--;
cout<<"\n value of n after post decrement "<<*ptr;

getch();
}

Output

Arithmetic operation (Addition, Subtraction, Division, Multiplication) by pointer

#include<iostream.h>

#include<conio.h>

void main()

{

int a,b;

int *p,*q;

p=&a;

q=&b;

cout<<"Enter value of a ";

cin>>*p;

        

 cout<<"Enter value of b ";

 cin>>*q;

int add=*p+*q;

cout<<"\n Sum is "<<add;

int sub=*p-*q;

cout<<"\n substraction is "<<sub;

int product=*p * *q;

cout<<"\n Product is "<<product;

int div=*p / *q;

cout<<"\n Division is "<<div;

getch();

}

Output

Pointer With If Else

#include<iostream.h>                     
#include<conio.h>
void main()
{
int a,b;
int *p,*q;
p=&a;
q=&b;

cout<<"Enter value of a ";
 cin>>*p;
 cout<<"Enter value of b ";
cin>>*q;

if(*p>*q)
cout<<a<<" is greater ";
else
cout<<b<<" is greater ";

getch();
}

Output

Video

Reverse Digits of a Multi Digit Number By Pointer

#include<iostream.h>

#include<conio.h>

void main()

{

int num, remainder, sum=0;

int *ptr;

cout<<"Enter a multi digits number ";

cin>>num;

ptr=&num;

while(*ptr>0)

{

remainder = *ptr%10;

sum = sum*10+remainder;

*ptr=*ptr/10;

}

cout<<"Reverse number is "<<sum;

getch();

}

Output

Pointer With Array

#include<iostream.h>
#include<conio.h>
void main()
{
int a[5];
int i,*p;
p=a;
//or
//p=&a[0];

cout<<"\n Enter Elements of Array "<<endl;
for(i=0;i<5;i++)
cin>>*(p+i);

cout<<"\n Array Elements are \n";
for(i=0;i<5;i++)
cout<<*(p+i)<<endl;

getch();
}

Output

Video

Bubble Sort By Pointer Array

#include<iostream.h>
#include<conio.h>

void main()
{
int a[5],i,j,temp,*p;
p=a;

cout<<"\n Enter Elements of Array \n";
for(i=0;i<5;i++)
cin>>*(p+i);

for(i=0;i<5;i++)
{
for(j=0;j<(5-i-1);j++)
{
if(*(p+j)>*(p+(j+1)))
{
temp=*(p+j);
*(p+j)=*(p+(j+1));
*(p+(j+1))=temp;
}
}
}

cout<<"\n Array After Sorting "<<endl;
for(i=0;i<5;i++)
cout<<*(p+i)<<" ";

getch();
}

Output

Video

Pointer With Two D Array With Initialization Method

#include<iostream.h>
#include<conio.h>

void main()
{
int a[][3]= {
    {1,2,3},
                     {4,5,6},
                     {7,8,9}
    };
   int *p = &a[0][0];

   cout<<"\n Matrix elements are \n";
for(int i=0; i<3; i++)
   {
    for(int j=0; j<3; j++)
      {
      cout<<*(*(a+i)+j)<<" ";//a[i][j]
      }
      cout<<endl;
   }
getch();
}

Output

Video

Pointer With Two D Array By User Input Method

#include<iostream.h>
#include<conio.h>
void main()
{
int (*a)[3];//3 is the number of columns
a=new int[3][3];//assigning memory to element of each row
int i,j;

 cout<<"\n Enter Elements of Matrix \n";
for(i=0;i<3;i++)
{
for(j=0;j<3;j++)
{
cin>>*(*(a+i)+j); //a[i][j]
}
}

 cout<<"\n Matrix Elements are "<<endl;
for(i=0;i<3;i++)
{
for(j=0;j<3;j++)
{
cout<<*(*(a+i)+j)<<" ";
}
cout<<"\n";
}
getch();
}

Output

Pointer With String

String can be declared with the help of pointer. There various ways through which we can declare string with the help of pointer. String with pointer is declared by char pointer only. All the method to declare a string with pointer we represented in below shown program.

#include<iostream.h>
#include<conio.h>
void main()
{
   char *string1="Good Morning";
   cout<<string1<<endl;

   char string2[]="welcome to school";
   char *tempstring = string2;
   cout<<tempstring<<endl;

   char str[]="Hello how are you";
   tempstring = &str[0];
   cout<<tempstring<<endl;
 
   char *ptr="c++ programming";
while(*ptr!='\0')
{
    cout<<*ptr;
   ++ptr;
  }
   getch();
}

Output

Assignment of Char Pointer To One Another

Assignment of one string to another is not possible while assignment of one pointer string to another pointer string is possible. We can see it in below example.

#include<iostream.h>
#include<conio.h>
void main()
{
char string1[]="hello";
char string2[10];
char *ptr1="Good Morning ";
char *ptr2;

//string2=string1;//assignment of one string to another is not possible
ptr2=ptr1; //assignment of one pointer string to another pionter string is possible

cout<<"First string\t:"<<string1<<"\n";
cout<<"Copied String\t:"<<string2<<"\n";//will show blank, because string not copied
cout<<"First Pointer String\t:"<<ptr1<<"\n";
cout<<"Copied Pointer string\t:"<<ptr2<<"\n";

getch();
}

Output

String Array By Pointer

We can declare an array of strings by pointer in C++. For this we have to take an array of character pointer (char *).

In below example we declare a character array names (char *names[]). In it we can see that each element is string literal. String literal always points to the base address of the first character. So the base type of each element of the names array is a pointer to char or char *.

#include<iostream.h>
#include<conio.h>
void main()
{
char *names[] ={"amir","shil","neelam","iram"};
for(int i=0; i<4; i++)
   {
cout<<names[i]<<"  ";
   }
   getch();
}

Output

String Array By Pointer By User Input Method

Neither we can insert directly a STRING into STRING ARRAY nor we can assign a STRING to another STRING.

For this first we have to read a STRING. Than we will assign this STRING to a CHARACTER POINTER. After that this CHARACTER POINTER will assign this STRING to STRING ARRAY.

We can implement this entire process like as shown in below program.

#include<iostream.h>
#include<conio.h>
#include<stdio.h>
#include<string.h> //for strlen() function

void main()
{
  char *namesArray[5];
  char tempname[15];
  char *pointer;

for(int i=0; i<5; i++)
{
  cout<<"\n Enter a Name ";
  //reading single name by user in tempname variable
  gets(tempname);

  //getting length of string stored in tempname by strlen() function
  int length = strlen(tempname);

  //assigning dynamic memory to pointer by new operator of size length+1
  pointer = new char[length+1];

 //copying tempname string into pointer string, because string directly can not assign to another string
 strcpy(pointer, tempname);

 //assigning pointer string to namesArray's ith position character pointer
 namesArray[i]=pointer;
}

cout<<"\n Names You Entered are"<<endl;
for(int i=0; i<5; i++)
{
  cout<<names[i]<<endl;
}
getch();
}

Output

Digits Sum of A Multi Digit Number By Pointer To Function

#include<iostream.h>
#include<conio.h>

int digitSum(int *num)
{
int remainder, sum=0;
while(*num>0)
{
remainder=*num%10;
sum=sum+remainder;
*num=*num/10;
}
return sum;
}

void main()
{
int number;
cout<<"\n Enter A Multidigit Number  ";
cin>>number;
cout<<"\n Number Digit Sum is : "<<digitSum(&number);
getch();

}

Output

Function With Pointer Return Type

#include<iostream.h>

#include<conio.h>

//Function Prototype

int * reverseDigit(int *);

void main()

{

            int number;

            cout<<"\nEnter A Multi Digit Number : ";

            cin>>number;

            int *ptr, tempNumber;

            tempNumber=number;//Storing a temprary copy of orignal number

            ptr=reverseDigit(&number);//Function Call

 if(*ptr==tempNumber)

 {

          cout<<"\nNumber Is Palindrome ";

 }

else

{

          cout<<"\nNumber Is Not Palidrome";

}

           getch();

}

//Function Definition

int * reverseDigit(int *num)

{

            int remainder, sum=0;

            while(*num>0)

            {

                        remainder=*num%10;

                        sum=sum*10+remainder;

                        *num=*num/10;

            }

            return &sum;

}

Output

Video

Memory Allocation

Each data element or variable is provided some memory; and this process of allocating memory is known as memory allocation. This process is of two types.

•      Static Memory Allocation 

•      Dynamic Memory Allocation

Static Memory Allocation

When the amount of memory to be allocated is known before handed and the memory is allocated during compilation itself, is known as static memory allocation. 

Ex. int i , In this case the compiler knows that 2 bytes will be allocated to i, because it is an integer variable.

Dynamic Memory Allocation

The process of allocating memory at the time of execution is called dynamic memory allocation. The allocation and release for this memory space can be done with the help of some operators Ex. new, delete.  The new operator allocates memory dynamically and returns a pointer storing the memory address of the allocated memory. The operator delete free the memory pointed by a pointer.

Free Store

It is a pool or heap of Un-allocated memory provided to a program so that it can utilize during execution. The free store memory is without name. Objects allocated on the free store are manipulated indirectly through pointers.

Another aspect of free store is that the allocated memory is uninitialized. The free store memory is allocated through the use of new operator and de-allocated through delete operator.

Free store memory is dynamically allocated during run time and static memory allocation takes place during compile time. 

Memory Leaks

If the objects, that are allocated memory dynamically, are not deleted using delete, the memory block remains occupied even at the end of the program. Such memory blocks are known as orphaned memory blocks. This orphaned memory blocks when increase in number, bring an adverse effect on the system. This situation is known as memory leak. The possible reason for this are:

1. A dynamically allocated object not deleted using delete.

2. Delete statement is not getting executed because of some logic error.

3. Assigning the result of a new statement to an already occupied pointer.


The Memory Leak Can Be Avoided By

1. Making sure that a dynamically allocated object is deleted.

2. A new statement stores its return value (a pointer) in a fresh pointer.

Dynamic Single Dimension Array

#include<iostream.h>

#include<conio.h>

void main()

{

            int size;//Static Memory Allocation

            cout<<"\nEner Size of Array : ";

            cin>>size;

            //Dynamic Memory Allocation

            int *Array=new int[size];

            cout<<"\nEnter Array Elements"<<endl;

            for(int i=0;i<size;i++)

           {

               cin>>Array[i];

           }

           cout<<"\nArray Elements Are \n\n";

           for(int i=0;i<size;i++)

           {

               cout<<Array[i]<<"\t";

           }

            getch();

}

Output

Dynamic Double Dimension (2D) Array

#include<iostream.h>
#include<conio.h>

void main()
{
int *Array,raw,column,i,j;

cout<<"Enter Number of Rows : ";
cin>>raw;
cout<<"Enter Number of Columns : ";
cin>>column;

//Declaration of Dynamic Array
Array=new int[raw*column];

cout<<"\nEnter Elements of Matrix "<<endl;
for(i=0;i<raw;i++)
{
for(j=0;j<column;j++)
{
cin>>Array[i*column+j];
}
}

cout<<"\nMatrix Elements Are "<<endl;
for(i=0;i<3;i++)
{
for(j=0;j<3;j++)
{
cout<<Array[i*column+j]<<" ";
}
cout<<endl;
}

getch();
}

Output