Learn c++ Pointers with Examples

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This C++ Tutorial Covers


  • Pointers Syntax, declaration, initialization 
  • Pointers with address (&) and asterisk (*) operator
  • Errors may found while working with pointers
  • Basic example pointers C++ program
  • Relation of Asterisk and address operator

What is a Pointer in C++ Programming?
A pointer is a variable which stores or points to memory address of a variable. Pointer can access indirectly the value of a variable using its address. Both pointer and variable will be of same data type. 

Declaration of a Pointer

Like other variables pointer declares in the same way. First write the data type then its name with asterisk before pointer's variable name.
Declaration Syntax
int *ptr;
where ptr is a pointer of integer and will point to an integer address variable normally we read it from right to left as ptr is a pointer to an integer value
Its is recommend that while declaring a pointer use the short word _ptr after variable name which will increase the readability of program.

Initialization of a Pointer

Like other variables pointers can be initialize at the time of declaration or after it using assignment method.
It initialize with value 0 or NULL and corresponding data type.
For example
int *ptr, a=5; 
ptr=NULL; and ptr=0;   both have same meaning

A pointer which points to a NULL value called as a NULL Pointer.  The point to be noted here 0 is an interger value but pointer stores address only if we do int *ptr=7; or any other integer value then error occurred.  

Students should Remember that 0 is the only integer value by which  
Pointer with Unary Operator & 
To get the address the unary operator & known as address operator is used.
for example
int *ptr;
int x=5;
ptr=&x; //  assigns the address of variable x to pointer ptr
we said that ptr is a pointer pointing to memory address of variable x and indirectly pointer can access the value of variable x. 

Asterisk * Operator With Pointer

The * operator is usually know as de-refrence operator used to get the value of variable using pointer.
For Example
To get Value of a variable
int *ptr; // Don't confuse here it is pointer declaration 
 x=10;
ptr=&x;
cout<<ptr; // will print the address of x
cout<<*ptr; // will print the value of x = 10;

Using on left side

*ptr=15;
cout<<*ptr; //  now will print 15;
 now the memory address of x value has changed replaced by 15

To take input 

cin>> *ptr; // it will take input 
now the memory address of x value has changed by what value is entered

Relation between * and address operator &

Both operators cancel the each other value and the value of variable is provided as result.
For example
int *ptr, a=5;
ptr=&a;
Let address of a= 0X100; so ptr=0X100;
    cout<<*ptr<<endl;      // 5
    cout<<ptr;                    // 0X100
    cout<<*&ptr<<endl;   // 0X100
    cout<<&*ptr<<endl;   // 0X100

    cout<<*(&ptr)<<endl; // 0X100
    cout<<&(*ptr)<<endl; // 0X100

Errors while working with pointers 
  • De-referencing  a NULL Pointer is an error
           int   *nPtr=NULL;
    cout<<  *nPtr;  // Error
  • Assigning a pointer to different data type
    int n;  double *dPtr;
             dPtr=&n;  // error: cannot convert int to double
  •  Trying to de-refrence a non pointer variable
Pointers Example program which displays different ways to deal with pointers
Compiler Used CodeBlocks C++ Compiler

#include<iostream>
using namespace std;

int
main()
{

int
*ptr; double a=222;
int
x=10;
// ptr=&a; error
ptr=&x;
cout<<"Address of ptr = "<<ptr<<"\n\n\n";
cout<<"Defrefrecned to get Value of s *ptr= " <<*ptr<<"\n\n\n";
*
ptr=50;

cout<<"Changing value using *ptr=50 "<<"\n\n\n";
cout<<"Now Defrefrecned to get Value of x *ptr= "<<*ptr<<"\n\n\n";

int
*nPtr=NULL;
//error
// cout<<*nPtr;

cout<<"NULL Pointer "<<&nPtr<<"\n\n\n";

cout<<"Taking Input in pointer Using cin>> *ptr : ";
cin>>*ptr;

cout<<"Input Value = "<< *ptr<<"\n\n\n";
return
0;
}

read also: C++ Pointer example with pass by reference

Output 



See also: Difference b/w pass by value and pass by reference with C++ example

Recommendation: Copy the above code, edit it and examine the output of program. It will be very helpful for good learning.

See more Simple examples here of C++ programs
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