C++ 39: Pointers

 Variables: 

• The Variable is a memory location with specified name.
• Every memory location has a unique address That means every variable have unique address.
• The variable is used to store values.

Pointers

• The pointer is variable which can be used to store address of  a variable or memory location or an object.
• The pointer always points to the memory location or object whoose address is currently present in the pointer. 
• The pointers are mainly used to reserve and releze the memory dynamically (i.e during runtime at the execution of the program).
• Also, pointers are used to perform following operations.
• To pass array as argument
• To return multiple values from a function 
• A pointer can be defined using syntax:

Syntax :

        data_type *poiter_name;

Storing address of a variable in the pointer:

• The "address_of" (i.e. &) operator returns the address of the varable.
• The address of variable is unsigned integer(i.e. the address cannot be negative) so, to print the address we have to use the format specifier %u in C programming.
• The address of the variable can be stored in the pointer by using following syntax:
• Syntax:
• pointer_variable = &variable;

Example:

#include <iostream>
using namespace std;
int main()
{
    int a = 5;  
    int *p = &a; //pointer variable
    cout << "a = " << a << endl;
    cout << "*p = " << p << endl;
    (*p)++;
    cout << "a = " << a << endl;
    cout << "*p = " << *p << endl;
    return 0;
}

Output:

a = 5
*p = 0x61fe14
a = 6
*p = 6

Example 2:

#include <iostream>
using namespace std;
main()
{
    int a = 5, b = 10, *p, *q;

    p = &a;
    q = &b;
    int x = *p + *q;
    cout << " p = " << p << endl;
    cout << " q = " << q << endl;
    cout << "*p = " << *p << endl;
    cout << "*q = " << *q << endl;
    cout << "x = " << x << endl;
    int y = *p * *q;
    cout << "y = " << y << endl;
    return 0;
}

Output:

p = 0x61fe04
 q = 0x61fe00
*p = 5
*q = 10
x = 15
y = 50

Example 3:

#include <iostream>
using namespace std;
main()
{
    int a = 2, *p, *q;
    p = &a;
    q = p;

    cout << a << "\t" << *p << "\t" << *q << endl;
    a++;
    (*p)++;
    (*q)*= 2;

    cout << a << "\t" << *p << "\t" << *q << endl;
    return 0;
}

Output:

2       2       2
8       8       8