How to read pointers

Hi all,
This is my first post. Many peoples have problems on pointers.
This post will help to understand pointers.

1. char a;
   Read : 'a' is a variable of char type.

2. char *ptr;
   Read : 'ptr' is a pointer to char.

3. char* ptr[5];
   Read : 'ptr' is an array of 5 pointers to a char.
   Note : The precedence rules say that the square brackets([]) are higher than the asterisk(*).
   Ex:
   int *ptr1 = NULL;
   int *ptr2 = NULL;
   int *ptr3 = NULL;
   int *ptr4 = NULL;
   int *ptr5 = NULL;
   char *ptr[5] = {ptr1, ptr2, ptr3, ptr4, ptr5};

4. int ** ptr2;
   Read : 'ptr2' is a pointer to pointer to int
   Ex:

int a = 4;
int *ptr1 = &a;
int **ptr2 = &ptr1;

cout << "\n a : " << a;
cout << "\n Address of a : " << &a;
cout << "\n ptr1 : " << ptr1;
cout << "\n *ptr1 : " << *ptr1;
cout << "\n ptr2 : " << ptr2;
cout << "\n *ptr2 : " << *ptr2;
cout << "\n **ptr2 : " << **ptr2;

Output:

a : 4
Address of a : 0040F8D0
ptr1 : 0040F8D0
*ptr1 : 4
ptr2 : 0040F8C4
*ptr2 : 0040F8D0
**ptr2 : 4

1. const int *ptr; Read : 'ptr' is a pointer to const int Ex: const int a = 4; const int *ptr = &a;

cout << "\n a : " << a;
cout << "\n Address of a : " << &a;
cout << "\n ptr : " << ptr;
cout << "\n *ptr : " << *ptr;

Output:

a : 4
Address of a : 0040F8D0
ptr : 0040F8D0
*ptr : 4

1. const int **ptr2; Read : 'ptr2' is a pointer to pointer to const int Ex: const int a = 4; const int *ptr1 = &a; const int **ptr2 = &ptr1;

cout << "\n a : " << a;
cout << "\n Address of a : " << &a;
cout << "\n ptr1 : " << ptr1;
cout << "\n *ptr1 : " << *ptr1;
cout << "\n ptr2 : " << ptr2;
cout << "\n *ptr2 : " << *ptr2;
cout << "\n **ptr2 : " << **ptr2;

Output:

a : 4
Address of a : 0040F8D0
ptr1 : 0040F8D0
*ptr1 : 4
ptr2 : 0040F8C4
*ptr2 : 0040F8D0
**ptr2 : 4

1. char * const * ptr2; Read : ptr2 is a pointer to const pointer to char Ex: char a = 'x'; char *const ptr1 = &a; char * const * ptr2 = &ptr1;

cout << "\n a : " << a;
cout << "\n Address of a : " << &a;
cout << "\n ptr1 : " << ptr1;
cout << "\n *ptr1 : " << *ptr1;
cout << "\n ptr2 : " << ptr2;
cout << "\n *ptr2 : " << *ptr2;
cout << "\n **ptr2 : " << **ptr2;

Output:

a : x
Address of a : 0040F8D0
ptr1 : 0040F8D0
*ptr1 : x
ptr2 : 0040F8C4
*ptr2 : 0040F8D0
**ptr2 : x

1. const int * const * ptr2; Read : ptr2 is a pointer to const pointer to const int Ex: const int a = 10; const int * ptr1 = &a; const int * const * ptr2 = &ptr1;

printf("\n a : %d ", a);
printf("\n Address of a : %d ", &a);
printf("\n ptr1 : %d ", ptr1);
printf("\n ptr1 : %d ", ptr1);
printf("\n ptr2 : %d ", ptr2);
printf("\n *ptr2 : %d ", *ptr2);
printf("\n **ptr2 : %d ", **ptr2);

Output :
a : 10
Address of a : 4456124
ptr1 : 4456124
*ptr1 : 10
ptr2 : 4456112
*ptr2 : 4456124
**ptr2 : 10

1. int ** const ptr2; Read : ptr2 is a const pointer to pointer to int Ex: int a = 10; int * ptr1 = &a; int ** const ptr2 = &ptr1;

printf("\n a : %d ", a);
printf("\n Address of a : %d ", &a);
printf("\n ptr1 : %d ", ptr1);
printf("\n ptr1 : %d ", ptr1);
printf("\n ptr2 : %d ", ptr2);
printf("\n *ptr2 : %d ", *ptr2);
printf("\n **ptr2 : %d ", **ptr2);

Output :
a : 10
Address of a : 4456124
ptr1 : 4456124
*ptr1 : 10
ptr2 : 4456112
*ptr2 : 4456124
**ptr2 : 10

1. const int ** const ptr2; Read : ptr2 is a const pointer to pointer to const int Ex: const int a = 10; int * ptr1 = &a; const int ** const ptr2 = &ptr1;

printf("\n a : %d ", a);
printf("\n Address of a : %d ", &a);
printf("\n ptr1 : %d ", ptr1);
printf("\n ptr1 : %d ", ptr1);
printf("\n ptr2 : %d ", ptr2);
printf("\n *ptr2 : %d ", *ptr2);
printf("\n **ptr2 : %d ", **ptr2);

Output :
a : 10
Address of a : 4456124
ptr1 : 4456124
*ptr1 : 10
ptr2 : 4456112
*ptr2 : 4456124
**ptr2 : 10

1. int * const * const ptr2; Read : ptr2 is a const pointer to const pointer to int Ex: int a = 10; const int * ptr1 = &a; int * const * const ptr2 = &ptr1;

printf("\n a : %d ", a);
printf("\n Address of a : %d ", &a);
printf("\n ptr1 : %d ", ptr1);
printf("\n ptr1 : %d ", ptr1);
printf("\n ptr2 : %d ", ptr2);
printf("\n *ptr2 : %d ", *ptr2);
printf("\n **ptr2 : %d ", **ptr2);

Output :
a : 10
Address of a : 4456124
ptr1 : 4456124
*ptr1 : 10
ptr2 : 4456112
*ptr2 : 4456124
**ptr2 : 10

1. const int * const * const ptr2; Read : ptr2 is a const pointer to const pointer to const int Ex : const int a = 10; const int * ptr1 = &a; const int * const * const ptr2 = &ptr1;

printf("\n a : %d ", a);
printf("\n Address of a : %d ", &a);
printf("\n ptr1 : %d ", ptr1);
printf("\n ptr1 : %d ", ptr1);
printf("\n ptr2 : %d ", ptr2);
printf("\n *ptr2 : %d ", *ptr2);
printf("\n **ptr2 : %d ", **ptr2);

Output :
a : 10
Address of a : 4456124
ptr1 : 4456124
*ptr1 : 10
ptr2 : 4456112
*ptr2 : 4456124
**ptr2 : 10

Pointer Arithmatic :

1. // i is a integer constant which contains value 10 const int i=10;

// ptr is a pointer to integer constant
const int *ptr = &i;

(*ptr)++;//error
Because trying to modify value of i but i is a const variable.

ptr++;//allowed
Here we incrementing address pointer by ptr by 1. Means suppose address of a is 100.
Now ptr contains 100(address of i)
ptr++ just incrementing 100 to 104. Now if we print value at address 104 ,
it will be print some garbage value.

1. // arr is an array of six integers out of which three are initialized int arr[6]={1,2,3}; // ptr is a pointer to integer which pointing at base address of array arr int *ptr = arr; ptr++;//allowed (*ptr)++;//allowed

Ex:
int arr[6] = {11,22,33};
int *ptr = arr;
printf("\n *ptr : %d ", *ptr);
ptr++;
printf("\n *ptr : %d ", *ptr);
(*ptr)++;
printf("\n *ptr : %d ", *ptr);

Output:
*ptr : 11
*ptr : 22
*ptr : 23

3.// arr is an array of three integer constant
int const arr[3]={1,2,3};

// ptr1 is a pointer to integer which pointing at base address of array arr
int *ptr1 = arr;
ptr1++;//allowed
(*ptr1)++;//allowed
(arr[2])++;//error

Ex:
int arr[] = {12,33,50};
int *ptr1 = arr;
int i = 0;

for (i = 0; i < 3; i++)
{
printf("\nArr[%d] : %d", i,arr[i]);
}

printf("\n ptr1 : %d ", *ptr1);
ptr1++;
printf("\n *ptr1 : %d ", ptr1);
arr[1]++;
printf("\n arr[1] : %d ",arr[1]);

Output:
Arr[0] : 12
Arr[1] : 33
Arr[2] : 50

*ptr1 : 12
*ptr1 : 33
arr[1] : 34