The C Programming Language - Pointers

As you can see, working with pointers can be a bit confusing. Therefore, here is a brief
summary of how pointers are used:
char ch = 'A';
int a = 0, y = 10;
float z = 0.0, x = 3.14;
int *iptr1 = (int *)0x0061ff14; // typecast to an int* - iptr1 points to 0x0061ff14
int *iptr_a;
// undefined int pointer
int *iptr_y = NULL;
// int pointer initialized to NULL
float *fptr_x;
// undefined float pointer
fptr_x = &x;
char cptr_ch = &ch;
// defined float pointer - fptr_x points to x
// defined float pointer - fptr_x points to x
iptr_y = &y;
// iptr_y stores the address of y
*iptr_y = 1000; // iptr_y points to y -> now y = 1000;
a = *iptr_y; // a stores the value pointed to by iptr_y -> a = 1000
*iptr_y = a + 500; // y = 1000 + 500 -> now y = 1500
iptr_a = &a;
// iptr_a stores the address of a
printf("%d\n" , *iptr_a);
printf("%p\n" , iptr_a);
// displays the value a
// displays the Address of a
1.4 Pointer of Pointers
A pointer to a pointer contains the address of a pointer to which it points. A simple
pointer contains the address of a variable. However, when a pointer points to another
pointer, the first pointer contains the address of the second pointer, which in turn
points to the variable that contains a value.
In the following figure, the pointer pptr points to another pointer ptr, which in turn
points to the variable b. With double dereferencing, you can use the pointer ptr to
access the variable b directly.
Figure 1: Pointer to pointer
The C Programming Language by Heimo Gaicher – Chapter Pointers 14