POINTERS

What is a pointer?

1. A pointer is essentially a simple integer variable which holds a memory address that points to a value, instead of holding the actual value itself.
2. The computer’s memory is a sequential store of data,
3. a pointer points to a specific part of the memory.
4. Our program can use pointers in such a way that the pointers point to a large amount of memory - depending on how much we decide to read from that point on.

ROLE OF POINTERS

1. They are used for several reasons, such as:
   • Strings
   • Dynamic memory allocation
   • Sending function arguments by reference
   • Building complicated data structures
   • Pointing to functions
   • Building special data structures (i.e. Tree, Tries, etc…)

Dereferencing / Indirection

1. Dereferencing is the act of referring to where the pointer points, instead of the memory address.
2. We are already using dereferencing in arrays - but we just didn’t know it yet.
3. The brackets operator - [0] for example, accesses the first item of the array.
4. since arrays are actually pointers, accessing the first item in the array is the same as dereferencing a pointer.
5. Dereferencing a pointer is done using the asterisk operator *

/* define a local variable a */
int a = 1;
 
/* define a pointer variable, and point it to a using the & operator */
int * pointer_to_a = &a;
 
printf("The value a is %d\n", a);
printf("The value of a is also %d\n", *pointer_to_a);

6.  we used the & operator to point at the variable a
7. ’&’ is the direction/referencing operator
8. We can also change the contents of the dereferenced variable:

int a = 1;
int * pointer_to_a = &a;
 
/* let's change the variable a */
a += 1;
 
/* we just changed the variable again! */
*pointer_to_a += 1;
 
/* will print out 3 */
printf("The value of a is now %d\n", a);