Pointer variables store memory addresses of other variables. A pointer variable contains the address of the memory location where another variable is stored. Pointers allow access and modification of the variable being pointed to using dereferencing operator (*). Arrays can also be treated as pointers, as the name of an array represents the address of its first element. Pointers provide benefits like dynamic memory allocation, passing arguments by reference, and building complex data structures.

1. Pointers
9/11/2017 1MRI

2.  Each variable is assigned a memory slot (the
size depends on the data type) and the
variable’s data is stored there
Variable a’s value, i.e., 100, is
stored at memory location 1024
100… … 1024 …
Memory address: 1024 1032
int a = 100;
…
1020
a
9/11/2017 2MRI

3.  A pointer is a variable used to store the
address of a memory cell.
 We can use the pointer to reference this
memory cell
100… … 1024 …
Memory address: 1024 1032
…
1020
integer
pointer
9/11/2017 3MRI

4. 4
 Pointer stores the address of another entity
 It refers to a memory location
int i = 5;
int *ptr; /* declare a pointer variable */
ptr = &i; /* store address-of i to ptr */
printf(“*ptr = %dn”, *ptr); /* refer to referee of ptr */
9/11/2017 MRI

5. 5
 ptr is a variable storing an address
 ptr is NOT storing the actual value of i
int i = 5;
int *ptr;
ptr = &i;
printf(“i = %dn”, i);
printf(“*ptr = %dn”, *ptr);
printf(“ptr = %pn”, ptr);
5i
address of iptr
Output:
i = 5
*ptr = 5
ptr =
effff5e0
value of
ptr =
address of i
in memory
9/11/2017 MRI

6. Pointer has the following advantages :-
Using pointers we can allocate memory dynamically to
structures (Dynamic memory allocation).
Arrays or strings can be passed to function more
efficiently.
Better memory management or our program will run
faster.
Pointer helps us to build complex data structures like
linked lists, trees etc.
Provides alternate way to access array elements of any
dimension.
Used to return more than one value from function.
Pointers can increase the execution speed of program.9/11/2017 6MRI

7.  Declaration of Pointer variables
data_type *pointer_name;
where
1. Data_type is the type of data pointed to (e.g. int,
char, double)
2. The asterisk (*) tells the variable is a pointer variable
3. Pointer_name needs a memory location
Examples:
int *n;
RationalNumber *r;
int **p; // pointer to pointer

9/11/2017 7MRI

8. 9/11/2017 8MRI
Once a pointer variable has been declared we
can use the assignment operator to intialize the
varibale.
Example:
int quantity;
int *p;
p=&quantity;

9.  The "address of " operator (&) gives the memory
address of the variable
 Usage: &variable_name
 The address (&) operator can be used in front of
any variable object in C -- the result of the
operation is the location in memory of the
variable
100… … … …
Memory address: 1024
…
1020
a
9/11/2017 9MRI

10. A pointer can also be made to point to a pointer
variable (but the pointer must be of a type that
allows it to point to a pointer)
Example:
intV = 101;
int *P = &V; /* P points to intV */
int **Q = &P; /* Q points to int pointer P */
9/11/2017 10MRI

11. Pointers are generally of the same size (enough bytes
to represent all possible memory addresses), but it
is inappropriate to assign an address of one type of
variable to a different type of pointer
Example:
intV = 101;
float *P = &V; /* Generally results in aWarning */
Warning rather than error because C will allow you to
do this (it is appropriate in certain situations)
9/11/2017 11MRI

12. When assigning a memory address of a variable of one
type to a pointer that points to another type it is
best to use the cast operator to indicate the cast is
intentional (this will remove the warning)
Example:
intV = 101;
float *P = (float *) &V; /* Casts int address to float *
*/
Removes warning, but is still a somewhat unsafe thing
to do
9/11/2017 12MRI

13. A void * is considered to be a general pointer.
No cast is needed to assign an address to a void * or
from a void * to another pointer type.
Example:
intV = 101;
void *G = &V; /* No warning */
float *P = G; /* No warning, still not safe */
Certain library functions return void * results (more
later)
9/11/2017 13MRI

14. int A[5] - A is the address where the array starts (first
element), it is equivalent to &(A[0])
A is in some sense a pointer to an integer variable.
To determine the address of A[x] use formula:
(address ofA + x * bytes to represent int)
(address of array + element num * bytes for element size)
The + operator when applied to a pointer value uses
the formula above:
A + x is equivalent to &(A[x])
*(A + x) is equivalent to A[x]
9/11/2017 14MRI

15. float A[6] =
{1.0,2.0,1.0,0.5,3.0,2.0};
float *theMin = &(A[0]);
float *walker = &(A[1]);
while (walker < &(A[6])) {
if (*walker < *theMin)
theMin = walker;
walker = walker + 1;
}
printf("%.1fn",*theMin);
9/11/2017 15MRI

16. Array of Pointers & Pointers to Array
a
b
c
An array of Pointers
p
int a = 1, b = 2, c = 3;
int *p[5];
p[0] = &a;
p[1] = &b;
p[2] = &c;
int list[5] = {9, 8, 7, 6, 5};
int *p;
P = list;//points to 1st entry
P = &list[0];//points to 1st entry
P = &list[1];//points to 2nd entry
P = list + 1; //points to 2nd entry
A pointer to an array
9/11/2017 16MRI

17.  The name of an array points only to the first
element not the whole array.
1000
1012
1016
1004
1008
9/11/2017 17MRI

18. When passing whole array as parameter use syntax
ParamName[], but can also use *ParamName
Still treat the parameter as representing array:
int totalArray(int *A, int N) {
int total = 0;
for (I = 0; I < N; I++)
total += A[I];
return total;
}
For multi-dimensional arrays we still have to use the
ArrayName[][Dim2][Dim3]etc. form
9/11/2017 18MRI

19.  We can access to the value stored in the variable pointed
to by using the dereferencing operator (*),
10088 … 1024 …
Memory address: 1024 1032
…
1020
int a = 100;
int *p = &a;
 Result is:
100
1024
1024 100
1032
a p
9/11/2017 19MRI

20.  Declaring a pointer means only that it is a pointer: int
*p;
 Don’t be confused with the dereferencing operator, which
is also written with an asterisk (*).They are simply two
different tasks represented with the same sign
int a = 100, b = 88, c = 8;
int *p1 = &a, *p2, *p3 = &c;
p2 = &b; // p2 points to b
p2 = p1; // p2 points to a
b = *p3; //assign c to b
*p2 = *p3; //assign c to a
 Result is:
888
9/11/2017 20MRI