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From the beginning, we only show how to access or change directly the values of variables through their names. However, the C language provides the developers an effective method to access variables - pointer.

A pointer is a variable that contains the address of a variable. Pointers are much used in C, partly because they are sometimes the only way to express a computation, and partly because they usually lead to more compact and efficient code than can be obtained in other ways. Pointers and arrays are closely related; this Unit also explores this relationship and shows how to exploit it.

Pointers and addresses

Let us begin with a simplified picture of how memory is organized. A typical machine has an array of consecutively numbered or addressed memory cells that may be manipulated individually or in contiguous groups. One common situation is that any byte can be a char, a pair of one-byte cells can be treated as a short integer, and four adjacent bytes form a long.

Any variable in a program is stored at a specific area in memory. If you declare a variable, the compiler will allocate this variable to some consecutive memory cells to hold the value of the variable. The address of the variable is the address of the first memory cell.

One variable always has two properties:

  • The address of the variable
  • The value of the variable.

Consider the following Example

int i, j; i = 3;j = i;

Type of these two variables is integer so they are stored in 2-byte memory area. Suppose that the compiler allocates i at the FFEC address in memory and j in FFEE, we have:

Variable Address Value
i FFEC 3
j FFEE 3

Two different variables have different addresses. The i = j assignment affects only on the value of variables, that means the content of the memory area for j will be copied to the content of the memory area for i.

Pointers

A pointer is a group of cells (often two or four) that can hold an address. So if c is a char and p is a pointer that points to it, we could represent the situation this way:

Pointer declaration

If you declare a variable, its name is a direct reference to its value. If you have a pointer to a variable or any other object in memory, you have an indirect reference to its value. A pointer variable stores the address of another object or a function. To start out, the declaration of a pointer to an object that is not an array has the following syntax:

type * Name [= initializer];

In declarations, the asterisk (*) means "pointer to". The identifier name is declared as an object with the type *, or pointer to type. * is the indirection or dereferencing operator; when applied to a pointer, it accesses the object the pointer points to.

Here is a simple Example

int *iPtr; // Declare iPtr as a pointer to int. double *realptr; // pointer to a doublechar *astring; // pointer to a character

The type int is the type of object that the pointer iPtr can point to.

To make a pointer refer to a certain object, assign it the address of the object.

For example, if iVar is an int variable, then the following assignment makes iPtr point to the variable iVar:

Questions & Answers

Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
Praveena Reply
hi
Loga
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
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Source:  OpenStax, Introduction to computer science. OpenStax CNX. Jul 29, 2009 Download for free at http://cnx.org/content/col10776/1.1
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