Like most programming languages, C is able to use and process named variables and their contents. Variables are simply names used to refer to some location in memory - a location that holds a value with which we are working.
It may help to think of variables as a placeholder for a value. You can think of a variable as being equivalent to its assigned value.
A D V E R T I S E M E N T
Variables in C are memory locations with help of which we can be assigned values and are given names .
To store data in memory for later use,we use variables.
In C, a variable must have to be declared before it can be used.
You can declare Variables at the start of any block of code, but most are found at the start of each function.
Most local variables are destroyed on return from that function and created when the function is called.
A declaration begins with the type, followed by the name of one or more than one variables.
You can name a variable anything you like as long as it includes only letters, numbers or underscores and does not start with a number. It is a good idea to keep your variable names less than 32 characters long to save time on typing them out and for compiler compatibility reasons. Variables must always be declared at the top before any other commands are used. Now let's declare an integer variable called a and a character variable called b.:
int main()
{
int a;
char b;
return 0;
}
C keeps a small set of keywords for its own use only.These keywords are given below:
auto
break
case
char
const
continue
default
do
double
else
enum
extern
float
for
goto
if
int
long
register
return
short
signed
sizeof
static
struct
switch
typedef
union
unsigned
void
volatile
while
Identifiers in C
Identifiers" or "symbols" are the names you supply for variables, types,labels, and functions in your program.
Identifier names must differ in case and spelling from any keywords.
You cannot use keywords as the identifiers; they are reserved for special use only. You create an identifier by specifying it in the declaration of a variable,function,or type.
In this example which is given below result is an identifier for an integer variable, and printf and main are identifier names for functions.
Identifiers provide names for the given language elements:
Functions
Function parameters
Macros and macro parameters
Type definitions
Objects
Labels
Enumerated types and enumerators
Structure and union names
#include <stdio.h>
int main()
{
int result;
if ( result != 0 )
printf_s( "Bad file handle\n" );
}
Variable declarations
Variables are of three different types which are as follows:
Global Variable
Local Variable
Static Variable
Global Variable:
The C programming language has an extensive system for declaring variables of different types. The rules for the more complex types can be confusing at times, due to the decisions taken over their design. The principal decision is that the declaration of a variable should be similar, syntactically, to its use (declaration reflects use) .
Declare it outside of all the functions if you want to declare a global variable.
The function will use the variable that was declared within it and ignore the global one,if a variable of the same name is declared both within a function and outside of it.
Local Variable:
Inside the specific function that creates them,these variables only exist.
They are unknown to to the main program and to the other functions.
In this case,they are normally implemented using a stack.
Local variables cease to exist once if the function that created them is completed.
Each time a function is executed or called,they are recreated.
Variable declarations show up in three places:
Outside a function. These declarations declare
global variables which are visible throughout the
program (i.e. they have global scope). Use of
global variables is always a big mistake.
In the header of a function in the argument list .
These variables are the parameters to the function.
They are only visible inside the function body and their local scope),
exist only from when the function is called to when the function
returns (bounded extent---note that this is
different from what happens in some garbage-collected languages like
Scheme), and get their initial values from the arguments to the
function when it is called.
At the start of any block delimited by curly
braces only. Such variables are exist only when the containing function is active
(bounded extent) and visible only within the block (local
scope again). The convention in C is generally to declare all
such local variables at the top of a function; this
is different from the convention in C++ or Java, which encourage
variables to be declared when they are first time used
The following program demonstrate the use of global and local variables.
#include <stdio.h>
int counter = 0; /* global because we are outside all blocks.*/
int func(void);
main()
{
counter++; /* global because it has not been declared within this block */
printf("counter is %2d before the call to func\n", counter);
func(); /* call a function. */
printf("counter is %2d after the call to func\n", counter);
}
int func(void)
{
int counter = 10; /* local variable because it has declared within this block */ */
printf("counter is %2d within func\n", counter);
}
Using static variables
Another important feature of the variable scoping is the static variable.
In a local function scope,a static variable exists only , but it does not lose its value when program execution leaves this scope.
Consider the example which is given below:
#include <stdio.h>
main()
{
Test();
}
function Test()
{
int a = 0;
printf("a is %d within func\n", a)
a++;
}
Since every time the function is called it sets a to 0 and prints "0",this function is quite useless .
The a++ which increments the variable serves no purpose since as soon as the function exits then a variable disappears.
The a variable is declared static to make a useful counting function which will not lose track of the current count:
#include <stdio.h>
main()
{
Test();
}
function Test()
{
static int a = 0;
printf("a is %d within func\n", a)
a++;
}
Basic types
There are 4 basic types of variable in C; they are: char, int, double and float
Type name
Meaning
char
The most basic unit addressable by the machine; typically a
single octet. This is an integral type.
int
The most natural size of integer for the machine; typically
a whole 16, 32 or 64 bit addressable word.
