A variable is nothing but a name given to a storage area
that our programs can manipulate. Each variable in C has a specific type, which
determines the size and layout of the variable's memory; the range of values
that can be stored within that memory; and the set of operations that can be
applied to the variable.
The name of a variable can be composed of letters, digits,
and the underscore character. It must begin with either a letter or an
underscore. Upper and lowercase letters are distinct because C is
case-sensitive. Based on the basic types explained in previous chapter, there
will be the following basic variable types:
Type
|
Description
|
char
|
Typically a single octet(one byte). This is an integer
type.
|
int
|
The most natural size of integer for the machine.
|
float
|
A single-precision floating point value.
|
double
|
A double-precision floating point value.
|
void
|
Represents the absence of type.
|
C programming language also allows to define various other
types of variables, which we will cover in subsequent chapters like
Enumeration, Pointer, Array, Structure, Union, etc. For this chapter, let us
study only basic variable types.
Variable Definition in C:
A variable definition means to tell the compiler where and
how much to create the storage for the variable. A variable definition
specifies a data type and contains a list of one or more variables of that type
as follows:
type variable_list;
Here, type must be a valid C data type including char, w_char, int,
float, double, bool or any user-defined object, etc., and variable_list may consist of one or more
identifier names separated by commas. Some valid declarations are shown here:
int
i, j, k;
char
c, ch;
float
f, salary;
double d;
The line int i, j, k; both declares and defines the
variables i, j and k; which instructs the compiler to create variables named i,
j and k of type int.
Variables can be initialized (assigned an initial value) in
their declaration. The initializer consists of an equal sign followed by a
constant expression as follows:
type variable_name = value;
Some examples are:
extern int d = 3, f = 5; // declaration of d and f.
int d = 3, f = 5; // definition and initializing d and
f.
byte z = 22; // definition and initializes
z.
char x = 'x'; // the variable x has the value
'x'.
For definition without an initializer: variables with static
storage duration are implicitly initialized with NULL (all bytes have the value
0); the initial value of all other variables is undefined.
Variable Declaration in C:
A variable declaration provides assurance to the compiler
that there is one variable existing with the given type and name so that
compiler proceed for further compilation without needing complete detail about
the variable. A variable declaration has its meaning at the time of compilation
only, compiler needs actual variable declaration at the time of linking of the
program.
A variable declaration is useful when you are using multiple
files and you define your variable in one of the files which will be available
at the time of linking of the program. You will use extern keyword to declare a variable at any place. Though you can
declare a variable multiple times in your C program but it can be defined only
once in a file, a function or a block of code.
Example
Try following example, where variables have been declared at
the top, but they have been defined and initialized inside the main function:
#include <stdio.h>
// Variable declaration:
extern int a, b;
extern int c;
extern float f;
int main ()
{
/* variable definition:
*/
int a, b;
int c;
float f;
/* actual initialization
*/
a = 10;
b = 20;
c = a + b;
printf("value of c
: %d \n", c);
f = 70.0/3.0;
printf("value of f
: %f \n", f);
return 0;
}
When the above code is compiled and executed, it produces
the following result:
value of c : 30
value of f : 23.333334
Same concept applies on function declaration where you
provide a function name at the time of its declaration and its actual
definition can be given anywhere else. For example:
// function declaration
int func();
int main()
{
// function call
int i = func();
}
// function definition
int func()
{
return 0;
}
|Footer Menu |
| Introduction | Basic Syntax | Data Types | Variables | Arrays | Constants and Literals |
| Decision Making | Functions | L values and R values | Loops | Nested if statements | Nested loops |
| Nested Switch Statements | Operators | Pointers | Scope Rules |
| Strings | Storage Classes | Structures | Switch Statement |
|Footer Menu |
| Introduction | Basic Syntax | Data Types | Variables | Arrays | Constants and Literals |
| Decision Making | Functions | L values and R values | Loops | Nested if statements | Nested loops |
| Nested Switch Statements | Operators | Pointers | Scope Rules |
| Strings | Storage Classes | Structures | Switch Statement |
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