must be a valid C data type including char, w_char, int, float, double,
bool, or any user-defined object; and
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;
int i, j, k;
declares and defines the variables i, j and k; which instruct
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 are undefined.
Variable Declaration in C
A variable declaration provides assurance to the compiler that there exists a
variable with the given type and name so that the compiler can proceed for
further compilation without requiring the complete detail about the variable. A
variable declaration has its meaning at the time of compilation only, the
compiler needs actual variable declaration at the time of linking 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 the
program. You will use
to declare a variable at any place.
Though you can declare a variable multiple times in your C program, it can be
defined only once in a file, a function, or a block of code.
Try the following example, where variables have been declared at the top, but
they have been defined and initialized inside the main function: