A variable is just a named area of storage that can hold a single value (numeric or
character). The C language demands that you declare the name of each variable that
you are going to use and its type, or class, before you actually try to do anything
The Programming language C has two main variable types
Local variables scope is confined within the block or function where it is
defined. Local variables must always be defined at the top of a block.
When a local variable is defined - it is not initalised by the system, you
must initalise it yourself.
When execution of the block starts the variable is available, and when the
block ends the variable 'dies'.
Check following example's output
if (j > 0)
/* i defined in 'main' can be seen */
printf("i is %d\n",i);
if (j > 0)
/* 'i' is defined and so local to this block */
printf("i is %d\n",i); }/* 'i' (value 100) dies here */
printf("i is %d\n",i); /* 'i' (value 5) is now visable.*/
This will generate following output
i is 5
i is 100
i is 5
Here ++ is called incremental operator and it increase the value of any
integer variable by 1. Thus i++ is equivalent to i = i + 1;
You will see -- operator also which is called decremental operator and it
idecrease the value of any integer variable by 1. Thus i-- is equivalent to
i = i - 1;
Global variable is defined at the top of the program file and it can be visible and
modified by any function that may reference it.
Global variables are initalised automatically by the system when you define them
If same variable name is being used for global and local variable then local variable
takes preference in its scope. But it is not a good practice to use global variables
and local variables with the same name.
int i=4; /* Global definition */
i++; /* Global variable */
printf( "Value of i = %d -- main function\n", i );
int i=10; /* Local definition */
i++; /* Local variable */
printf( "Value of i = %d -- func() function\n", i );
This will produce following result
Value of i = 11 -- func() function
Value of i = 5 -- main function
i in main function is global and will be incremented to 5. i in
func is internal and will be incremented to 11. When control returns to main
the internal variable will die and and any reference to i will be to the
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