Auto Storage class variables are created each time a function executes and disappear when the function terminates. In other words, the duration of an automatic variable is the duration of the function in which it is declared ad the scope is the function's code. It can be accessed only in that function. Local variables are by default classified as auto variables, because they are allocated automatically when a function is executed and deallocated automatically when the function terminates. Hence, automatic variables cannot retain their values over a number of function calls to that function.
To declare a local variable as automatic, the keyword auto is placed at the head of the declaration:-
auto int i_value;
Since auto is the default storage class for local variables, this keyword is usually omitted. It should also be noted that global variables cannot be declared as auto.