Language Definition – Subroutines

Subroutines are similar to functions except subroutines have no return value and therefore the identifier name does not have a data type symbol. The general syntax for a subroutine is:

    SUB sub_name(arguments)
   ...
    END SUB

The arguments will be optional. Arguments will be called by reference if a variable or array element is used as an argument, otherwise the arguments are by values. The arguments will be treated as local variables, except if called by reference, modifying the local variable was also modify the caller's variable or array element. The by reference call can be prevented by surrounding the argument in the function call by parentheses as in (A). Entire arrays can be passed by reference by using just the array name in the subroutine call.

Subroutines may call themselves recursively. It is up to the programmer to prevent an infinite loop, though eventually memory will run out as each subroutine call will increase the size of the stack.

The subroutine will return upon a RETURN statement or when the END SUB statement is reached. The SUB will not be executed upon reaching the SUB statement, execution will proceed to the after the END SUB statement. The subroutine will be called using a CALL statement as:

    CALL sub_name(arguments)

Updated Saturday January 2, 2010; 9:45am: Looks like most of the BASICs use just "SUB" for subroutine, so I decided to also use just SUB instead of SUBROUTINE.