BASIC: What does an exclamation mark at the end of a function name mean? -

declare function aanuit! (baan integer, aktie integer) declare function fvraagstatus! (baan integer) declare function fmelding! (tekst string, warning integer)  function fvraagstatus (vraagbaan integer)   ´ retrieve status somewhere   fvraagstatus = false or true end function  function fmelding (tekst string, warning integer)   ´ locate (move cursor), print stuff end function 

my question: exclamation mark @ end of function name mean?

i rewritting old program .net , came across weird , want understand why there '!' @ end of function decleration. don't need write own code, it's peace of mind.

it means function returns single. exclamation point shortcut as single.