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subroutine subroutine_name ( variable_list )
(tab)statement(s)
end subroutine

Create a subroutine (or subprogram) that will receive zero or more values and process those values. A subroutine does not return a value back to the user, it just does what you want it to do. Execution of a subroutine will terminate and control will be returned to the “calling” program when a Return statement is executed or by allowing the End Subroutine statement to be reached. All variables used within the subroutine, that have not been previously declared as Global, will be local to the subroutine and will not change the values in the calling code.

Subroutine variables may a list of zero or more, comma separated, variables. Arrays and variables may be passed by reference using the Ref definition.

Subroutines should be defined anywhere on your program, but can not be defined within another Function, Subroutine or control block (If/Then, Do/Until, …)

# 100 random circles
clg
for x = 1 to 100
   call draw()
next x
end

function rnd(n)
   rnd = int(rand*n)
end function

subroutine draw()
   color rgb(rnd(256),rnd(256),rnd(256))
   circle rnd(graphwidth), rnd(graphheight), rnd(graphwidth/10)
end subroutine

draws