Bronze Edition Guide - True BASIC

14. Functions and Subroutines 107
In the following short example, answer acquires the value 3.1622777, which is returned by
the function SQR.
LET answer = Sqr(10)
PRINT answer
END
You can think of a function as a machine that takes some numbers or strings as input, and
produces one number or string as output. Functions differ from subroutines in that
• functions can return only one value and
• functions cannot change the values of any parameters sent to them.
Now you’ll see how to define your own functions and use them to break your programs into
logical units.
One-line Functions
One-line functions are the simplest kind of function. You can simulate the rolling of one die
as a one-line function. Here’s the CRAPS program again, rewritten to use a function Rolldie.
! Craps game with one-line function for rolling one die.
!
RANDOMIZE
DEF Rolldie = Int(6*Rnd + 1)
FOR game = 1 to 10
! Roll 1 die
! Play 10 games
LET dice = Rolldie + Rolldie ! Rolldie function twice
SELECT CASE dice
! Branch on roll
CASE 2, 3, 12 ! dice = 2, 3, or 12
PRINT “You lose.”
CASE 7, 11 ! dice = 7 or 11
PRINT “You win.”
CASE ELSE
! Anything else
LET POINT = dice
! Remember that roll
DO
LET dice = Rolldie + Rolldie ! Roll again
LOOP until dice = 7 or dice = point
IF dice=point then PRINT “You win” else PRINT “You lose”
END SELECT
NEXT game
END