Bronze Edition Guide - True BASIC

106 BRONZE Edition Guide
You’re now using two parameters in the SUB statement above. Sum_dice represents the
sum of the rolls, and num_dice gives the number of dice rolled. The subroutine doesn’t
change num_dice but it does change sum_dice.
To use this new subroutine, you must also use two arguments in the CALL statement. For
example:
CALL Rolldice (dice, 2)
The first argument, dice, is the main program’s name for the sum of dice rolls, and 2 is the
number of dice to be thrown.
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x Arguments share values with their corresponding parameters when the
subroutine runs.
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Dice and sum_dice temporarily become equivalent so that when True BASIC returns to the
main program dice has the value of sum_dice. Similarly, num_dice has the value of 2 during
this call to the subroutine.
This subroutine illustrates two kinds of parameters:
• Num_dice is an input parameter that is only for sending information into a subroutine.
Since an input parameter returns nothing, you may use constants for the corresponding
argument on CALL statements as in the example above.
• Output parameters are variables whose values are changed by the subroutine. They
send information out from the subroutine to the corresponding argument in the main part
of the program. Sum_dice is an output parameter.
• True BASIC does not distinguish between input and output parameters; it's only in the
way you use them.
Built-in Functions
You’ve already seen several of True BASIC’s built-in functions: RND, INT, SQR, and
LCASE$, for example. Appendix C lists most of True BASIC’s built-in functions.
To use a built-in function, all you do is refer to the function by name (perhaps giving it some
information such as the number whose square root you want). True BASIC then “returns”
a value to the program (such as the square root of the number you used with the function.)