Bronze Edition Guide - True BASIC

108 BRONZE Edition Guide
Once you have defined a function in a DEF statement, you use that function simply by
using its name where you would a variable. True BASIC carries out the instructions in the
DEF statement and the resulting value is “returned” to the function name.
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x You must define a function before you use it in your program.
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If you don’t define it first, True BASIC won’t know that you are referring to a function and
not a variable or array when you use the function name.
Multi-line Functions
You can also write multi-line functions to solve problems that require several lines of True
BASIC statements. DEF and END DEF statements define a multi-line function. As with
one-line functions, you must define your multi-line functions before you use them.
The SGN function is a multi-line function already built into True BASIC. SGN returns the
sign of a number. That is, you give it a single number as an argument, and it returns:
-1 if the number is negative
0 if the number equals 0
+1 if the number is positive
You could easily define a SGN function yourself and test it as follows:
! Define the Sgn function
!
DEF Sgn(x)
SELECT CASE x
CASE is < 0 ! If negative . . .
LET Sgn = -1 ! . . .return -1
CASE 0 ! If zero . . .
LET Sgn = 0 ! . . .return a 0
CASE else
! Otherwise must be positive
LET Sgn = +1 ! . . .return +1
END SELECT
END DEF
INPUT n
PRINT Sgn(n)
PRINT Sgn(3-5*2)
END
! Input a number
! Print its sign
! And the sign of this formula