Variable Parameter (Pass by Reference) ☆

When a variable is passed to a subprogram, the parameter is made to point to the same location in the memory as that of the argument.
Therefore, if the argument passed to a subprogram is a variable, when the parameter is changed, the argument also changes.

Example.

100  DECLARE EXTERNAL SUB exchange
110  LET a=1
120  LET b=2
130  CALL exchange(a,b)
140  PRINT a,b
150  END
200  EXTERNAL SUB exchange(x,y)
210  LET t=x
220  LET x=y
230  LET y=t
240  END SUB

If you want the argument not to be changed, write it in parenthesis as follows.
130 CALL exchange((a),(b))


Note.
On function definitions, parameters are placed at different location of the arguments. Thus any function definition does not change arguments.