Campbell CR800 Series, Operator'S Manual

Page: 308 / 598

Section 7. Installation
308
CRBasic example Subroutine with Global and Local Variables
(p. 308)
shows the
use of global and local variables. Variables counter() and pi_product are global.
Variable i_sub is global but used exclusively by subroutine process . Variables
j() and
OutVar
are local since they are declared as parameters in the Sub()
instruction,
Sub process(j(4) AS Long,OutVar).
Variable j() is a four-element array and variable OutVar is a single-element
array. The call statement,
Call ProcessSub (counter(1),pi_product)
passes five values into the subroutine:
pi_product
and four elements of array
counter() . Array counter() is used to pass values into, and extract values from,
the subroutine. The variable pi_product is used to extract a value from the
subroutine.
Call()
passes the values of all listed variables into the subroutine. Values are
passed back to the main scan at the end of the subroutine.
Subroutine with Global and Local Variables
'This program example demonstrates the use of global and local variables with subroutines.
'
'Global variables are those declared anywhere in the program as Public or Dim.
'Local variables are those declared in the Sub() instruction.
'Program Function: Passes two variables to a subroutine. The subroutine increments each
'variable once per second, multiplies each by pi, then passes results back to the main
'program for storage in a data table.
'Global variables (Used only outside subroutine by choice)
'Declare Counter in the Main Scan.
Public counter(2) As Long
'Declare Product of PI * counter(2).
Public pi_product(2) As Float
'Global variable (Used only in subroutine by choice)
'For / Next incrementor used in the subroutine.
Public i_sub As Long
'Declare Data Table
DataTable (pi_results,True,-1)
Sample (1,counter(),IEEE4)
EndTable
'Declare Subroutine
'Declares j(4) as local array (can only be used in subroutine)
Sub ProcessSub (j(2) As Long,OutVar(2) As Float)
For i_sub = 1 To 2
j(i_sub) = j(i_sub) + 1
'Processing to show functionality
OutVar(i_sub) = j(i_sub) * 4 * ATN(1) '(Tip: 4 * ATN(1) = pi to IEEE4 precision)
Next i_sub
EndSub