In Cobol, to test “null or empty” we use “NOT = SPACE [ AND/OR ] LOW-VALUE” ? Which is it?

Question

I am now working in mainframe, in some modules, to test

Not null or Empty

we see : NOT = SPACE OR LOW-VALUE The chief

Answer 1

Chief is correct.

COBOL is supposed to read something like natural language (this turns out to be just another bad joke).

Lets play with the following variables and values:

 A = 1
 B = 2
 C = 3

An expression such as:

IF A NOT EQUAL B THEN...

Is fairly straight forward to understand. One is not equal to two so we will do whatever follows the THEN. However,

IF A NOT EQUAL B AND A NOT EQUAL C THEN...

Is a whole lot harder to follow. Again one is not equal to two AND one is not equal to three so we will do whatever follows the 'THEN'.

COBOL has a short hand construct that IMHO should never be used. It confuses just about everyone (including me from time to time). Short hand expressions let you reduce the above to:

IF A NOT EQUAL B AND C THEN...

or if you would like to apply De Morgans rule:

IF NOT (A EQUAL B OR C) THEN...  

My advice to you is avoid NOT in exprssions and NEVER use COBOL short hand expressions.

What you really want is:

 IF X = SPACE OR X = LOW-VALUE THEN...
    CONTINUE
 ELSE
    do whatever...
 END-IF

The above does nothing when the 'X' contains either spaces or low-values (nulls). It is exactly the same as:

 IF NOT (X = SPACE OR X = LOW-VALUE) THEN
    do whatever...
 END-IF

Which can be transformed into:

 IF X NOT = SPACE AND X NOT = LOW-VALUE THEN...

And finally...

 IF X NOT = SPACE AND LOW-VALUE THEN...

My advice is to stick to simple to understand longer and straight forward expressions in COBOL, forget the short hand crap.