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KOUSIK · Beginner Joined: 04 Jan 2005 Posts: 26 Topics: 13

Can somebody please help me out in a way to evaluate a passed arithmetic expression in COBOL.

We have a logic wherein we form arithmetic expressions in our shop. But, we need to evaluate these arithmetic expressions to TRUE or FALSE and proceed based on the result to a different logic.

Say for example,

I may form an expression like : (A+B*(C-D)+E) < (F+G-(H+I))

or an expression like

(A-B+(C*D)-E) > (F+G*(H-I)) ,

I will have to evaluate such expressions to a true or false.

Note : The expressions are dynamic. We have logic to form these expressions.

As far I know COBOL can evaluate static expressions to either TRUE or FALSE.

Any help is greatly appreciated!

Regards,
Kousik

CICS Guy · Intermediate Joined: 30 Apr 2007 Posts: 292 Topics: 3

Assuming the program has access to the values of the variables, the evaluation of the expression should be a straight forward programming exersize.....

jyoung · Posted: Thu Nov 08, 2007 1:13 pm Post subject:

Would this work?
compute x = (A+B*(C-D)+E)
compute j = (F+G-(H+I))
if x < j
do something (true)
else
do something else. (false)

CraigG · Posted: Thu Nov 08, 2007 1:41 pm Post subject:

KOUSIK · Beginner Joined: 04 Jan 2005 Posts: 26 Topics: 13

Thanks for the response!

But, jyoung wrote

jsharon1248 · Posted: Thu Nov 08, 2007 2:22 pm Post subject:

As previously stated, it will be very difficult to come up with a solution in COBOL because it is a compiled language. You'd be better off using the right tool for the job. REXX would be a better choice because you could use the INTERPRET command which does exactly what you want; executes a statement generated at execution. You might be able to play around with DB2 and generate dynamic SQL with a CASE, but that's probably more trouble than it's worth.

CICS Guy · Intermediate Joined: 30 Apr 2007 Posts: 292 Topics: 3

KOUSIK · Beginner Joined: 04 Jan 2005 Posts: 26 Topics: 13

Sharon,

Thanks a lot...I definitely learnt a new instruction in REXX...May be I will try using this one and let you know how it works out...

I am not sure if I can couple REXX and COBOL somehow but high time I crack this down...

Really appreciate all you guys for the advise.

semigeezer · Posted: Thu Nov 08, 2007 6:58 pm Post subject:

The normal way to do this is to create a parse tree to represent the tokens and operators in tree form. If I recall, nodes are either operators or variables and the tree is built in a form such that the order of traversal matches the precedence of operators (which when traversed results in so-called "reverse polish notation"). For example, parenthesized operations are a subtree. To do the actual evaluation, you then traverse the tree either doing operations or variable value substitutions. It has been 25+ years since I looked at this type of thing, but I think that is the basic idea. If you want to get details, look in one of the standard compiler texts (like Aho, Sethi & Ullman) or a good algorithm book (presumably Knuth or Tremblay & Sorensen).

The problem with doing this in COBOL is that COBOL stinks when it comes to dynamic data structures. PL/I would be a better choice. For tree representation, you can, of course, use arrays and fake it (Indexes simulate pointers for example), but that is kind of ugly.

I suspect that you could buy commercial callable routines to do this sort of evaluation but I have no experience with that (and I haven't seen such utility packages advertised in a long time).
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jsharon1248 · Posted: Fri Nov 09, 2007 9:09 am Post subject:

KOUSIK

Passing the expression from COBOL to REXX will be a little tricky. You stated that the expression is dynamic. How will you know what variables to pass from the COBOL module to the REXX exec? I'm not saying that it can't be done, just that you'd need to devise a way to do it. If possible, it would be easier to code and maintain if you let REXX do more of the work. In other words, generate and evaluate the expression in REXX.