Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!uflorida!haven!adm!xadmx!Brantly.WBST129@xerox.com
From: Brantly.WBST129@xerox.com
Newsgroups: comp.lang.pascal
Subject: Re: Funny evaluation of functions
Message-ID: <20715@adm.BRL.MIL>
Date: 28 Aug 89 11:57:09 GMT
Sender: news@adm.BRL.MIL
Lines: 44


Just to add on to Tom Wiencho's excellent response:

Re: "This is, of course, the difference between passing values by reference
(var) 
and passing them by value.  You generally do not want to pass by
reference if you plan on monkeying with the passed variables unless you 
want the side effects."

RE: ">>
>>   The following code produces 25 as output in Turbo Pascal 4.0.  Can
>>anyone explain what is going on?
>> 
>>  var y:integer;
>>
>>  Function one(var x:integer):integer;
>>  begin
>>   x:=x+1;
>>   one:=x;
>>  end;
>> begin
>>  y:=4;
>>  writeln(output,y*one(y));
>> end.

------

On pg. 67 of the Turbo Pascal User's Guide (5.0) it is stated:

"The keyword VAR in front of X and Y in GetData's procedure statement (as
shown on pg 66) says that the actual paramenters must be variables and that
the variable values can be changed and passed back to the caller."

In other words by using VAR you're explicitly telling the compiler that it
can do this [change the value of your variable]. This is NOT a weakness in
the Turbo compiler, but built-in flexibility for use by the programmer [
and ya know how programmers are, give us enough rope and we'll create a
bug! ]

Dennis

R&D  -Team Xerox-
Joseph C. Wilson Center for Technology
Webster, NY