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From: gaertner@tertius.in-berlin.de
Newsgroups: comp.lang.pascal
Subject: Re: passing two variables
Message-ID: <1991Jun24.175745.6594@tertius.in-berlin.de>
Date: 24 Jun 91 17:57:44 GMT
References: <1991Jun21.144356.19598@javelin.sim.es.com> <1991Jun21.175817.339@maytag.waterloo.edu>
Lines: 46

In article <1991Jun21.175817.339@maytag.waterloo.edu>, dmurdoch@watstat.waterloo.edu (Duncan Murdoch) writes:
> In article <1991Jun21.144356.19598@javelin.sim.es.com> tpehrson@javelin.sim.es.com writes:
>>i would like a function to pass back two variables.  is this possible?  
>>below is an example of what i'd like to accomplish:
>>
>>cx,cy :=checkvalid(cx+offset,cy+offset);
> 
> Not in Turbo or Standard Pascal.  The easiest way to do it is to add variables
> to receive the results as var parameters, which your function (or it could
> be a procedure) can modify.  You have to be a little careful of aliasing,
> e.g. a declaration
> 
>   procedure checkvalid(var in1,in2:integer;var out1,out2:integer);
> 
> would likely get messed up on the call
> 
>   checkvalid(cx,cy,cx,cy);
> 
> since in1 and out1 would both refer to cx, and in2 and out2 would both refer to
> cy.  Passing the input parameters by value (not using var) should work.
> 
> Duncan Murdoch

A clearer solution would be

  PROCEDURE checkvalid ( offset1, offset2 : INTEGER ; { pure input }
                         VAR inout1, inout2 : INTEGER { input/output} ) ;

with the call

  checkvalid ( offset1, offset2, cx, cy ) ;

Refering to the original question:
   Pascal exspects a variable on the left side of an assigment, so there
   will never be a construct like
      x,y := expression ;
In Algol 60 (and I think in C) it is possible to have a list of variables
on the left side of an expression, but note that these variables would get
the same value and not different values.

Ralf

--

  Ralf Gaertner              gaertner@venus.rz-berlin.mpg.de
  FHI Berlin