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From: Stuart Palin <stuart.palin@0.0>
Newsgroups: comp.lang.ada
Subject: Re: Simple program to find average of 3 numbers
Date: Fri, 04 Jul 2003 09:37:45 +0100
Organization: Computer Sciences Corporation
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Date: 2003-07-04T09:37:45+01:00
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"Robert I. Eachus" wrote:
> 
> prashna wrote:
>  > Hi friends,
>  >
>  > What is wrong in the following program which is giving constraint
>  > error?
>  >
>  > procedure average is type ONE_TO_100 is range 1 .. 100;
>  >
>  > OBJ1, OBJ2, OBJ3, AVG  : ONE_TO_100; begin OBJ1 := 70; OBJ2 := 70;
>  > OBJ3 := 70; AVG := OBJ1+OBJ2+OBJ3/3; end average;
> 
<snip>
> 
> Oh, and then I could talk about your formatting, and identifier style.
> But I will address those by example.  Try:
> 
> procedure Average is
>    subtype One_to_100 is Integer range 1 .. 100;
>    Obj_1, Obj_2, Obj_3: One_to_100 := 70;
>    Avg: One_to_100;
> begin
>    Avg := (Obj_1+Obj_2+Obj_3)/3;
>    -- I assume you really wanted the average, rather than 163.
> end Average;

You might also want to consider what values the intermediate
calculation Obj_1+Obj_2+Obj_3 can take.  In this instance
because your type is constrained to a number which should be
well within the bounds of integer you would not experience a
problem.

Questions to ask yourself (and seek answers to):
a) What if the bounds of the type were larger?
b) How might it be possible to detect a potential constraint
error at compile time rather than during execution?

--
Stuart Palin