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Date: Thu, 22 Nov 2007 08:38:37 +0100
From: Damien Carbonne <damien.carbonne@free.fr>
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To: DarthBob88 <darthbob88@gmail.com>
Subject: Re: "Constraint Error: Range Check" That Does Not Always Occur
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Date: 2007-11-22T08:38:38+01:00
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DarthBob88 a �crit :
> I've been trying to write a program that creates four random numbers,
> to simulate four dice rolling; a D&D simulator, in fact.
> Unfortunately, I occasionally get "raised CONSTRAINT_ERROR : test.adb:
> 22 range check failed" (line 22 is one of the lines to generate a
> random number; it varies between the four). I have been trying to find
> information on how to prevent this error, but I can't find anything
> about it. I'm extremely new to this language, as in I only started
> last week new, so any help would be greatly appreciated. Here follows
> my code, warts and all.
> 
> with Ada.Text_IO, Ada.Integer_Text_IO;
> with Ada.Numerics.Discrete_Random;
> 
> procedure test is
> 	subtype Die is Integer range 1..6;
> 	--Declare that anything of type Die may be
> 	--an integer, value between 1 and 6, inclusive, and sod-all else.
> 	subtype Dice is Integer range 3*Die'First .. 3*Die'Last;
> 	--Declares that Dice may be anything from 3 to 18.
> 	package Random_Die is new Ada.Numerics.Discrete_Random (Die);
Here you instantiate Discrete_Random with Die.
Change Die to Dice, it should work.
> 	use Random_Die;
> 	--Random generator; produces an integer between 1 and 6
> 	sum : Integer := 0;
> 	G: Generator;
>      	D1 : Dice;
> 	D2 : Dice;
> 	D3 : Dice;
> 	D4 : Dice;
> 	--Declare four Dice
> begin
> 	Reset(G);
> 	D1 := Random(G);
> 	D2 := Random(G);
> 	D3 := Random(G);
> 	D4 := Random(G);
Here, Random should have been instantiated with Dice.
> 	--I Haven't found the error just yet, but a Constraint_Error
> 	--Occasionally comes up for the previous 4 lines
> 	--I haven't been able to find it online, but I presume
> 	--It's because the generator comes up with a number outside of [1,6]
> 	sum := D1 + D2 + D3 + D4;
> 	--Debugging
> 	Ada.Integer_Text_IO.Put(D1);
> 	Ada.Integer_Text_IO.Put(D2);
> 	Ada.Integer_Text_IO.Put(D3);
> 	Ada.Integer_Text_IO.Put(D4);
> 	Ada.Integer_Text_IO.Put(sum);
> end test;
> --compile Ada programs with gnat make <foo>.adb
> 
> If it helps any, I'm using the Windows version of GNAT on XP. Thanks
> in advance.