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Newsgroups: comp.lang.ada
Date: Mon, 21 May 2018 08:23:20 -0700 (PDT)
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Subject: Should exceeding the range of Integer wrap around a la C?
From: nrs5134@gmail.com
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Xref: reader02.eternal-september.org comp.lang.ada:52543
Date: 2018-05-21T08:23:20-07:00
List-Id: <comp.lang.ada>

Hi all,

I'm brand-new to Ada coming from a Fortran & Python background - just starting to write some trivial tutorial programs. I'm trying to understand the output of following program (copied from the "Lovelace" Ada95 tutorial):

-- compute.adb
-- Demonstrate a trivial procedure, with another nested inside.
with Ada.Text_IO, Ada.Integer_Text_IO;
use Ada.Text_IO, Ada.Integer_Text_IO;

procedure Compute is
   
   procedure Double(Item : in out Integer) is
   begin -- procedure Double
      Item := Item * 2;
   end Double;
   
   X : Integer := 1; -- Local variable X of type Integer
   
begin -- procedure Compute
   loop 
      Put(X);
      New_Line;
      Double(X);
   end loop;
end Compute;

I expect this program to print powers of 2 until `X` exceeds the range of Integer. Instead, it seems to "wrap around" with the following (abbreviated) output:
          1
          2
          4
      [...]          
  268435456
  536870912
 1073741824
-2147483648
          0
          0
      [...]
          0

I am compiling with GNAT 4.9.2 on a Debian Linux system using `gnat make compute` with no further compiler flags. Are my expectations wrong, or is this incorrect behavior?

Cheers,
NS