Re: Trouble with loop in Ada

[Paul Colin Gloster <Colin_Paul_Gloster@ACM.org>]

On 2013-01-04, Derek Wyss <udot7@yahoo.com> sent:
|--------------------------------------------------------------------------|
|"Hello,                                                                   |
|                                                                          |
|I'm new to Ada"                                                           |
|--------------------------------------------------------------------------|

Welcome.

|--------------------------------------------------------------------------|
|" and I'm trying to write a toy unix command shell just to                |
|explore the programming language.  So far I have a very small program,    |
|but I am confused about its behavior.                                     |
|                                                                          |
|If I comment line number 11, with the Put procedure, the program loops    |
|through as I would expect.  However, with that line in the program, I     |
|have to manually press enter twice before I enter the loop.  Similarly, I |
|have to hit enter one more time after the character I enter is displayed  |
|in order for the program to loop again.                                   |
|                                                                          |
|Can anyone offer an explanation as to why I need to press enter?"         |
|--------------------------------------------------------------------------|

Whether or not that line was commented out did not affect how many
times I pressed enter.

|--------------------------------------------------------------------------|
|"  I                                                                      |
|suspect it has to do with my use of End_Of_File and the way it "looks     |
|ahead" but I'm not really sure.                                           |
|                                                                          |
|I'm running Linux Mint Debian Edition with the 3.2.0-4-686-pae kernel.    |
|I'm also using gnat, the Gnu Ada Compiler, version 4.6.  When I compile,  |
|I type at the command prompt:                                             |
|                                                                          |
|gnatmake -gnato -fstack-check -gnatE toy_shell.adb                        |
|                                                                          |
|1  with Ada.Text_IO;                                                      |
|2  use Ada.Text_IO;                                                       |
|3                                                                         |
|4  procedure toy_shell is                                                 |
|5                                                                         |
|6    input_char: Character;                                               |
|7                                                                         |
|8  begin                                                                  |
|9                                                                         |
|10   while not (End_Of_File) loop                                         |
|11     Put("Enter a character> ");                                        |
|12     Get(input_char);                                                   |
|13     Put("you entered: " & input_char);                                 |
|14     New_line;                                                          |
|15   end loop;                                                            |
|16                                                                        |
|17 end toy_shell;                                                         |
|                                                                          |
|I hope that is enough info.  Any help would be greatly appreciated        |
|                                                                          |
|Thanks,                                                                   |
|                                                                          |
|Derek"                                                                    |
|--------------------------------------------------------------------------|


Maybe what you want is . . .

  with Ada.Text_IO;
  use Ada.Text_IO;

  procedure Adapted_Toy_Shell is

     input_char: Character;

  begin

   loop
     Put_Line("Enter a character> ");
     exit when End_Of_File(Standard_Input);
     Get(input_char);
     Put("you entered: " & input_char);
     New_line;
   end loop;

 end Adapted_Toy_Shell;

Maybe instead what you want is:

with Ada.Text_IO;
use Ada.Text_IO;

procedure Adapted_Toy_Shell is

   input_char: Character;

begin
   Loop
      Put_Line("Enter a character> ");
      begin
         Get_Immediate(input_char);
      exception
         when End_Error =>
            exit;
      end;
      Put("you entered: " & input_char);
      New_line;
   end loop;
end Adapted_Toy_Shell;