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From: Simon Clubley <clubley@remove_me.eisner.decus.org-Earth.UFP>
Newsgroups: comp.lang.ada
Subject: Re: actual for variable name must be variable compiler error
Date: Mon, 29 Sep 2014 19:37:40 +0000 (UTC)
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Date: 2014-09-29T19:37:40+00:00
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On 2014-09-29, Brian Drummond <brian3@shapes.demon.co.uk> wrote:
> On Sun, 28 Sep 2014 17:48:20 -0700, Stribor40 wrote:
>
>> procedure myFunction (a: in out INTEGER) is
>>     begin
>         a := 4;
>>     end;
>  
>>    myFunction(5) this gives me error that actual must be variable
>
> is equivalent to
>    
>    5 := 4;
>
> Not bloody likely!
>
> - Brian

The problem may be that in C it's possible to write the following:

#include <stdio.h>

void update_value(unsigned long int a);

int main(int argc, char *argv[])
	{
	update_value(4);
	update_value(6);
	return(0);
	}

void update_value(unsigned long int a)
	{
	printf("Value of a on entry to update_value() is %lu\n", a);
	a = a + 7;
	printf("Value of a after modification is %lu\n", a);
	return;
	}

which when compiled and run gives:

[simon@[deleted] ~]$ gcc -Wall -Werror -o ro_update ro_update.c
[simon@[deleted] ~]$ ./ro_update 
Value of a on entry to update_value() is 4
Value of a after modification is 11
Value of a on entry to update_value() is 6
Value of a after modification is 13
[simon@[deleted] ~]$

Notice how you can modify (at least locally) what in Ada would be an
in parameter and it doesn't matter if an integer constant was passed
as was done in this case.

The OP may be getting confused and thinking you can do the same
with integer constants in Ada.

Simon.

-- 
Simon Clubley, clubley@remove_me.eisner.decus.org-Earth.UFP
Microsoft: Bringing you 1980s technology to a 21st century world