Wrong Asignment

Wrong Asignment

[Cedric]

Hi All,

I am learning Ada since a few days. In my book is a simple excercise to write a program. It looks like this:

with Text_IO;
with My_Int_IO;
with My_Flt_IO;
----------------------------------------------------------------------
procedure chapter2_programming_projects_1 is
   Celsius    : float := 0.0;
   Fahrenheit : float := 0.0;

begin
   -- Input
   Text_IO.Put("Please put in the temperature in Fahrenheit: ");
   My_Flt_IO.Get(Item => Fahrenheit);
   
   -- Processing
   Celsius := (5/9) x (Fahrenheit - 32);
   
   -- Output
   Text_IO.Put(Item => "The temperature in Celsius is ");
   My_Flt_IO.Put(Item => Celsius, Fore => 10, After => 2);
   
end chapter2_programming_projects_1;

The compiler says:

Celsius := (5/9) x (Fahrenheit - 32); -- binary operator expected

Why does this statement result in an binary object?

Kind regards

Cedric

Re: Wrong Asignment

[Adam Beneschan]

On Friday, May 23, 2014 4:15:26 PM UTC-7, Cedric wrote:
> Hi All,
> 
> 
> 
> I am learning Ada since a few days. In my book is a simple excercise to write a program. It looks like this:
> 
> with Text_IO;
> with My_Int_IO;
> with My_Flt_IO;
> 
> ----------------------------------------------------------------------
> 
> procedure chapter2_programming_projects_1 is
>    Celsius    : float := 0.0;
>    Fahrenheit : float := 0.0;
> 
> begin
>    -- Input
>    Text_IO.Put("Please put in the temperature in Fahrenheit: ");
>    My_Flt_IO.Get(Item => Fahrenheit);  
> 
>    -- Processing
> 
>    Celsius := (5/9) x (Fahrenheit - 32);

The multiplication operator is * (asterisk), not "x".

After you fix this, you will find other errors.  Fahrenheit is a float, and 32 is an integer, and Ada doesn't like it when you mix operand types like that.  You'll need to change the integers in this expression to floats, like this:

     Celsius := (5.0/9.0) * (Fahrenheit - 32.0);

It's actually a good thing that Ada complains about it, because it prevents some misunderstandings.  It is very common for new programmers learning C or C++ or Java to try

     celsius = (5/9) * (fahrenheit - 32);

and then get on a help forum asking why does it keep outputting 0 for celsius?  (It's because 5 and 9 are integers, so the program does integer division which throws away the remainder.)


> Why does this statement result in an binary object?

The error message said "binary operator", not "binary object".  A binary operator is an operator like * that takes two operands.  It was complaining because it expected a binary operator like *, but you gave it "x" which is an identifier.

                             -- Adam

Re: Wrong Asignment

[Cedric]

Hi Adam,

of course your right. Sometimes am blind.

Many thanks for your help.

Regards

Cedric