I'm an absolute beginner in Ada and I'm trying to calculate sin(x) [sin(3) now] by using Taylor-series, but I just can't get it to work.
So here is my procedure:
with Ada.Float_Text_IO;
with Mat;
procedure SinKoz is
X:Float:=3.0;
Szamlalo:Float:=0.0;
begin
for I in 1..100 loop
Szamlalo := Szamlalo + ((-1.0)**I)*(X**(2.0*I+1.0))/Mat.Faktorialis(2*I+1);
end loop;
Ada.Float_Text_IO.Put( Szamlalo );
end SinKoz;
And inside Mat, here is my Faktorialis, which calculates the factorial of 2*I+1:
function Faktorialis( N: Float ) return Float is
Fakt : Float := 1.0;
begin
for I in 1..N loop
Fakt := Fakt * I;
end loop;
return Fakt;
end Faktorialis;
When i'm trying to compile my code, this error comes up:
exponent must be of type Natural, found type "Standard.Float"
I hope you can help me trying to figure out what went wrong with my types!
The first question is : do you need to raise X to a non-integer power?
It looks to me as if you don't : in which case replace X**(2.0*I+1.0) with X**(2*I+1) and all will be well.
But if you really do (perhaps not here, but in another application) you just need to make such an operator visible : there's one for Float in the package Ada.Numerics.Elementary_Functions so precede your function with
with Ada.Numerics.Elementary_Functions;
use Ada.Numerics.Elementary_Functions;
and it should work as written.
Finally, if you have created your own float type, you can instantiate the generic package Ada.Numerics.Generic_Elementary_Functions with your type as its parameter, to create a set of these functions specifically for your type.
Gotta love Ada's strong typing.
Off the top of my head, I suspect your problem may be this line:
Szamlalo := Szamlalo + ((-1.0)**I)*(X**(2.0*I+1.0))/Mat.Faktorialis(2*I+1);
2.0*I+1.0 is going to return a Float. Not a Natural. You could try wrapping that in Integer() or Natural() (Natural is a subtype of Integer) and see if that helps.
Related
I'm trying to write a code in Spark that computes the value of the polynomial using the Horner method. The variable Result is calculated by Horner, and the variable Z is calculated in the classical way. I've done a lot of different tests and my loop invariant is always true. However, I get the message:
loop invariant might not be preserved by an arbitrary iteration
Are there any cases where the loop invariant doesn't work or do you need to add some more conditions to the invariant?
Here's my main func which call my Horner function:
with Ada.Integer_Text_IO;
use Ada.Integer_Text_IO;
with Poly;
use Poly;
procedure Main is
X : Integer;
A : Vector (0 .. 2);
begin
X := 2;
A := (5, 10, 15);
Put(Horner(X, A));
end Main;
And Horner function:
package body Poly with SPARK_Mode is
function Horner (X : Integer; A : Vector)
return Integer
is
Result : Integer := 0;
Z : Integer := 0;
begin
for i in reverse A'Range loop
pragma Loop_Invariant (Z=Result*(X**(i+1)));
Result := Result*X + A(i);
Z := Z + A(i)*X**(i);
end loop;
pragma Assert (Result = Z);
return Result;
end Horner;
end Poly;
How is Vector defined? Is it something like
type Vector is array(Integer range <>) of Float;
In this case maybe the condition could fail if some indexes of A are negative. Also, does the invariant hold even if the first index of A is not zero? Maybe another case when the invariant fails is when A'Last = Integer'Last; in this case the i+1 would overflow.
Usually SPARK gives a reason, a counterexample, when it is not able to prove something. I would suggest you to check that, it can give you an idea of when the invariant fails. Keep in mind that the counterexamples are sometimes some very extreme case such as A'Last = Integer'Last. If this is the case you need to tell SPARK that A'Last = Integer'Last will never happen, maybe by defining a specific subtype for Vector index or by adding a contract to your function.
I am writing program: sum of real numbers using recursive function.
What is wrong with it? It shows me just last entered numebr.
type
Indexy = 1..100;
TPoleReal = array [Indexy] of Real;
var
j: word;
r, realRes: real;
tpr: TPoleReal;
function SoucetCisel(n: TPoleReal; j: word): real;
begin
if j>0 then begin
SoucetCisel:=SoucetCisel + n[j];
j:=j-1;
end
end;
begin i:=0; j:=0;
while not seekeof do begin
read(r); Inc(j);
tpr[j]:=r;
writeln(j, ' ', tpr[j]);
end;
realRes:= SoucetCisel(tpr, j);
writeln(realRes);
end.
For debugging purposes I suggest you simplify the main part of your code to
begin
i:=0;
j:=0;
tpr[j] := 1;
Inc(j);
tpr[2] := 2;
realRes:= SoucetCisel(tpr, j);
writeln(realRes);
end.
That should make it make it much easier to appreciate what the problem is.
The first problem with your SoucetCisel function is that it isn't actually recursive.
A recursive function is one which calls itself with altered arguments, as in the
archetypical Factorial function
function Factorial(N : Integer)
begin
if N = 1 then
Factorial := 1
else
Factorial := N * Factorial(N - 1);
end;
The recursive call in this is the line
Factorial := Factorial(N - 1);
Your SoucetCisel doesn't do that, it simply adds the initial value of the function result
to the value of n[j], so it is not recursive at all.
The other problem is that, as written, it has no defined return value. In all the
Pascal implementations I've come across, the return value is undefined on entry to the
function and stays undefined until some value is explicitly assigned to it. The
function result is usually some space on the stack which the compiler-generated
code of the function reserves but which initially (on entry to the function) holds some random value, resulting from previous usage of the stack.
So, what the result of your SoucetCisel function is evaluated from is effectively
SoucetCisel := ARandomNumber + n[j]
which of course is just another random number. Obviously, you fix this aspect
of your function by ensuring that an explicit assignment to the function result is made
immediately on entry to the function. As a general rule, all execution paths through a function should lead through a statement which explicitly assigns a
value to the function result.
Then, you need to rewrite the remainder of it so that it actually is recursive
in the way your task requires.
While you're doing those two things, I would suggest that you use a more
helpful parameter name than the anonymous 'n'. 'n' is usually used to refer to an uninteresting integer.
update I'm not sure from your comment whether it was supposed to be serious. In case it was, consider these two functions
function SumOfReals(Reals : TPoleReal; j : word): real;
var
i : Integer;
begin
SumOfReals := 0;
for i := 1 to j do
SumOfReals := SumOfReals + Reals[i];
end;
function SumOfRealsRecursive(Reals : TPoleReal; j : word): real;
var
i : Integer;
begin
SumOfRealsRecursive := Reals[j];
if j > 1 then
SumOfRealsRecursive := SumOfRealsRecursive + SumOfRealsRecursive(Reals, j -1);
end;
These functions both do the same thing, namely evaluate the sum of the contents
of the Reals array up to and including the index j. The first one does so iteratively,
simply traversing the Reals array, which the second does it recursively. However,
it should be obvious that the recursive version is absolutely pointless in this case because
the iterative version does the same thing but far more efficiently, because
it does not involve copying the entire Reals array for each recursive call, which the recursive version does.
As I told you in a comment before. Try this code for your pascal program:
type
Indexy = 1..100;
TPoleReal = array [Indexy] of Real;
var
j: word;
r, realRes: real;
tpr: TPoleReal;
function SoucetCisel(n: TPoleReal; j: word): real;
begin
if j>0 then begin
SoucetCisel:=SoucetCisel(n, j-1) + n[j];
end
end;
begin i:=0; j:=0;
while not seekeof do begin
read(r); Inc(j);
tpr[j]:=r;
writeln(j, ' ', tpr[j]);
end;
realRes:= SoucetCisel(tpr, j);
writeln(realRes);
end.
I'm in the process of making my own package for an Ada main program. I read a string followed by an integer and another string and the problem is I need to cut the first string at sign of first space. I don't know how to do it and I've searched stack overflow only to find solutions in other languages.
My code right now in the package body is:
Get_Line(Item.String, Item.X1)
where X1 is an integer and String is the string. This works if you define the length in the type to match the exact length of your input but of course you want to be able to insert whatever you want and thus it doesn't work.
Can somebody point me in the right direction?
Thanks
Why do you need to make a package for an Ada main program? Most compilers need them to be parameterless library-level procedures.
Anyway, this might give you some tips.
with Ada.Text_IO;
with Ada.Integer_Text_IO;
procedure Agrell is
begin
declare
Line : constant String := Ada.Text_IO.Get_Line;
This is how to deal with reading a string of unknown length. You have to work out how to preserve it for future use (maybe use an Unbounded_String?)
The_Integer : Integer;
begin
Looking_For_Space :
for J in Line'Range loop
if Line (J) = ' ' then
Everything from Line’First to J - 1 is the string you wanted.
declare
Dummy : Positive;
begin
Ada.Integer_Text_IO.Get (From => Line (J .. Line'Last),
Item => The_Integer,
Last => Dummy);
end;
OK, now we have The Integer...
...
exit Looking_For_Space;
... and we’re done with the first line.
end if;
end loop Looking_For_Space;
end;
end Agrell;
I am attempting to understand how to fix this circular dependency. All the examples I can find online suggest using a limited with, but then they demonstrate the use with two basic types, whereas this is a bit more advanced. The circular dependency is between the two files below. I thought it was between package Chessboard ... and the Piece type, but now I am not so sure. Attempting to put the package Chessboard ... line within chess_types.ads after the Piece type is declared and removing the use and with of Chessboard results in an error: this primitive operation is declared too late for the Move procedure. I am stuck on how to get out of this dependency. Any help would be much appreciated!
Thank you
chessboard.ads:
with Ada.Containers.Indefinite_Vectors;
use Ada.Containers;
with Chess_Types;
use Chess_Types;
package Chessboard is new Indefinite_Vectors(Board_Index, Piece'Class);
chess_types.ads:
with Ada.Containers.Indefinite_Vectors;
use Ada.Containers;
with Chessboard;
use Chessboard;
package Chess_Types is
subtype Board_Index is Integer range 1 .. 64;
type Color is (Black, White);
type Piece is tagged
record
Name : String (1 .. 3) := " ";
Alive : Boolean := False;
Team : Color;
Coordinate : Integer;
end record;
procedure Move_Piece(Board: in Vector; P: in Piece; Move_To: in Integer);
end Chess_Types;
More Code for question in comments:
Chess_Types.Piece_Types.ads:
package Chess_Types.Piece_Types is
type Pawn is new Piece with
record
First_Move : Boolean := True;
end record;
overriding
procedure Move_Piece(Board: in CB_Vector'Class; Po: in Pawn; Move_To: in Board_Index);
-- Other piece types declared here
end Chess_Types.Piece_Types;
Chess_Types.Piece_Types.adb:
with Ada.Text_IO;
use Ada.Text_IO;
package body Chess_Types.Piece_Types is
procedure Move_Piece(Board: in CB_Vector'Class; Po: in Pawn; Move_To: in Board_Index) is
Index_From, Index_To : Board_Index;
Move_From : Board_Index := Po.Coordinate;
begin
-- Obtain locations of Pawn to move from (Index_From) and to (Index_To)
-- in terms of the single dimension vector
for I in Board.First_Index .. Board.Last_Index loop
if Board.Element(I).Coordinate = Move_From then
Index_From := I;
end if;
if Board.Element(I).Coordinate = Move_To then
Index_To := I;
end if;
end loop;
-- Determine if the requested move is legal, and if so, do the move.
-- More possibilties to be entered, very primitive for simple checking.
if Move_To - Move_From = 2 and then Po.First_Move = True then
Board.Swap(I => Index_From, J => Index_To); -- "actual for "Container" must be a variable"
Board.Element(Index_From).First_Move := False; -- "no selector for "First_Move" for type "Piece'Class"
elsif Move_To - Po.Coordinate = 1 then
Board.Swap(Index_From, Index_To); -- "actual for "Container" must be a variable"
end if;
-- Test to make sure we are in the right Move_Piece procedure
Put_Line("1");
end Move_Piece;
-- Other piece type move_piece procedures defined here
end Chess_types.Piece_Types;
As a note to understand further, the Coordinate component of each piece correspond to ICCF numeric notation, which is two digits, so there needs to be some type of conversion between the vector and the ICCF notation, hence the reason for the whole for loop at the start.
This is a tough one. It looks like limited with and generics don't play nice together. The only way to make it work is to go back to using your own access type:
with Ada.Containers.Vectors;
use Ada.Containers;
limited with Chess_Types;
use Chess_Types;
package Chessboard_Package is
subtype Board_Index is Integer range 1 .. 64;
type Piece_Acc is access all Piece'Class;
package Chessboard is new Vectors(Board_Index, Piece_Acc);
end Chessboard_Package;
I had to put the instantiation into a new package, and move the Board_Index there too. Also, I changed it to Vectors since Piece_Acc is a definite type and there's no point in using Indefinite_Vectors. But in any event, this defeats the purpose. I'm just not sure Ada gives you a way to do what you want with two packages like this.
Even doing it in one package is not easy:
with Ada.Containers.Indefinite_Vectors;
use Ada.Containers;
package Chess_Types is
subtype Board_Index is Integer range 1 .. 64;
type Color is (Black, White);
type Piece is tagged record ... end record;
type CB_Vector is tagged;
procedure Move_Piece (Board : in CB_Vector'Class;
P : in Piece;
Move_To : in Board_Index);
package Chessboard is new Indefinite_Vectors(Board_Index, Piece'Class);
type CB_Vector is new Chessboard.Vector with null record;
end Chess_Types;
This compiles, but I had to add extra stuff to get around some of the language rules (in particular, when you instantiate a generic, that "freezes" all prior tagged types so that you can no longer declare a new primitive operation of the type); also, I had to make the Board parameter a classwide type to avoid running into the rule about primitive operations of multiple tagged types.
As I understand it, this will do what you want.
with Ada.Containers.Indefinite_Vectors;
use Ada.Containers;
package Chess_Types is
subtype Board_Index is Integer range 1 .. 64;
type Color is (Black, White);
type Piece is abstract tagged
record
Name : String (1 .. 3) := " ";
Alive : Boolean := False;
Team : Color;
Coordinate : Board_Index;
end record;
type Piece_Ptr is access all Piece'Class;
package Chessboard is new Indefinite_Vectors(Board_Index, Piece_Ptr);
procedure Move_Piece (Board : in Chessboard.Vector;
P : in Piece'Class;
Move_To : in Board_Index) is abstract;
end Chess_Types;
NOTES:
Piece is now abstract, as is the Move_Piece method. This will mean you now need to derive your other piece types (package piece_type-rook.ads, with a move_piece method for rook) etc...
Chessboard now contains pointers (Class wide pointers), beware allocating, deallocating, deep copy, shallow copy issues when using it.
You should now be able to call Move_Piece on any dereference of a piece_ptr and have it dispatch to the correct method.
The Move_To parameter is now the same type as the Board_Index. (Coordinate also brought in line) -- this seems a bit clunky, perhaps rethink this. (Row & Column Indices defining a 2D array perhaps? --No need for Indefinite_Vectors)
To answer the second question in the comment:
To use First_Move, the procedure has to know that it's a Pawn. If the object is declared with type Piece'Class, you can't access components that are defined only for one of the derived types. (That's true in most OO languages.) This may indicate a flaw in your design; if you have a procedure that takes a Piece'Class as a parameter, but you want to do something that makes sense only for a Pawn, then maybe you should add another operation to your Piece that does a default action for most pieces (perhaps it does nothing) and then override it for Pawn. Other possibilities are to use a type conversion:
procedure Something (P : Piece'Class) is ...
if Pawn(P).First_Move then ...
which will raise an exception if P isn't a Pawn. If you want to test first, you can say "if P in Pawn". I sometimes write code like:
if P in Pawn then
declare
P_Pawn : Pawn renames Pawn(P);
begin
if P_Pawn.First_Move then ...
end;
end if;
But defining a new polymorphic operation is preferable. (Note: I haven't tested the above code, hope I didn't make a syntax error somewhere.)
I have a function that returns a string for a particular item, and I need to call that function numerous times and combine those strings into one. The combined string is bounded. I've made sure to fill it when space characters when it initializes but I keep getting "length check failed" errors. Is there something basic I'm doing wrong here?
FOR I IN 1..Collection.Size LOOP
Combined_String := combined_string & Tostring(Collection.Book(I));
END LOOP;
Unbounded_String is probably the easiest way to go:
with Ada.Strings.Unbounded;
use Ada.Strings.unbounded;
...
Temp_Unbounded_String : Unbounded_String; -- Is empty by default.
...
for I in 1 .. Collection.Size loop
Append(Temp_Unbounded_String, ToString(Collection.Book(I));
end loop;
If you then need to have the result placed in your fixed length standard string:
declare
Temp_String : constant String := To_String(Temp_Unbounded_String);
begin
-- Beware! If the length of the Temp_String is greater than that of the
-- fixed-length string, a Constraint_Error will be raised. Some verification
-- of source and target string lengths must be performed!
Combined_String(Temp_String'Range) := Temp_String;
end;
Alternatively, you can use the Ada.Strings.Fixed Move() procedure to bring the Unbounded_String into the target fixed-length string:
Ada.Strings.Fixed.Move(To_String(Temp_Unbounded_String), Combined_String);
In this case, if the source string is "too long", by default a Length_Error exception is raised. There are other parameters to Move() that can modify the behavior in that situation, see the provided link on Move for more detail.
In order to assign Combined_String, you must assign the full correct length at once. You can't "build up" a string and assign it that way in Ada.
Without seeing the rest of your code, I think Ada.Strings.Unbounded is probably what you should be using.
I know this is an ancient question, but now that Ada 2012 is out I thought I'd share an idiom I've been finding myself using...
declare
function Concatenate(i: Collection'index)
is
(tostring(Collection(i) &
if (i = Collection'last) then
("")
else
(Concatenate(i+1))
);
s: string := Concatenate(Collection'first);
begin
Put_Line(s);
end;
Typed off the top of my head, so it'll be full of typos; and if you want it to work on empty collections you'll need to tweak the logic (should be obvious).
Ada 2012's expression functions are awesome!
Ada works best when you can use perfectly-sized arrays and strings. This works wonderfully for 99% of string uses, but causes problems any time you need to progressively build a string from something else.
Given that, I'd really like to know why you need that combined string.
If you really need it like that, there are two good ways I know of to do it. The first is to use "unbounded" (dynamically-sized) strings from Ada.Strings.Unbounded, as Dave and Marc C suggested.
The other is to use a bit of functional programming (in this case, recursion) to create your fixed string. Eg:
function Combined_String (String_Collection : in String_Collection_Type) return String is
begin
if String_Collection'length = 1 then
return String_Collection(String_Collection'first);
end if;
return String_Collection(String_Collection'first) &
Combined_String (String_Collection'first + 1 .. String_Collection'last);
end Combined_String;
I don't know what type you used for Collection, so I'm making some guesses. In particular, I'm assuming its an unconstrained array of fixed strings. If it's not, you will need to replace some of the above code with whatever your container uses to return its bounds, access elements, and perform slicing.
From AdaPower.com:
function Next_Line(File : in Ada.Text_IO.File_Type :=
Ada.Text_Io.Standard_Input) return String is
Answer : String(1..256);
Last : Natural;
begin
Ada.Text_IO.Get_Line(File => File,
Item => Answer,
Last => Last);
if Last = Answer'Last then
return Answer & Next_Line(File);
else
return Answer(1..Last);
end if;
end Next_Line;
As you can see, this method builds a string (using Get_Line) of unlimited* length from the file it's reading from. So what you'll need to do, in order to keep what you have is something on the order of:
function Combined_String (String_Collection : in String_Collection_Type)
Return String is
begin
if String_Collection'length = 1 then
Return String_Collection(String_Collection'First).All;
end if;
Recursion:
Declare
Data : String:= String_Collection(String_Collection'First).All;
SubType Constraint is Positive Range
Positive'Succ(String_Collection'First)..String_Collection'Last;
Begin
Return Data & Combined_String( String_Collection(Constraint'Range) );
End Recursion;
end Combined_String;
Assuming that String_Collection is defined as:
Type String_Collection is Array (Positive Range <>) of Access String;
*Actually limited by Integer'Range, IIRC