Fibonacci series in Ada using recursion - ada

Question

In this code, I am trying to write a program that prints out the Fibonacci series based on the users' input (Index, Size). An then, the program should print out all the Fibonacci numbers between Index..Size. I have trouble, writing a recursion that calculates and prints out the Fibonacci numbers. Any suggestions?
with Ada.Text_IO; use Ada.Text_IO;
with Ada.Integer_Text_IO; use Ada.Integer_Text_IO;
with Ada.Text_IO, Ada.Unchecked_Deallocation;
procedure Fibonacci is
type Arr is array (Positive range <>) of Integer;
type Array_Access is access Arr;
Size, Index : Positive;
Variable : Array_Access;
procedure Free is new Ada.Unchecked_Deallocation (Arr, Array_Access);
procedure Recursion (Item : Arr) is --Recursion
begin
Put_Line
(Item (Item'First)'Image); --Prints out the numbers
Recursion
(Item
(Item'First + Item'First + 1 ..
Item'Last)); --Calculating the Fibonacci numbers
end Recursion;
begin
Put ("Welcome to the Fibonacci number series!");
Put
("Enter an initial value and how many Fibonacci numbers you want to print: ");
Get (Index);
Get (Size);
Variable := new Arr (Index .. Size);
Recursion (Variable);
end Fibonacci;
Example: Enter Index (the initial value of the Fibonacci series): 1
Enter Size (how many Fibonacci numbers to print): 5
The first 5 Fibonacci numbers are: 1 1 2 3 5

Answer 1

From Wikipedia,
In mathematics, the Fibonacci numbers, commonly denoted Fn, form a sequence, called the Fibonacci sequence, such that each number is the sum of the two preceding ones, starting from 0 and 1. That is,
F0 = 0
F1 = 1
and
Fn = Fn - 1 + Fn - 2
which translates pretty directly into
function Fibonacci (N : Natural) return Natural is
(case N is
when 0 => 0,
when 1 => 1,
when others => Fibonacci (N - 1) + Fibonacci (N - 2));
or, old style,
function Fibonacci (N : Natural) return Natural is
begin
if N = 0 then
return 0;
elsif N = 1 then
return 1;
else
return Fibonacci (N - 1) + Fibonacci (N - 2);
end if;
end Fibonacci;
You do have to do your printing outside the function, and admittedly there’s an inefficiency in repeatedly calculating the lower results, but you weren’t asking for efficiency.

Answer 2

Here is how you can do it (this code is based on https://rosettacode.org/wiki/Fibonacci_sequence#Recursive)
with Ada.Text_IO;
with Ada.Integer_Text_IO;
procedure Fibonacci is
First, Amount: Positive;
function Fib(P: Positive) return Positive is --Recursion
begin
if P <= 2 then
return 1;
else
return Fib(P-1) + Fib(P-2);
end if;
end Fib;
begin
Ada.Text_IO.Put_Line("Welcome to the Fibonacci number series!");
Ada.Text_IO.Put_Line("Enter an initial value and how many Kombinacci numbers you want to print: ");
Ada.Integer_Text_IO.Get(First);
Ada.Integer_Text_IO.Get(Amount);
for I in First .. First + Amount loop
Ada.Text_IO.Put("Fibonacci(" & Positive'Image(I) & " ) = ");
Ada.Text_IO.Put_Line(Positive'Image(Fib(I)));
end loop;
end Fibonacci;