-- Inputs a numbers in range 0 .. 999 and prints its reverse

-- Demonstrates 2 parameter modes: In and Out
-- In mode parameters are used to send information into a procedure
-- Out mode parameters are used to send information back from a procedure
-- Default mode is In

pragma Ada_2012;  -- Make sure 2012 compiler is used.  Needed for expression functions.
with ada.text_io; use ada.text_io; 
with ada.integer_text_io; use ada.integer_text_io; 
procedure modes1  is 
    subtype Digit is Natural range 0 .. 9;
    subtype Small_Nat is Natural range 0 .. 999;

    function ones_dig(n: Small_Nat) return Digit is (n mod 10);
    function tens_dig(n: Small_Nat) return Digit is ((n / 10) mod 10);
    function hundreds_dig(n: Small_Nat) return Digit is (n / 100);

    -- Returns the digits of n1
    -- Has both In mode and Out mode parameters
    procedure find_digits(n: In Small_Nat; d1, d10, d100: Out Digit) is
    begin
        d1 := ones_dig(n);
        d10 := tens_dig(n);
        d100 := hundreds_dig(n);
    end find_digits;

    -- Returns the reverse of n1
    function reverse_it(n1: In Small_Nat) return Small_Nat is
        d1, d10, d100: Digit;
    begin
        find_digits(n1, d1, d10, d100);
        return 100 * d1 + 10 * d10 + d100;
    end reverse_it;

    s1: Small_Nat;
begin
    get(s1);

    put(reverse_it(s1));    -- Call procedure as a statement

exception
    when constraint_error => put_line("Value out of range");
    when others => put_line("Error occurred");
end modes1;

-- Input: 123
-- Output: 321