PROGRAM 5


--  Filename:  program5.adb      Author:  Anthony F. Ortiz
--  This program reads any number greater than 10 and less than 10000
--  (except for same number digits, 1, 11, 111, 1111, etc.), puts its
--  digits in a array, sorts them, subtracts descending order from
--  ascending order, prints each subtraction, and loops until the
--  number equals 6174.

with Text_IO;  use Text_IO;

--  This is the main program.
procedure Game_6174 is
    package Int_IO is new Integer_IO (Integer);  use Int_IO;
    type Int_Array is Array (0..3) of Integer;  -- An array from 0 to 3.
    Number :  Integer;                          -- Starting number.
    Number_Array :  Int_Array;                  -- Array for the digits.

--  Gets a number from the keyboard.
procedure Get_Number (Number :  in out Integer) is
begin
    Put ("Enter a 4 digit number. ");
    Get (Number);
    New_Line;
    New_Line;
    Put ("The iterations are");
    New_Line;
end Get_Number;

--  Puts each digit of the number into an array.
procedure Get_Digits (Number :  in out Integer; 
                      Number_Array :  in out Int_Array) is
    I :  Integer;  --  Count the number of digits.
begin
    I := 0;
    while (I /= 4) loop
        Number_Array (I) := Number mod 10;
        Number := Number / 10;
        I := I + 1;
    end loop;
end Get_Digits;

--  A swap procedure used for the selection sort.
procedure Swap (A :  in out Integer; B :  in out Integer) is
    Temp :  Integer;  --  Holds the value in variable A.
begin
    Temp := A;
    A := B;
    B := Temp;
end Swap;

--  Sorts the array of digits using a selection sort.
procedure Sort (Number_Array :  in out Int_Array) is
    Top          :  Integer;  --  Variable for selection sort.
    N            :  Integer;  --  Number of digits in array.
    Largestindex :  Integer;  --  Variable for selection sort.
    J            :  Integer;  --  Variable for selection sort.
begin
    N := Number_Array'Last;
    for Top in 0..N - 1 loop
        Largestindex := Top;
        for J in Top + 1..N loop
            if (Number_Array (J) > Number_Array (Largestindex)) then
                Largestindex := J;
            end if;
        end loop;
        Swap (Number_Array (largestindex), Number_array (top));
    end loop;
end Sort;

--  Subtract the descending number from the ascending number.
procedure Subtract (Number :  in out Integer; Number_Array : in Int_Array) is
    Ascending_Number  :  Integer;  --  Number with digits in ascending order.
    Descending_Number :  Integer;  --  Number with digits in descending order.
begin
    Ascending_Number := 1000 * Number_Array (3) + 100 * Number_Array (2) +
                        10 * Number_Array (1) + Number_Array (0);
    Descending_Number := 1000 * Number_Array (0) + 100 * Number_Array (1) +
                         10 * Number_Array (2) + Number_Array (3);
    Number := Descending_Number - Ascending_Number;
end Subtract;

--  Print the result of the subtraction.
procedure Print_Number (Number :  in Integer) is
begin
    New_Line;
    Put (Number, 10);
end Print_Number;

begin
    Get_Number (Number);
    while (Number /= 6174) loop
        Get_Digits (Number, Number_Array);
        Sort (Number_Array);
        Subtract (Number, Number_Array);
        Print_Number (Number);
    end loop;
end Game_6174;

--  outfile:  prog5.out

Enter a 4 digit number. 1000


The iterations are

       999
      8991
      8082
      8532
      6174




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