/eight.adb

 1--
 2--  Project Euler problem #8
 3--
 4--  Find the greatest product of five consecutive digits in the 1000-digit
 5--  number.
 6
 7with Ada.Text_IO;
 8
 9use Ada.Text_IO;
10
11procedure Eight is
12    Source : constant String := "73167176531330624919225119674426574742355349194934" &
13                                "96983520312774506326239578318016984801869478851843" &
14                                "85861560789112949495459501737958331952853208805511" &
15                                "12540698747158523863050715693290963295227443043557" &
16                                "66896648950445244523161731856403098711121722383113" &
17                                "62229893423380308135336276614282806444486645238749" &
18                                "30358907296290491560440772390713810515859307960866" &
19                                "70172427121883998797908792274921901699720888093776" &
20                                "65727333001053367881220235421809751254540594752243" &
21                                "52584907711670556013604839586446706324415722155397" &
22                                "53697817977846174064955149290862569321978468622482" &
23                                "83972241375657056057490261407972968652414535100474" &
24                                "82166370484403199890008895243450658541227588666881" &
25                                "16427171479924442928230863465674813919123162824586" &
26                                "17866458359124566529476545682848912883142607690042" &
27                                "24219022671055626321111109370544217506941658960408" &
28                                "07198403850962455444362981230987879927244284909188" &
29                                "84580156166097919133875499200524063689912560717606" &
30                                "05886116467109405077541002256983155200055935729725" &
31                                "71636269561882670428252483600823257530420752963450";
32
33    function Digits_Product (Input : in String) return Natural is
34        Result : Natural := 1;
35    begin
36        for Item in Input'Range loop
37            Result := (Result * Natural'Value (Input (Item .. Item)));
38        end loop;
39
40        return Result;
41    end Digits_Product;
42
43    Highest : Natural := 0;
44begin
45    for Index in 1 .. (Source'Length - 5) loop
46        declare
47            Sub : constant String := Source (Index .. Index + 4);
48            Product : constant Natural := Digits_Product (Sub);
49        begin
50            if Product > Highest then
51                Highest := Product;
52            end if;
53        end;
54    end loop;
55
56    Put_Line ("> Highest product:" & Natural'Image (Highest));
57end Eight;