How to resolve the algorithm Middle three digits step by step in the Prolog programming language

Published on 12 May 2024 09:40 PM
#Prolog

How to resolve the algorithm Middle three digits step by step in the Prolog programming language

Table of Contents

Problem Statement

Write a function/procedure/subroutine that is called with an integer value and returns the middle three digits of the integer if possible or a clear indication of an error if this is not possible. Note: The order of the middle digits should be preserved. Your function should be tested with the following values; the first line should return valid answers, those of the second line should return clear indications of an error: Show your output on this page.

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Step by Step solution about How to resolve the algorithm Middle three digits step by step in the Prolog programming language

Source code in the prolog programming language

middle_3_digits(Number, [D1,D2,D3]) :-
    verify_middle_3_able(Number, Digits),    
    append(FrontDigits, [D1,D2,D3| BackDigits], Digits),
    same_length(FrontDigits, BackDigits).

verify_middle_3_able(Number, Digits) :-
    must_be(number, Number),
    AbsNumber is abs(Number),
    number_chars(AbsNumber, Digits),
    length(Digits, NumDigits),
    ( 3 > NumDigits         ->  domain_error('at least 3 digits',    Number)
    ; 0 is NumDigits mod 2  ->  domain_error('odd number of digits', Number)
    ; true
    ).


test_correct :-
    TestCases = [123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345],
    foreach( ( member(TestCase, TestCases),
               middle_3_digits(TestCase, Result) ),
            format('Middle 3 digits of ~w ~30|: ~w~n', [TestCase, Result])
          ).

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