Èíôîðìàòèêà


              

Çàïóñê ýòîé ïðîãðàììû íà ÝÂÌ


íà÷                                                                              cls

ââîä (à, b, ñ)                                                               input a, b, ñ

åñëè à > b òî                                                            if à > b then

òàõ := a                                                                     max = a

èíåc b > ñ òî                                                            elseif b > ñ then

òàõ := b                                                                     màõ = b

èíåc ñ > à òî                                                            elseif ñ > a then

òàõ:= ñ                                                                       màõ = ñ

êåñëè                                                                          end if

âûâîä («òàõ=»,òàõ)                                                ? «màõ=»; màõ

êîí                                                                              end

 

Çàïóñê ýòîé ïðîãðàììû íà ÝÂÌ ìîæíî ïðîâåðèòü íà ñëåäóþùèõ äàííûõ:

Tecò1                           Òåñò2                           Òåñò3

? 1 1 2                         ? 1 2 3                         ? 3 2 1

max = 2                       max = 3                       max = 3

Âñå òðè ðåçóëüòàòà ïðàâèëüíûå. Îòëàäêó ïðîãðàììû ïîñëå çàïóñêà ýòèõ ïðèìåðîâ ìîæíî áûëî áû ñ÷èòàòü çàâåðøåííîé. Îäíàêî åñòü êîíòðïðèìåð:   

                             

Êîíòðïðèìåð1

? 2 1 3

max = 2

Íî ýòîò ðåçóëüòàò - íåïðàâèëüíûé. Ñëåäîâàòåëüíî, àëãîðèòì è ïðîãðàììà ñîäåðæàò îøèáêè. Íî ñêîëüêî ýòèõ îøèáîê - îäíà, äâå, à ìîæåò áûòü áîëüøå?

Ïðè äîêàçàòåëüíîì ïîäõîäå ðàçðàáîòêà àëãîðèòìîâ è ïðîãðàìì ïðåäïîëàãàåò ñîñòàâëåíèå ñïåöèôèêàöèé è äîêàçàòåëüñòâî èõ ïðàâèëüíîñòè ïî îòíîøåíèþ ê ýòèì ñïåöèôèêàöèÿì. Ïðîöåññ ðàçðàáîòêè ïðîãðàìì ñ÷èòàåòñÿ çàâåðøåííûì ïîñëå ïðîâåðêè èõ íà ÝÂÌ è ïðåäîñòàâëåíèè äîêàçàòåëüñòâ îòñóòñòâèÿ îøèáîê.

Äîêàçàòåëüñòâà ïðàâèëüíîñòè àëãîðèòìîâ è ïðîãðàìì, ðàâíî êàê è ëþáûå äðóãèå äîêàçàòåëüñòâà, ñòðîÿòñÿ íà îñíîâå ñóæäåíèé è ðàñ­ñóæäåíèé.

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