《计算机科学导论》 (第三版) 第08章.ppt

《《计算机科学导论》 (第三版) 第08章.ppt》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。

1、1Objectives:Todefineanalgorithmandrelateittoproblemsolving.❑Todefinethreeconstructs—sequence,selection,andrepetition—anddescribetheiruseinalgorithms.❑TodescribeUMLdiagramsandhowtheycanbeusedwhenrepresentingalgorithms.❑Todescribepseudocodeandhowitcanbeusedwhenrepresentingalgorith

2、ms.❑Tolistbasicalgorithmsandtheirapplications.❑2Objectives(continued):Todescribetheconceptofsortingandunderstandthethreeprimitivesortingalgorithms.❑Todescribetheconceptofsearchingandunderstandtwocommonsearchingalgorithms.❑Todefinesubalgorithmsandtheirrelationstoalgorithms.❑Todis

3、tinguishbetweeniterativeandrecursivealgorithms.❑38.1ConceptInthissectionweinformallydefineanalgorithmandelaborateontheconceptusinganexample.4Figure8.1:Informaldefinitionofanalgorithm5Figure8.2:Findingthelargestintegeramongfiveintegers6Figure8.3:DefiningactionsinFindLargestalgori

4、thm7Figure8.4:FindLargestrefined8Figure8.5:GeneralizationofFindLargest98.2ThreeconstructsComputerscientistshavedefinedthreeconstructsforastructuredprogramoralgorithm.Theideaisthataprogrammustbemadeofacombinationofonlythesethreeconstructs:sequence,decision(selection),andrepetitio

5、n.Ithasbeenproventhereisnoneedforanyotherconstructs.Usingonlytheseconstructsmakesaprogramoranalgorithmeasytounderstand,debug,orchange.10Figure8.6:Threeconstructs118.3AlgorithmRepresentationSofar,wehaveusedfigurestoconveytheconceptofanalgorithm.Duringthelastfewdecades,toolshavebe

6、endesignedforthispurpose.Twoofthesetools,UMLandpseudocode,arepresentedhere.12Figure8.7:UMLforthreeconstructs13Figure8.8:Pseudocodeforthreeconstructs14Algorithm8.1:Calculatingthesumoftwointegers:15Algorithm8.2:Assigningpass/nopassgrade:16Algorithm8.3:Assigningalettergrade:17Algor

7、ithm8.4:Findingthelargestinteger:18Algorithm8.5:Findthesmallestintegersamong1000:198.4AMoreFormalDefinitionNowthatwehavediscussedtheconceptofanalgorithmandshownitsrepresentation,hereisamoreformaldefinition.Letuselaborateonthisdefinition.208.5BasicAlgorithmsSeveralalgorithmsareus

8、edincomputersciencesoprevalentlythattheyarecons