C++ programing for beginners€¦ · • Functions can be - like miniature programs; - put together to form a large program. • Function can be categorized: - predefined functions;

Lecture4

C++programingforbeginners

1May2019

Lecturer:Dr.AnleWang&Dr.SergeySukhomlinov

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E-mail:[email protected]

mailto:[email protected]

Lecture4

• Learnaboutstandardfunctionsanddiscoverhowtousetheminaprogram;abs(x)• Learnaboutuser-definedfunctions;• Examinevalue-returningfunctions;• Explorehowtoconstructanduseauser-definedfunctioninaprogram;

• Afterthislecture,youshouldbeableto:✓Constructanduseauser-definedfunction;

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ContentsofLecture4

• Functionsarelikebuildingblocks;• Advantagesofusingfunctions:- Allowcomplicatedprogramstodividedintomanageablepieces;- Focusonthispartofprogramandconstructit,debugitandmakeitperfect;- Differentprogrammercanworkondifferentfunctionsinparallel;- Canbere-used;- Enhanceprogramreadability.

Whatisafunction?

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• Functionscanbe- likeminiatureprograms;- puttogethertoformalargeprogram.

• Functioncanbecategorized:- predefinedfunctions;sqrt(x),abs(x)…- user-definedfunctions.

Whatisafunction?


• Mathfunctionsincmathheader;suchassqrt()• Predefinedfunctionsarecategorizedbyseparatelibraries;• sqrt(),abs(),floor(),ceil(),min(),max()…

Predefinedfunctions


• User-definedfunctionsarenamedsectionsofcodecanbecalledfromanywhereintheprogram;•

User-definedfunctions


• Theruletonamethefunctionisthesameasnamingvariables.• Trytoavoidtogivethesamenameofpredefinedfunctions.



• Parameterspassedbyvalue;• Thereturntypenameofafunctionisthetypethatthefunctionevaluatestowhencalled;• Theargumentcanbechangedwithinthefunctionwithoutchangingthevaluesoutsidethefunction;



• Functionparametersarevariableswithatypeandaname,separatedwithacomma;formalparameter• Theargumentsareinscopeofthefunctionbody;• Withoutparameters,requireparentheses:funtion();



• Functionbodycancontainanycode,justlikemainfunction;• Functionalsocancallotherfunction,includingthemselves(recursion).



• Specifiedthevalueofthefunctionevaluatesto;• Exitthefunctionandreturnthecodethatcalledit;• Canoccuranywhereinthefunctionbody(if);• voidfunctionneedsnoreturnstatement.



• Thereturnvalue0ofmainfunctionmeansthefunctionexitsnormallyandendssuccessfully.- return0:theprogramwassuccessful;- returnEXIT_SUCCESS:theprogramwassuccessful;(cstdlib.h)- returnEXIT_FAILURE:theprogramfailed.(cstdlib.h)

Returnvalueofmainfunction


• Functionsmustbedeclaredbeforetheyarecalled;- thewholefunctioncanbeputabovetheplaceitisplaced;- orthedeclarationcanbeputabovetheplaceitisplaced,andthefunctiondefinitionbelow.



• Theprogramstartsexecutionfrommainfunction;• Thenwhenthefunctioniscalled,executethefunction;• Afterthefinalstatementofthefunctionisexecuted,jumpbackimmediatelytothepointfollowingthefunctioncalled.

Executionflow


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• voidfunctiondoesnotreturnanyvalue.• Formalparameterisoptional(alsoinvalue-returnfunction);• Callvoidfunctionwith();

Voidfunction


• Globalvariables:identifiersdeclaredoutsideofeachfunctiondefinition• Localvariables:identifiersdeclaredwithinafunction.•

Localandglobalvariables


• Whenmorethanonefunctionusetheglobalvariables,sometimessomethinggoeswrong:- Hardtofindthereasonandtheplacewentwrong;- Problemcausedbythisareamaycauseerrorinthatarea;

• TRYTOUSEGLOBALVARIABLECAREFULLY!• Localvariablesonlycanbeappliedinthescopeofthisfunction.

Localandglobalvariables


• Severalfunctionscanhavethesamename;• Twofunctionshavedifferentformalparameterlists;- Differentnumberofparameters;- Samenumberofparameterswithdifferentdatatype;

• Functionoverloading:createseveralfunctionswithsamename.

• Writeasmallprogramtocomparetwoorthreenumbersandfindtheminimumonewithfunctionoverloading;

Functionoverloading


• Functioncanbecalledbythemselves,usefulforsortingelements,recursivefunctions…• Avoidinfiniteloopwithsomebasiccontrolstructures.

Recursivenessoffunction


Recursivenessoffunction


forloop

forloopwithcallingfunctionrecursivefunction

• valueparameter:aformalparameterthatreceivesacopyofthecontentofcorrespondingactualparameter;• referenceparameter:aformalparameterthatreceivethelocation(memoryaddress)ofthecorrespondingactualparameter.•

Valuevariables,referencevariables


• Intheexample,wewilltrytowriteaprogramtodeterminethemaximumandminimumnumberofanintegernumberarray.14172536549012• Thestructureofmainfunction:- initializethevariables,setthenumberofintegers,initialmaximumandminimumvalues;- Readanumberfromkeyboard;- Comparethenumberwithinitialmaximumandminimumvalue,ifconditionfulfills,replacetheinitialvaluewiththisnumber;- repeatstep2and3withreadingthenumberlist;- Displaytheresultofmaximumandminimumvalue.

Programingexample


• Foreachstep,definethefunction:- initializethevariables,setthenumberofintegers,initialmaximumandminimumvalues;initParams()- Readanumberfromkeyboard;inputNum()- Comparethenumberwithinitialmaximumandminimumvalue,ifconditionfulfills,replacetheinitialvaluewiththisnumber;maximum(),minimum()- repeatstep2and3withreadingthenumberlist;loopstructure- Displaytheresultofmaximumandminimumvalue.dispResult()

Programingexample


• Themainfunctioncanbe:

Programingexample


• 1.Initializethevariables,setthenumberofintegers,initialmaximumandminimumvalues;initParams()• Trytofigureoutwhichisglobalvariableandlocalvariable.•

Programingexample


• 2.Readanumberfromkeyboard;inputNum()

• 3.Comparethenumberwithinitialmaximumandminimumvalue,ifconditionfulfills,replacetheinitialvaluewiththisnumber;minimum(),maximum()•

Programingexample


• 4.Displaytheresultofmaximumandminimumvalue.dispResult()

Programingexample


Programingexample


• Writeaprogramcontainstwofunctionsminimum()andmaximum()tocomparetwointegernumbers;• Writeafunctiontodetermineiftheinputnumberisaprimenumber,thenumbercanbeinputinmainfunction.• Writeafunctiontogetthevalueofa!+b!+c!,inputandoutputthevaluebymainfunction.

Exercises


Lecture4

• Firstandsecond-orderalgorithm;• Precisionanderror;

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C++ programing for beginners€¦ · • Functions can be - like miniature programs; - put together to form a large program. • Function can be categorized: - predefined functions;