第二章 delphi面向对象的编程方法(三)（the second chapter is delphi object-oriented programming method (three)）

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1、第二章delphi面向对象的编程方法(三)（ThesecondchapterisDelphiobject-orientedprogrammingmethod(three)）Thestatementsectionofthe2.1.8.4procedureandfunctionThestatementofaprocedureorfunctionstartswithbeginandendswithend.Thefunctionneedsareturnvalue.Youcanassignthereturnvaluetothefunctionna

2、me,oryoucanassignthereturnvaluetotheResultvariable.Thefollowingroutineassignsthereturnvaluetothefunctionname:FunctionCalculateInterest(Principal,InterestRate:,Double):Double;BeginCalculateInterest:=Principal*InterestRate;End;ItisalsopossibletoassignthereturnvaluetotheRes

3、ultvariable,andthentheaboveprogramchangesto:Result:=Principal*InterestRate;Hereisacalltothisfunction:InterestEarned:=CalculateInterest(2000,0.012);TheprocessesandfunctionsbehindtheImplementationcanandcanonlybeusedbytheeventhandlingofthislibraryelement.Tomaketheprocessand

4、functioncanbeusedinotherlibraryunit,youwillneedtheinterfacepartofthetitlesectionoftheprocedureorfunctiononthebaseunit,andthewholeprocessorfunctionwithtitleintheinplementationpartofthelibraryunit,andtheusesclauseinthelibraryunittoaccesstheprocessorfunctionofaddedtothedesc

5、riptionoftheprocessorfunctionofthebaseunit.Recursivecalltothe2.1.8.5functionInObjectPascal,theprocedureorfunctionmustfirstexplainandthencall.TheNoValuefunctionabovemustbeexplainedandexecutedbeforetheeventhandlerusingit,otherwisetheprogramwillreportanerrorwithanunknownide

6、ntifier.Theaboverulesareexceptionswhenrecursivecallsaremade.RecursivecallmeansthatthefunctionAcallsthefunctionB,andthefunctionBcallsthefunctionA.Inrecursivecalls,thefunctiontakesprecedence,i.e.,thelastwordinthetitleofthefunctionorprocessisaddedtothereservedword"forword".

7、Thefollowingroutineisatypicalexampleofarecursivecall:...ImplementationVarAlpha:Integer;ProcedureTest2(VaRA:Integer):forword;{Test2isdescribedasapreprocess}ProcedureTest1(VaRA:Integer);BeginA:=A-1;IfA>0thenTest2(A);{callTest2}thathasnotbeenexecutedbypredeclarationWriteln(

8、A);End;ProcedureTest2(VaRA:Integer);{}theexecutionpartoftheprespecifiedTest2}BeginA:=Adiv2;IfA>0rhenTes