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1、8．4NestedCallandRecursion8.4.1NestedCallStartingfromthemainfunction,themainfunctioncallsfunctionf1(),functionf1()thencallsthefunctionf2(),functionf2()thencallsthefunctionf3(),andsoon.Thisdeparturefromthemainfunctiontoformalongcallchain,isknownasNestedCall.Fig.1showsthewhole
2、process.f2()Main()f1()④③②①Callf2;Follow-upstatement;Callf1();Follow-upstatement;⑤⑧⑦⑨⑥ReturnReturnEndFig.1.NestedCallNote:Cdoesnothavenesteddefinitionsthatareavailable(可用的)insomeotherprogramminglanguages.Example1：calculateareaofcirqueAnalyse:1.areaofcirque=areaofoutercirque-
3、areaofinnercirque.2.Definetwofunction:(1)circleArea:calculateareaofcircle;(2)ringArea:calculateareaofcirque.Program:#include#definePI3.14doublecircleArea(doubler)/*calculateareaofcircle*/{returnPI*r*r;}doubleringArea(doubler1,doubler2)/*calculateareaofcirque*/{if(r
4、1<=r2)returncircleArea(r2)-circleArea(r1);elsereturncircleArea(r1)-circleArea(r2);}voidmain(){doubler1,r2,s;printf(“tInputr1,r2:”);scanf(“%lf%lf”,&r1,&r2);s=ringArea(r1,r2);/*callfunction*/printf("tTheareais:%.2lf“,s);}8.4.2RecursionCfunctionsmaybeusedrecursively;that
5、is,afunctionmaycallitselfeitherdirectlyorindirectly.Functionsarecalleddirectlyorindirectlythemselvsisknownasrecursion.Fig.2showstheprocessofRecursion.f1()Callf1()f1()Callf2()f1()Callf2()(a)Directlycallsitself(b)IndirectlycallsitselfFig.2TheprocessofrecursionExample2：factori
6、als(n!)Analyse：n!=n*(n-1)*(n-2)…2*1;n!=n*(n-1)!;(n-1)!=(n-1)*(n-2)!;(n-2)!=(n-2)*(n-3)!;…2!=2*1!;1!=1Program:#includelongfac(intn){longf;if(n==0
7、
8、n==1)f=1;elsef=n*fac(n-1);printf("t%d!=%ld",n,f);returnf;}voidmain(){printf("t5!=%ld",fac(5));}Exercise8-4-1.Wr
9、iteaprogramtoprintanumberasacharacterstringfromhigh-orderdigitstolow-orderdigits.Analyse：Wecanuserecursivesolutiontodealwiththisprobleminwhichprintdfirstcallsitselftocopewithanyleadingdigits,thenprintsthetrailingdigit.Again,thisversioncanfailonthelargestnegativenumber.Refer
10、enceprogram:#include/*printd:printnindecimal*/voidprintd(intn){if(n<0){pu
