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1(C++)面向对象程序设计Object-OrientedProgramminginC++Chapter3KeyboardInputandScreenOutput2引入：类和对象C++程序中怎样描述“李美”同学？3引入：类和对象抽象共同特征：求平均成绩显示三科成绩及平均值学号姓

名高数成绩英语成绩C++成绩属性行为44属性行为数据函数object(方法)&&||5引入：类和对象抽象共同特征：求平均成绩显示三科成绩及平均值学号姓名高数成绩英语成绩C++成绩属性行为classstudent{intid;charname[20]

;floatscore[3];floatave;floatscore_ave();voidshow();};6classstudent{private:intid;charname[20];floatscore[3

];floatave;public:student(intn,char*na,floats1,floats2,floats3);floatscore_ave();voidshow();};student::student(intn,char*na,floats1

,floats2,floats3){id=n;strcpy(name,na);score[0]=s1,score[1]=s2,score[2]=s3;}floatstudent::score_ave()//求平均值{ave=(score[0]+score[1]+sco

re[2])/3;returnave;}voidstudent::show(){cout<<"No:"<<id<<"\t"<<"Name:"<<name<<endl;cout<<"高数:"<<score[0]<

<"\t"<<"英语:"<<score[1]<<"\t"<<"C++:"<<score[2]<<endl;cout<<"平均成绩为"<<"ave="<<ave<<endl;}7voidmain(){studentst(001,“李美",100,100,

100);st.score_ave();st.show();}8引入：类和对象classstudent{intid;charname[20];floatscore[3];floatave;floatscore_ave();voidshow();};学号姓名高数

英语C++平均学号姓名高数英语C++平均001李美100100100100填充9引入：类和对象classstudent{intid;charname[20];floatscore[3];floatave;floatscore_ave

();voidshow();};studentlm(001，“李美”，100,100,100,100）实例化主程序main(){studentlm(001,“李美",100,100,100);lm.score_ave

();lm.show();}1010补充计算机体系结构1111123.1SimpleKeyboardInputDataStreamDatastreamobjectsareusedtoperformbasicinputandoutputofdatatoandfromv

ariousdevicessuchasthekeyboardandthescreen.Astreamisadatacommunicationobjectconnectedtoaninputoroutputdevice.cout:standardoutputstreamassoc

iatedwithSCREEN<<:Theinsertionoperatorisusedtowritedatatocout.cin:standardoutputstreamassociatedwithKEYBOARD

>>:Theextractionoperatorisusedtoreaddatafromkeyboad.133.1SimpleKeyboardInputExample:eadsanumberfromthekeyboardandstoresiti

nthevariablenum14流（stream)流(stream)表示信息从源到目的端的流动，负责建立数据生产者和消费者之间的联系，数据按顺序从一个对象传送到另一对象。……C++的输入输出流是指由若干字节组成的字节序列，这些字节中的数据按顺序从一个对象传送到另一对象。流15输出流O

utputstream：数据从内存传送到某个载体或设备中；输入流Inputstream：数据从某个载体或设备传送到内存中;------------------------内存----------------------

--coutcin概念理解：输入输出(IO)流16------------------------内存------------------------coutcin概念理解：输入输出(IO)流在C++中，输入输出流被定义为类。C++I/O库中的类称为流类（streamcl

ass)。cin和cout是iostream流类的全局对象，在<iostream>中进行了定义。所以，它们在main()开始之前已经初始化。177.2.2标准输入流cinistream类的对象，它从标准输入

设备(键盘)获取数据.程序中的变量通过流提取符“>>”从流中提取数据,“>>”实际上是istream类的一个成员函数，所以cin>>coutostream类的对象，它向标准输出设备(屏幕)输出数据数据通过流插入符“>>”插入到输出流中,“<<

”实际上是ostream类的一个成员函数，所以cout<<183.2Manipulators(流操纵符)Manipulatorsareusedtomodifyinputandoutputdatastreams.endl,setw,setfill,fi

xed，setprecisionendl：skiptothestartofanewlineonthescreensetw：setthewidthofadatafieldwhichisthenumberofcolumnstha

tthedataitemoccupiesonthescreen；setfill：changethe“padding”characterfromaspacetoanyothercharacter.setw：设置数据域的宽度，即数据项在屏幕上所占的列数。只对下一个数据项起作用。所属头文件

：iomanipcout<<endl<<endl<<"endlcanbeusedanywhere"<<endlsetfill：用于把占位符从空格改变为其他字符。对所有后继项起作用。所属头文件：iomanip193.2ManipulatorsExample:Howtousemanipulat

ors#include<iomanip>Line4isrequiredforanymanipulator,likesetw,thathasavalueinparentheses.Ifthefieldwidthissettoosmalltodisplayaval

ue,thewidthisautomaticallyexpandedsothatallthedigitsinthevaluearedisplayed203.2ManipulatorsExample:Howtousesetfilland

setw•setfillchangethe“padding”characterfromaspaceto“*”•setwappliesonlytothenextdataitemintheoutputstream•setfillremainsineffectforallsubsequentdata

itemssenttotheoutputstream.213.2Manipulators(流操纵符)setprecision：指定要显示的数据的位数。对所有后继项起作用。所属头文件：iomanipfixed放置在se

tprecision之前：指定小数点后的显示位数。对所有后继项起作用。所属头文件：iomanip223.2Manipulatorssetprecision:specifythenumberofdigitsofan

umbertodisplay233.3Single-characterinputandoutputCharacterInputandOutputWhitespaceCharacters(空白字符)：generateaninvisibleblankorwhite

spaceonthescreen,suchasTab、Enterandthespacebar.Inputnoskipws:nomatterwhatitisreadfromkeyboardAlternati

vely,thefunctionget()associatedwiththeinputstreamobjectcincanbeusedOutputcoutandits<<;theoutputstreamobjectcouthasamemberfunctionput()thatcanbe

usedtodisplayacharacter;noskips：使用它能够读入空白字符。所属头文件：iomanip或者用：cin.get()显示字符：cout.put()243.3Single-characterinputandoutputExample：Howtoa

chievesingle-charinput&outputAfunctionisablockofprogramcodethatcarriesoutaspecifictask,whichwillbediscussedinfuture.•Readasinglecharacter

fromkeyboard(Includingwhitespacecharacters)25Programmingpitfalls1.Donotmixuptheinsertionoperator<<andtheextractionope

rator>>.Theinsertionoperatorisusedtoinsertdataintotheoutputstream;theextractionoperatorisusedtoreaddata

fromtheinputstream.2.Somemanipulatorsapplyonlytothenextdatafield(e.g.setw);others(e.g.setprecision)stayin

effectforallsubsequentdatafields.3.Theline#include<iomanip>isrequiredforamanipulatorthathasavalueinparenthese

s,e.g.setw(4).Othermanipulators,likeendl,donotrequirethisline.26Quicksyntaxreference27Q&A