C++课程设计学生成绩信息管理系统包括doc报告文档exe可执行文件cpp源代码以及txt格式源Word下载.docx
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time/t，就不允许修改系统时间了（缺点：
仅仅显示小时和分钟）
#include<
usingnamespacestd;
voidmain（）
{
system（"
time/t"
pause"
}
改变DOS字体颜色
colorob"
注：
当system（“colorob”）中的ob变为相应的数字时，DOS屏幕字体变为相应的颜色
改变DOS标题
title王万腾"
打印出系统日期
date"
date/t"
for_each的简单应用
#include<
vector>
string>
algorithm>
//特别注意：
for_each（）还是在algorithm头文件中定义的来
voidprint_i（intt）
{
cout<
<
t<
ends;
}
intmain（）
inta[]={1,2,3,4,5,6,7,8,9,10,11,12,13};
vector<
int>
elements（a,a+13）;
for_each（elements.begin（）,elements.end（）,print_i）;
endl;
return0;
strings（"
WangWanteng"
string:
:
size_typelen2=s.size（）;
"
s.capacity（）:
s.capacity（）<
ends<
s.size（）:
len2<
总结：
若s为一字符串，则s.size（）==s.length（）,s.capacity（）总比s.size（）或s.length（）大4个字符
string的substr（）
strings1（"
MaYu"
s1=s.substr（4,3）;
s1<
上例：
s.substr（4,3）是指从s串第（4+1）个字符开始往后数3个字符返回
关于swap（）的传说
Wangwanteng"
王万腾"
swap（s,s1）;
inta=1;
intb=2;
swap（a,b）;
a<
s<
FunctionObjects
Definition
Afunctionobjectisanobjecttowhichthefunctioncalloperatorcanbeapplied.Typically,itisaclassthatdefinesthefunctioncalloperator（operator（）（））asamemberfunction.Whenafunctionobjectisusedasafunction,thefunctioncalloperatorisinvokedwheneverthefunctioniscalled.Considerthefollowingclassdefinition:
classbiggerThanThree
public:
booloperator（）（intval）const
{returnval>
3;
}
};
IfwecreateaninstanceofclassbiggerThanThree,everytimewereferencethisobjectusingthefunctioncallsyntax,thefunctioncalloperatormemberfunctionisinvoked.Togeneralizethisclass,weaddaconstructorandaconstantdatamember,whichissetbytheconstructor:
classbiggerThan
constinttestValue;
biggerThan（intx）:
testValue（x）{}
booloperator（）（intval）const
{returnval>
testValue;
TheresultisageneralbiggerthanXfunction,wherethevalueofXisdeterminedwhenwecreateaninstanceoftheclass.Wecandoso,forexample,asanargumenttooneofthegenericfunctionsthatrequireapredicate.Inthismannerthefollowingcodefindsthefirstvalueinalistthatislargerthan12:
std:
list<
iteratorfirstBig=
std:
find_if（aList.begin（）,aList.end（）,biggerThan（12））;
3.2.2Use
Thereareanumberofsituationswhereitisconvenienttosubstitutefunctionobjectsinplaceoffunctions:
touseanexistingfunctionobjectprovidedbytheC++StandardLibraryinsteadofanewfunction;
toimproveexecutionbyusinginlinefunctioncalls;
andtoallowafunctionobjecttoaccessorsetstateinformationthatisheldbyanobject.Let'
sdealwitheachoftheseinthenextthreesections.
3.2.2.1ToEmployExistingC++StandardLibraryFunctionObjects
Table
5illustratesthefunctionobjectsprovidedbytheC++StandardLibrary.
5:
FunctionobjectsprovidedbytheC++StandardLibrary
Functionobject
Implementedoperations
Arithmeticfunctions
plus
additionx+y
minus
subtractionx-y
multiplies
multiplicationx*y
divides
divisionx/y
modulus
remainderx%y
negate
negation-x
Comparisonfunctions
equal_to
equalitytestx==y
not_equal_to
inequalitytestx!
=y
greater
greater-thancomparisonx>
y
less
less-thancomparisonx<
greater_equal
greaterthanorequalcomparisonx>
less_equal
lessthanorequalcomparisonx<
Logicalfunctions
logical_and
logicalconjunctionx&
&
logical_or
logicaldisjunctionx||y
logical_not
logicalnegation!
x
Let'
slookatacoupleofexamplesthatshowhowthesemightbeused.Thefirstexampleusesstd:
plus<
（）tocomputetheby-elementadditionoftwolistsofintegervalues,placingtheresultbackintothefirstlist.Thiscanbeperformedbythefollowingcode:
transform（listOne.begin（）,listOne.end（）,listTwo.begin（）,
listOne.begin（）,std:
（））;
Thesecondexamplenegateseveryelementinavectorofbooleanvalues:
transform（aVec.begin（）,aVec.end（）,aVec.begin（）,
logical_not<
bool>
ThebaseclasstemplatesusedbytheC++StandardLibrarytodefinethefunctionsinTable
5arealsoavailableforcreatingnewunaryandbinaryfunctionobjects.Theclasstemplatesunary_functionandbinary_functionaredefinedintheheader<
functional>
.
Thebaseclassesaredefinedasfollows:
namespacestd{
template<
classArg,classResult>
structunary_function
typedefArgargument_type;
typedefResultresult_type;
classArg1,classArg2,classResult>
structbinary_function
typedefArg1first_argument_type;
typedefArg2second_argument_type;
AnexampleoftheuseofthesetemplatesisfoundinSection
6.3.TherewewanttotakeabinaryfunctionoftypeWidgetandanargumentoftypeint,andcomparethewidgetidentificationnumberagainsttheintegervalue.Afunctiontodothisiswritteninthefollowingmanner:
structWidgetTester:
binary_function<
Widget,int,bool>
booloperator（）（constWidget&
wid,inttestid）const
{returnwid.id==testid;
Theimportanceofinheritancefromoneofthetwobaseclasstemplatesbecomesapparentwhenelementaryfunctionobjectsarecomposedtoformcomplexexpressionsusingnegatorsandbinders,whichareexplainedinSection
3.5.
3.2.2.2ToImproveExecution
Asecondreasontoconsiderusingfunctionobjectsinsteadoffunctionsisfastercode.Thedifferencebetweenafunctionandanobjectofaclassthatdefinesthememberoperator（）（）isthatfunctionsareconvertedtopointerswhenpassedasargumentstootherfunctions,thusincurringtheoverheadofafunctioncalleveniftheyaredeclaredinline.Inmanycasesaninvocationofafunctionobject,asintheexamplesonstd:
transform（）inSection
3.2.2.1,canbeexpandedin-line,eliminatingtheoverheadofafunctioncall.
3.2.2.3ToAccessorSetStateInformation
Thethirdmajorreasontouseafunctionobjectinplaceofafunctioniswheneachinvocationofthefunctionmustremembersomestatesetbyearlierinvocations.Anexampleofthisoccursinthecreationofagenerator,tobeusedwiththegenericalgorithmstd:
generate（）.Ageneratorissimplyafunctionobjectthattakesnoargumentsandreturnsanew（andpossiblydifferent）valueeachtimeitisinvoked.Themostcommonlyusedformofgeneratorisarandomnumbergenerator,butthereareotherusesfortheconcept.Asequencegeneratorsimplyreturnsthevaluesofanincreasingsequenceofnaturalnumbers（1,2,3,4andsoon）.WecancallthisobjectiotaGenafterthesimilaroperationintheprogramminglanguageAPL,anddefineitasfollows:
classiotaGen
public:
iotaGen（intstart=0）:
current（start）{}
intoperator（）（）{returncurrent++;
private:
intcurrent;
Aniotaobjectmaintainsacurrentvalue,whichcanbesetbytheconstructor,ordefaultstozero.Eachtimethefunction-calloperatorisinvoked,thecurrentvalueisreturned,andalsoincremented.Usingthisobject,thefollowingcallontheC++StandardLibraryfunctionstd:
generate（）initializesavectorof20elementswiththevalues1through20:
vector<
aVec（20）;
generate（aVec.begin（）,aVec.end（）,iotaGen
（1））;
Amorecomplexexampleofusingafunctionobjectoccursintheradixsortingexampleprogram,whichisgivenasanexampleofusingthelistdatatypeinSection
6.3.Inthisprogramreferencesareinitializedinthefunctionobject,sothatduringthesequenceofinvocationsthefunctionobjectcanaccessandmodifylocalvaluesinthecallingprogram.
IntroductiontoIterators
TheconceptofiteratorsisfundamentaltousingthecontainerclassesandtheassociatedalgorithmsprovidedbytheC++StandardLibrary.Aniteratorisapointer-likeobjectusedtocyclethroughalltheelementsstoredinacontainer.Becausedifferentalgorithmsneedtotraversecontainersinavarietyoffashions,therearedifferentformsofiterators.EachcontainerclassintheC++StandardLibrarycangenerateaniteratorwithfunctionalityappropriatetothestoragetechniqueusedinimplementingthecontainer.ItisthecategoryofiteratorsrequiredasargumentsthatchieflydistinguisheswhichalgorithmsintheC++StandardLibrarycanbeusedwithwhichcontainerclasses.
Justaspointerscanbeusedinavarietyofwaysintraditionalprogramming,iteratorscanbeusedforanumberofdifferentpurposes.Aniteratorcanbeusedtodenoteaspecificvalue,justasapointercanbeusedtoreferenceaspecificmemorylocation.Apairofiteratorscanbeusedt
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