C___ an Introductory Guide for - Francis John Thottungal
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An introduction to c++, variables, reserved words
Transcript of C___ an Introductory Guide for - Francis John Thottungal
C++
AnIntroductoryGuide
ForBeginners
FrancisJohnThottungal
C++
AllRightsReserved
Copyright©2015FrancisJohnThottungal
Thisbookmaynotbereproduced,transmitted,orstoredinwholeorinpartbyanymeans,includinggraphic,electronic,ormechanicalwithout theexpresswrittenconsentof thepublisherexcept in thecaseofbriefquotationsembodied incriticalarticlesandreviews.
Booktango
1663LibertyDrive
Bloomington,IN47403
www.booktango.com
877-445-8822
ISBN:978-1-4689-6322-9(ebook)
ContentsOverview
1–Thefirstprogram
1.0Thefirstprogram
1.1Comments
1.2Usingnamespace:std
1.3Variables
1.4FundamentalDataTypes
1.5DeclarationofVariables
1.5.1IntroductiontoStrings
1.5.2Operators
1.5.3Precedenceofoperators
1.5.4Scopeofavariable
2–I/O
2.0InputandOutput
2.1cout
2.2cin
3–Theflowcontrol
3.0Statements
3.1Ifandelse
3.2Loops
3.3Jumpstatements
3.4Switch
4–Functions
4.0Definitionofafunction
4.1Functionsthatdonotreturnavalue
5–Arrays
5.0WhatareArrays
5.1SimpleArrays
5.2Accessinganelementofanarray
5.3Multi-dimensionalArrays
6–Pointers
6.0WhatarePointers
6.1Pointerconcepts
7–Strings
7.0CharacterString
7.1StringFunctions
8–References
8.0WhatareReferences
9–File
9.0Inputandoutputwithfiles
9.1Openingafile
9.2Closingafile
9.3TextFiles
10–StorageClasses
10.0Typesofstorageclasses
11–Classes
11.0Buildingclasses
11.1Classconcepts
12–Inheritance
12.0TheconceptofInheritance
12.1SomeOOP’sterms
13–Exceptions
13.0Errorhandling
14–Conclusion
OverviewC++isgenerallyalanguagetaughttotechnicalstudentsincollegearoundtheworld.ThemainreasonC++,aderivativeofC,hasbecomeimportantisthatitisusedinprettymuchanything of a serious kind in programming such as developing drivers, graphical userinterfaces,operatingsystemsetc.
It is a technical language apt for technologists. However, anyone who is interested inprogrammingcanmasteritwithsomeeffort.Thislanguagehastwopartstoit-standaloneandobjectoriented.
Theapproach:Inthisguide, theapproachis toemphasizethebasicbuildingblocksofaC++program.Theemphasis is tohelpone tomakesimplestandaloneprograms.Theexamples in thisguidearerelativelysmallandperhapsacademic.
Onecandownloadthezipfileofallexamplecodeusedinthisguideatthelocationgivenattheendofthebook.
SoftwareUsed:TherearemanyC++editorsinthemarket.IusedtheMicrosoftVisualExpress2010.
To use this software or its latest version, just install the express version or full versionafterdownloadfromhttp://www.microsoft.com.
Youmaywanttodoasearchforeditorsespeciallyifusenon-windowsbasedcomputerssuchasLinuxorMac.
Asthis isnotatextbook, thegoalof thisguideis justforaquickstart tounderstandinghow towrite basicC++ code. It is intended for those completely new to the subject orprogramming in general. Itmight also serve thosewhoprefer less technical jargon andsimpleexamplestogetagraspofthelanguage.
Youmayviewordownload the instructionsandscreenshotsforusingMicrosoftVisualStudioorExpressversionsatthewebsitestatedattheendofthebook.
1Thefirstprogram
“Comeforthintothelightofthings,letnaturebeyourteacher.”—WilliamWordsworth
1.0ThefirstprogramThefirstprogramusuallywritteninanyprogramminglanguageclassisonethatdisplaystheword“HelloWorld”.Thisisakindofanunwrittentradition.Letuswritethecodeforthatnow:
#include<iostream>
intmain()
{
std::cout<<“HelloWorld!”;
}
Intheabovecode:
Ahashsign(#)indicatesdirectivesreadandinterpretedbythepre-processor.
Theintmain()isthedeclarationofafunction.AllC++programshaveamainfunction.
Theopenbrace({)indicatesthebeginningofmain’sfunctiondefinition,andtheclosingbrace(}),indicatesitsend.
Thestd::cout<<“HelloWorld!”isaC++statementtobeexecuted.
Here<<meansinsertionandcoutisthekeywordthatisneededtooutputthetext
Allstatementendswithasemicolon(;).Onecanenterblanklinesbetweenlinestomakethecodereadable.
InC++,onecanwriteseveralstatementsinasingleline,oreachstatementcanbeinitsownline.
Now, let us add an additional statement to our first program.Theoutput of the code isHelloWorld!MyC++program.Inotherwords,thetwostatementsareonthesameline.
Toavoidthisuseendlattheendofeachstatement.
#include<iostream>
intmain()
{
std::cout<<“HelloWorld!”;
std::cout<<“MyC++program”;
}
#include<iostream>
intmain()
{
std::cout<<“HelloWorld!”;<<endl;
std::cout<<“MyC++program”;<<endl;
}
1.1CommentsC++supportstwowaysofcommentingcode:
//linecomment
/*blockcomment*/
One canwrite short comments using the line comment. The block comments are usedwhenlargeramountoftextisrequiredinthecomments.
Letusaddcommentstoour“HelloWorld”program:
Wewilluseblockcommentsatthebeginningoftheprogramandlinecommentsforthestatements.
/*Thisisablockcomment.Thisprogramiswrittentoshowtheusageofcomments-blockandline*/
#include<iostream>
intmain()
{
std::cout<<“HelloWorld!”;//printsHelloWorld!
}
1.2Usingnamespace:stdByusingthenamespacestdwecanavoidwritingstd::couteverytimewewantsomethingwrittentothescreen.Forexample:
/*AprogramtowriteHelloWorld.Thisdemonstratestheuseofblockcomments*/
#include<iostream>
usingnamespacestd;
intmain()
{
cout<<“HelloWorld!”;//printsHelloWorld!
}
1.3VariablesVariablescanbefoundinmathematics.Youmusthaveseenstatementssuchas:
A=1;ora=5;ora+b=cetc.
Variablesholdvaluesordataforaperiodandreferenceaparticularareaofmemory.Likemany other programming languages, C++ uses variables. Each variable should have adistinctnameoridentifier.Insteadofcallingavariablebythelettersofthealphabet,wecouldgivethevariableusefulnamessuchasresultaslongasthenameisnotreservedasanexclusiveC++identifier.
A valid identifier or variable name is a sequence of one or more letters, digits, orunderscorescharacters(_).Spaces,punctuationmarks,andsymbolscannotbepartofanidentifier.Inaddition,identifiersshallalwaysbeginwithaletter.Theycanalsobeginwithanunderlinecharacter.Innocasecanitbeginwithadigit.
C++languageiscasesensitivesoacapitalvariableidentifierisdifferentfromlowercasevariableidentifier.
SomeexamplesofreservedidentifiersinC++are:
Thelistisonlyapartialone.
asm else new
auto enum operator
bool explicit private
break export protected
case extern public
catch FALSE register
char float reinterpret_cast
class for return
const friend short
const_cast goto signed
continue if sizeof
default inline static
delete int static_cast
do long struct
double mutable switch
Specificcompilersmayhaveadditionalreservedwords.
1.4FundamentalDataTypes• Charactertypes:Theycanrepresentasinglecharacter,suchas‘A’or‘$’.Themost
basictypeischar,whichisaone-bytecharacter.(ex:Char)
• Numericalintegertypes:Theycanstoreawholenumbervalue,suchas7or1024.Theyexistinavarietyofsizes,andcanbeeithersignedorunsigned,dependingonwhethertheysupportnegativevaluesornot.(ex:int)
• Floating-point types: They can represent real values, such as 3.14 or 0.01, withdifferentlevelsofprecision,dependingonwhichofthethreefloating-pointtypesisused.(ex:float,double)
• Booleantype:TheBooleantype,knowninC++asbool,canonlyrepresentoneoftwostates,trueorfalse.(ex:bool)
1.5DeclarationofVariablesTodeclareavariableoftypeintegerwewriteasfollows:
inta;
intb;
floatfirstnumber:
doublew;
chara;
Wecanalsodeclaremorethanonevariableofthesametypeinasinglelineasfollows:
intx,y,z;
Onecaninitializevariables.
intx=0;
#include<iostream>
usingnamespacestd;
intmain()
{
intx=5;//initialvalue:5
inty=2;//initialvalue:2
intz;
z=x+y;
cout<<z;
return0;
}
Sometimesitisconvenienttogiveaconstantvaluetoavariable.Forexample:
constpi=3.1415926;
However if you declare pi without const also the program will work. Most first timeprogrammersfromobservationdonotusetheconstvariabledefinition.
1.5.1IntroductiontoStringsWhile a character represents a single symbol such as ‘A’ or a ‘$’ a string represents acompoundtypeinC++.
Touseastringweneed to includeanewdirective# include<string> inaddition to thedirectiveiostream.
Weusecouttooutputthevalueofxtothescreen.
//Anexampleofastring
#include<iostream>
#include<string>
usingnamespacestd;
intmain()
{
stringx;
x=“Thisisanexampleofastring”;
cout<<x;
return0;
}
Intheexampleabovetheoutputwouldbethestring:
Thisisanexampleofastring
1.5.2OperatorsOperatorsareusedonvariablesandconstants.Thereareseveraltypesofoperators.
ThemostcommonoftheoperatorsinC++are:
• Assignmentoperators(=):
x = 2; The assignment operation always takes place from right to left. So here, x isassignedthevalueof2.
y = z; The statement assigns the value contained in z to the variable y. The valuecurrentlyinyislostandreplacedwiththevalueinz.Ifzchangesatalatermoment,itwillnotaffectthenewvaluetakenbyy.
//assignmentoperator
#include<iostream>
usingnamespacestd;
intmain()
{
intx,y;
x=5;//x:5,y:
y=2;//x:5,y:2
x=y;//x:2,y:2
y=3;//x:2,y:3
cout<<“x:”;
cout<<x;
cout<<“y:”;
cout<<y;
}
• ArithmeticOperators(+,-,*,/,%):
The fivearithmeticaloperations supportedbyC++are common toalmost all languagesandsomethingoneisfamiliarwithfrommathematics.
Theyare:
Operator Description
+ Addition
- Substraction
* Multiplication
/ Division
% Modulo
Themodoluoperatorgivestheremainderofadivisionoftwovalues:Forexample:
x=10%4;willgivethevalueof2tox.
• CompoundAssignment(+=,-=,*=,/=,%=,>>=,<<=,&=,^=,|=)
Compoundassignmentoperatorsmodifythecurrentvalueofavariablebyperforminganoperationonit.Forexample:
a+=x;meansa=a+x;
x-=10;meansx=x-10;
y/=x;meansy=y/x;
z*=x;meansz=z*x
• IncrementandDecrement(++,—)
These operators increase or decrease by one (1) the value stored in a variable. This isequivalentto+=1and--1respectively.
Thus++y;
y+=1;
y=y+1;
areallequivalentinitsfunctionality.Theyallincreasebyonethevalueofy.
Sodoesitmakeadifferenceifthe++isbefore(prefix)orafterthevariable(suffix)?
Yesitdoes:
Example1 Example2
z=5 z=5;
y=++z; y=z++
Herezis6,yis6 Herezis6yis5
In other words in Example 1, the value assigned to y is the value of z after beingincreased.InExample2,thevalueassignedtoyisthevalueofzbeforebeingincreased.
• Relationalandcomparisonoperators(==,!=,>,<,>=,<=)
Twoexpressions canbe comparedusing relational and equalityoperators.The result ofsuchanoperationiseithertrueorfalse.TherelationaloperatorsinC++are:
Operator Description
== Equalto
!= Notequalto
< Lessthan
> Greaterthan
<= Lessthanorequalto
>= Greaterthanorequalto
Thus:
(7==8)isfalse
5>3istrue
1!=2istrue
7>=7istrue
9<=8isfalse
Theassignmentoperator(=)isnotthesameastherelationaloperator(==).Oneassignsthevalueontherighthandsidetothevariableontheleftandtheothercompareswhethervaluesonbothsidesoftheoperatorareequal.
• Logicaloperators(!,&&,||)
Theoperator!istheC++operatorfortheBooleanoperationNOT.Thus:
!(7==7)isfalse
!(7<=5)istrue
!(9>5)isfalse
!(10<=8)istrue
The logical operators && and!! are used when evaluating two expression to obtain asinglerelationalresult.The&&isequivalenttotheBooleanlogicaloperationANDwhichhasthefollowingtruthtable.
x y x&&y
True True True
True False False
False True False
False False False
The || logical operator is equivalent to theBoolean logical operationORwhich has thefollowingtruthtable.
x y x||y
True True True
True False True
False True True
False False False
• Conditionalternaryoperator(?)
The conditional operator returns one value if the expression evaluates to true and adifferentoneiftheexpressionevaluatestofalse.Itssyntaxis:
condition?result1:result2
ThisissimilartousingtheIFcondition.Wewilldiscussthisinthecontrolschapter.
Fornow:
9==7?5:3 willgivetheresult3because9and7arenotequal
7==6+1?5:3 willgivetheresult5
Letuslookatanexample:
//conditionaloperator
#include<iostream>
usingnamespacestd;
intmain()
{
intx,y,z;
x=1;
y=5;
z=(x<y)?5:x;
cout<<z<<‘\n’;
}
Inthecodeabovetheresultwouldbe5because1islessthan5.Haditbeengreaterthanythentheresultwouldgivethevalueofx.
• CommaOperator(,)
Thecommaoperatorseparatestwoormoreexpressions.Forexample:
x=(y=5,y+7);
Thiswouldassign thevalueof5 toyand thenassigny+7 tox.Theresultwouldx=9whiley=5.
• Bitwiseoperators(&,|,^,~,<<,>>)
Bitwiseoperatorsmodifyvariablesconsidering thebitpatterns that represent thevaluestheystore.
Operator Equivalent Description
& AND BitwiseAND
| OR BitwiseinclusiveOR
^ XOR BitwiseexclusiveOR
~ NOT Unarycomplement
<< SHL Shiftbitsleft
>> SHR Shiftbitsright
• Explicittypecastingoperator
Typecastingoperatorsallowconversionofavalueofagiven type toanother type.Forexample:
intx;
floaty=3.15;
x=(int)y;
Herethexwillbe3.Anotherwayofwritingthelaststatementwouldbe:
x=int(y);
BothwaysarevalidinC++.
• Sizeofoperator
Thisoperatoracceptsoneparameter,whichcanbeeitheratypeoravariableandreturnsthesizeinbytesofthattypeorobject.
y=sizeof(char);
Hereywillgetthevalue1becausecharisatypewithasizeof1byte.Thevaluereturnedbysizeofisacompiletimeconstantsoitisalwaysdeterminedbeforeprogramexecution.
1.5.3PrecedenceofoperatorsAsingleexpressionmayhavemultipleoperators.Forexample:
z=7+8/2;
Sowheredoonestart?
Hadthisbeenwrittenas:z=7+(8/2); itwouldhavebeeneasieras thebracket itemswillbeevaluatedfirstbecauseofprecedence.7+4=11.Thetablebelowsummarizestheprecedenceorder.
Level Precedencegroup Operator Description Grouping
1 Scope :: scopequalifier Left-to-right
2 Postfix(unary) ++,—,(),[] Increment,decrement,bracket. Left-to-right
3 Prefix(unary) ++,—,|! prefixincrement/decrement,not,logicalnot Right-to-left
4 Pointer-to-member .*->* accesspointer Left-to-right
5 Arithmetic:scaling */% multiply,divide,modulo Left-to-right
6 Arithmetic:addition +- addition,subtraction Left-to-right
7 Bitwiseshift <<>> shiftleft,shiftright Left-to-right
8 Relational <><=>= comparisonoperators Left-to-right
9 Equality ==!= equality/inequality Left-to-right
10 And & bitwiseAND Left-to-right
11 Exclusiveor ^ bitwiseXOR Left-to-right
12 Inclusiveor | bitwiseOR Left-to-right
13 Conjunction && logicalAND Left-to-right
14 Disjunction || logicalOR Left-to-right
15 Assignment-levelexpressions
=*=/=%=+=-=>>=<<=&=^=|=
assignment/compoundassignmentRight-to-left
?: conditionaloperator
16 Sequencing , commaseparator Left-to-right
1.5.4ScopeofavariableWehavelookedintovariabledeclaration.Variablescanbelocalorglobal.
Variablesdeclaredinsideafunctionorblockarelocalvariables.Onlystatementsthatareinside that function or block of code can use them. Local variables are not known tofunctionsoutsidetheirown.
Globalvariablesaredefinedoutsideofall the functions,usuallyon topof theprogram.Theglobalvariableswillholdtheirvaluethroughoutthelifetimeofyourprogram.
Aglobalvariablecanbeaccessedbyanyfunction.Thatis,aglobalvariableisavailableforusethroughouttheentireprogram.
Wewilllookattwoexamples:
#include<iostream>
usingnamespacestd;
intmain()
{
intx,y;
intz;
x=10;
y=20;
z=x+y;
cout<<z;
return0;
}
#include<iostream>
usingnamespacestd;
intt;
intmain()
{
x=10;
y=20;
t=x+y;
cout<<t;
return0;
}
Inthetableontheleft,thereareonlylocalvariables.Theoutputwillbe30.
Thesecondtablehasadeclarationfortoutsidemainfunction.Themainfunctionusesittoprintthevalueoft,whichremainsat30.
C++allowsforglobalvariablesandlocalvariablestobethesame-butitisbestnottousethemthatway.
2I/O
“Thegreatestsignofsuccessforateacher…istobeabletosay,‘ThestudentsarenowworkingasifIdidnotexist.’”—MariaMontessori
2.0InputandOutputWewilllookatcinandcouthere.
Stream Description
cin standardinput
cout standardoutput
cerr standarderror–output
clog standardlogging-ouput
2.1coutcoutisusedwith<<whichisusedforinsertion.
Eachcoutlineproducesalineofwordsonaseparatelineonlyiftheendline\norendlisused.
Otherwise,thelineswillbewrittenoneaftertheotheronthesameline.
cout<<“Sentence1”;//printsSentence1
cout<<100;//prints100
cout<<x;//printsthevalueofx
Text is enclosed in double quotes as shown in previous example. Multiple insertionoperations(<<)maybechainedinasinglestatement.
cout<<“Thisis”<<“a”<<“avalidstatement”;
Whatcoutwillnotdoautomaticallyisaddlinebreaksattheend,unlessinstructedtodoso.Soifonewritesthefollowinglinesofcode:
cout<<“Thisisline1.”;
cout<<“Thisisline2.”;
Then the output will be in a single line without any line breaks in between as shownbelow:
Thisisline1.Thisisline2.
Toinsertalinebreak,anewlinecharactershouldbeincludedasfollows:
cout<<“Thisisline1.\n”;
cout<<“Thisisline2.\n”;
Nowtheoutputwillbe:
Thisisline1.
Thisisline2.
Anotherwayistouseendl.Forexample:
cout<<“Thisisline1.”<<endl;
cout<<“Thisisline2.”<<endl;
2.2cinThestandardinputbydefaultisthekeyboardandwewillnowlookatcinasthestreamobjecttoaccesswhatistobeinput.
intx;
cin>>x;
Thevalueofxcanbeentered.
Wewillusebothcinandcoutinthisexample.
//exampleofcinandcout
#include<iostream>
usingnamespacestd;
intmain()
{
floatx;
cout<<“Pleaseenteranumber:”;
cin>>x;
cout<<“Thevalueyouenteredis”<<x;
cout<<“anditsdoubleis”<<x*2<<“.\n”;
return0;
}
Here the program asks for a number of type float (ex: 3.14) and gives its double.Therefore, if we entered 5.0 then the output would be 10.0. If you are running thisprogramasastandalone,youmayseethecommandwindowclosingveryfast.Inthiscaseentercin.get();aftersecondandthirdcoutstatements.
Likecout,onecanchaincintorequestmorethanonedatainasinglelinestatement.Forexample:
cin>>x>>y;
isequivalentto:
cin>>x;
cin>>y;
Letusnowlookatanexamplewherecin,coutisusedtogetastringfromthekeyboard.When writing a console-based program in C++, cin might not effectively capture thestring.Therefore,wehavetointroduceafunctioncalledgetlineintheexamplebelow:
//cin,cout,getline
#include<iostream>
#include<string>
usingnamespacestd;
intmain()
{
stringx;
cout<<“What’syourname?”;
getline(cin,x);
cout<<“Hello”<<x<<“.\n”;
return0;
}
getlinewill call cin alongwith the stringvariablex. x stores thevaluesof thequestionbeingaskedintheprogram.
Ifyouareusingthis isaconsoleprogramyoumayhavetowritecin.get();after thelastcoutstatementtokeepthecommandwindowfromclosing.
3Theflowcontrol
“Theimportantthinginlifeisnotthetriumphbutthestruggle.”—PierredeCoubertin
3.0StatementsBynow,youare familiarwith thegeneral layoutofaC++program.Statementsare theindividualinstructionsofaprogramforexample-variabledeclarationandexpressions.
In a C++ program, a statement can be a simple one line statement terminated by asemicolon(;)oracompoundstatement.
Compound statement is a group of statements each terminated by a semicolon (;) andgroupedtogetherinablockenclosedincurlybrackets{}asfollows:
{
floatx;
cout<<“Pleaseenteranumber:”;
cin>>x;
cout<<“Thevalueyouenteredis”<<x;
cout<<“anditsdoubleis”<<x*2<<“.\n”;
return0;
}
3.1IfandelseThe if keyword is found in several programming languages. It is used to execute astatementorblockifandonlyifaconditionisfulfilled.
if(condition)statement
if(x<100)
cout<<“xislessthan100”;
If thecondition isnotmet,nothing isprintedout. If therearemultiple statements tobeexecuted when the condition is fulfilled, then these statements should be enclosed inbracketsformingablock.
Forexample:
if(x<100)
{
cout<<“xislessthan100”;
cout<<x;
}
Thecodeabovecanbemadeonasinglelineasfollows:
if(x<100)
{cout<<“xislessthan100”;cout<<x;}
Generally,beginnersaremorecomfortablewithwritinga statementon itsown lineandthis can increase the readability of the code. The elsekeyword is used to introduce analternativestatement.Thesyntaxis:
If(condition)statement1elsestatement2
Forexample:
if(y==10)
cout<<“yisequalto10”;
else
cout<<“yisnot10”;
Soherethestatementyisequalto10willprintif(y==10)otherwisethestatementyisnot10willprint.
3.2LoopsLoops are known as iteration statements. That is because one uses loops to repeat astatement a certain number of times while a condition is fulfilled. The loop uses thekeywords-while,doandfor.
Awhileloophasthefollowingsyntax:
while(condition)statement
//exampleofwhileloop
#include<iostream>
usingnamespacestd;
intmain()
{
inty=3;
while(x>0){
cout<<y<<“,”;
—y;
}
cout<<“Endofloop\n”;
}
Theoutputofthiscodewouldbe3,2,1,EndofLoop.Tocontrolthecommandwindowuse cin.get(); after the last cout if necessary. If after any executionof the statement theconditionbecomefalsethentheloopendsandtheprogramcontinuesrightaftertheloop.
Inthiscase,theconditionwasxhadtobegreaterthanzero.Sowhenitcountsfromfivedownwardsoneata timedueto(—x)itwillstoptheloopafteronewhenxwillnotbegreater than zero. Then it jumps the loop and goes to the next available line in theprogram,whichinthiscaseisthecoutstatement.Thus,itwillprint“Endofloop”.
Inallloops,theremustbeanexitpoint.Otherwise,itwillgoonforever.
do-whileloop
Thesyntaxforthistypeofloopis:
dostatementwhile(condition);
The condition is evaluated after the statement has been executed. Thus, at least oneexecutionofthestatementisdoneeveniftheconditionisnotfulfilled.Forexample:
//do-whileloop
#include<iostream>
#include<string>
usingnamespacestd;
intmain()
{
stringx;
do{
cout<<“Enteryourusername:”;
getline(cin,x);
cout<<“Youentered:”<<x<<‘\n’;
}while(x!=“student”);
}
Hereletuslookattheoutputbasedontheinput:
Enteryourusername:hello
Youentered:hello
Enteryourusername:student
Youentered:student
Soatleastonetimetheloophastobeexecutedevenifoneentersstudenttoexitthelooplikeinthiscase.Thisfeatureofdoisthereasonwhyonemayselectitoverwhile.
TheforloopThesyntaxforthistypeofloopisasfollows:
for(initialization;condition;increase/decrease)statement;
Likethewhileloopthistypeoflooprepeatsstatementswhileconditionistrue.Inadditiontheforloopprovidesaninitializationandincrease/decrease(change)expressionexecutedbeforetheloopbeginsforthefirsttimeandaftereachiteration.
for(intx=5;x>0;x—)
xstartsatfiveandisdecrementedbyoneeachtimeaslongasthevalueofxdoesnotgobelowone.
The three fields in a for loop are optional. They can be left empty, but the semicoloncannotbeomitted.Forexample:
for (;x<5;) is a loopwith an initializationor an increase and is equivalent to awhileloop.
for (;x<5;++x) is a loopwith increase but no initialization. In this case the variablemighthavebeeninitializedalreadyelsewhereintheprogram.
for(x=5;;++x)isaloopwithnocondition.Thus,itisthesameasaloopwithtrueascondition.Thusresultinganinfinitelooporendlessloop.
#include<iostream>
usingnamespacestd;
intmain()
{
for(intn=5;n>0;n—){
cout<<n<<“,”;
}
cout<<“Endofline\n”;}}
Itproducesthesameresult-5,4,3,2,1,Endofline.
3.3JumpstatementsJump statements allow altering the flow of a program by performing jumps to specificlocations.There are three typesof jump statements.Theyarebreak, continue andgoto.Letuslookatanexample:
Thecontinuestatement
The continue statement causes the program to skip the rest of the loop in the currentiterationisiftheendoftheblockhasbeenreachedcausingittojumptothestartofthefollowingiteration.Thenumber3isskipped.
for(intx=5;x>0;x—){
if(x==3)continue;
cout<<x<<“,”;
}
cout<<“Numberskipped\n”;}
ThegotostatementGotoallowsanabsolutejumptoanotherpointintheprogram.Itusesalabelwitha:
#include<iostream>
usingnamespacestd;
intmain()
{
inta=10;
LOOP:do
{
if(a==15)
{
a=a+1;
gotoLOOP;
}
cout<<“valueofa:”<<a<<endl;
a=a+1;
}while(a<20);
return0;
}
Heretheoutputwouldbealistofnumbersfrom10to19withoutthenumber15.Hereweseeadowhileloop.Thenumbercountsfrom10to19butskips15.
3.4Switch
switch(expression)
{
caseconstant1:
groupofstatements-1;
break;
caseconstant2:
groupofstatements-2;
break;
.
default:
defaultgroupofstatements
}
Switchevaluatesexpressionandchecksifitisequivalenttoconstant1.Ifitis,itexecutesthegroupofstatements-1untilitreachesthebreakstatement.Atthebreakstatement,theprogramjumpstotheendoftheentireswitchstatement–theclosingbrace.
If expression is not equal to constant1, it then checks against constant2 and if equalexecutesthegroupofstatements-2untilabreakisfoundandthenjumpstotheendoftheswitchstatement.
Finally, if the value of the expression did notmatch any of the constants the programexecutesthestatementsincludedafterthedefault:labelifitexists.
Letuslookatanexample:
#include<iostream>
usingnamespacestd;
intmain()
{
charx=‘C’;
switch(x)
{
case‘A’:
cout<<“Sedan”<<endl;
break;
case‘B’:
cout<<“MiniVan”<<endl;
break;
case‘C’:
cout<<“Truck”<<endl;
break;
default:
cout<<“Invalidentry”<<endl;
}
cout<<“Yourselectionis”<<x<<endl;
return0;
}
Theoutputwillbe:Truck
YourselectionisC
IfanythingotherthanA,B,Cisenteredthedefaultmessagewillbedisplayedwhichisinvalidentry.
4Functions
“Everytruthhasfourcorners:asateacherIgiveyouonecorner,anditisforyoutofindtheotherthree.”—Confucius
4.0DefinitionofafunctionAfunctionisasetofstatementsthattogetherperformatask.
Afunctionhasafunction’sname,returntype,andparameters.TherecanbemorethanonefunctiondeclarationinaC++program.
Thegeneralsyntaxofafunctionisasfollows:
return_typefunction_name(parameterlist)
{
body
}
• ReturnType:Thereturn_typeisthedatatypeofthevaluethefunctionreturns.Iffunctionsdonoreturn,avaluethereturn_typeissettovoid.
• FunctionName:Thisistheactualnameofthefunction.Thefunctionnameandtheparameterlisttogetherconstitutethefunctionsignature.
• Parameters:When a function is invoked, you pass a value to the parameter.Thisvalueisreferredtoasactualparameterorargument.Theparameterlistreferstothetype,order,andnumberoftheparametersofafunction.Afunctionmaycontainnoparameters.
• FunctionBody: The function body contains a collection of statements that definewhatthefunctiondoes.
Letuslookatanexample:
//functionexample
#include<iostream>
usingnamespacestd;
intmultiply(intx,inty)
{
intz;
z=x*y;
returnz;
}
intmain()
{
intw;
w=multiply(5,2);
cout<<“Theresultis”<<w;
}
Here is a function,multiply that has been defined outside themain function. Inside themainfunctionwehavecalledthefunctionbyitsnamemultiplyandpassedtoittwovalues5and2.Thevalueswillbeassignedtox=5andy=2.Theresultwillbe10.
Remember the function is called frommain.At this point, activity is transferred to thefunction and once the function has been executed, control returns to the point inmainwherethefunctionwascalled.
Ifonelooksatthemultiplyfunctionitreturnsavaluezbacktomainwhichisofthesametypeasw.Thevalueofwwillbeprintedwith thevalueofz computed in the functionblock.
Afunctioncanbecalledseveraltimesinsideamainfunction.
4.1FunctionsthatdonotreturnavalueLetuslookatthefollowingexample:
//voidfunctionexample
#include<iostream>
usingnamespacestd;
voidpmessage()
{
cout<<“HelloIamfunction!”;
}
intmain()
{
pmessage();
}
Inthisexample,wearecallingafunctionfrommain.ItwillprintthemessageHelloIamafunction!
Unlikethepreviousexampleinsection,4.0novaluesaretransferredtothefunctionandnonearecomputedandreturned.
Whilemostfunctionsusethecallbyvaluemethodasinthepreviousexample,theuseof
voidtermindefiningfunctionpmessagetellsthatthefunctiondoesnotreturnavalue.
Furthernotetherearenoparametersinthebracketofthepmessagefunction.Theabsenceof theseparametersmeans that the function isnotgoing to receiveanyvalues from themainfunction.
Iftheexecutionofmainendsnormallywithoutencounteringareturn(return0;)statementthecompilerassumesthefunction,endswithanimplicitreturnstatement.
Allotherfunctionswithareturntypeshallendwithaproperreturnstatementthatincludesareturnvalue.
Therecanbemanyfunctions inaC++programbut themain()functionmustalwaysbethereirrespectiveofhowcomplicatedtheprogramis.
4.2Defaultvaluesforparameters
When you define a function, you can specify a default value for each of the lastparameters. This value is used if the corresponding argument is left blank when thefunctioniscalled.
Letuslookatthefollowingexample:
//defaultvaluesinfunctions
#include<iostream>
usingnamespacestd;
intdivide(intx,inty=5)
{
intz;
z=x/y;
return(z);
}
intmain()
{
cout<<divide(10)<<‘\n’;
cout<<divide(30,6)<<‘\n’;
return0;
}
Hereinthefirstcalldivide(10)thevaluestransferredtoxis10andsincethereisnothingelsetransferred10willbedividedbyy=5resultingintheanswer2.
In the secondcall divide (30, 6), functionparametersxwill take thevalueof30 andywhosevalueinthefunctionis5willgetthevalue6.Thus,theresultwillbe5.
5Arrays
“Readnottocontradictandconfute,nortobelieveandtakeforgranted…buttoweighandconsider.”—FrancisBacon
5.0WhatareArraysAnarray,storesafixed-sizesequentialcollectionofelementsofthesametype.Anarrayisused to store a collection of data, but it is oftenmore useful to think of an array as acollectionofvariablesofthesametype.
Allarraysconsistofcontiguousmemorylocations.Thelowestaddresscorrespondstothefirstelementandthehighestaddresstothelastelement.Theindexvalue0representthelowestaddress.
5.1SimpleArraysdoubleamount[5]={1000,800,900,700,600}
Thenumberoftheelementsofthecurlybracket{}mustnotbemorethanthenumberin[]brackets.Thisisasingleorone-dimensionalarray.
Ifthenumberin[]bracketsismissingthenanarrayofjustenoughsizetoaccommodatetheelementswillbecreated.
Ifwewriteamount[4]=600thiswouldmeanthatthe5thplaceor4th indexonthearraywillhavethevalueof600.
0 1 2 3 4
1000 800 900 700 600
AmountSoasshown5cellsnumbered0through4.
Thefifthpositionrepresentedbyindex4willholdthevalueof600inaone-dimensionalarray.
5.2AccessinganelementofanarrayStoringvalues isanarray isonlygoodifwecanaccess them.Toaccesselementsofanarraywecanusealoopsuchasa-forloop.
//arraysexample
#include<iostream>
usingnamespacestd;
intamount[]={16,2,77,40,12071};
intn;
intv=0;
intmain()
{
for(n=0;n<5;++n)
{
v=v+amount[n];
}
cout<<v;
return0;
}
Thiswillgivethesumofthefivenumbersinthearray,whichwillbe12206.
5.3Multi-dimensionalArraysTheformatforamultidimensionalarrayisasfollows:
typename[size1][size2]…[sizen];
Thesimplestformofthemultidimensionalarrayisthetwo-dimensionalarray.Todeclareatwo-dimensionalintegerarrayofsizex,y,youwouldwritesomethingasfollows:
typearrayname[x][y];
WheretypecanbeanyvalidC++datatypeandarraynamewillbeavalidC++identifier.
inta[2][3]isanarraywithtworowsandthreecolumns.Forexample:
inta[2][3]={
{0,1,2},
{3,4,5}
};
Sohere,therow1hastheindex0orinsimplewords,wecountrowsstartingwith0andnot1.Thustherownumberfortheabovearrayis0&1andcolumnnumbersare0…2.
Column0 Column1 Column2
Row0 0 1 2
Row1 3 4 5
Nowweaccesstheelementsofamulti-dimensionalarrayinthesamemanneraswedidforasinglearraybyusingaloop.Letusconsiderafourrowtwocolumnarraydefinedby
a[4][2].Letusassigntoitthefollowingvalues:
a[4][2]={{0,0},{1,2},{2,4},{3,6}}
Toprintoutthevaluesofthisandsimilararrayswewillusethe‘for’loop.Thekeyloopwouldbe:
for(inti=0;i<4;i++)
for(intj=0;j<2;j++)
{
cout<<“a[”<<i<<“][”<<j<<“]:”;
cout<<a[i][j]<<endl;
}
Herewehavei<4becauseweknowthecolumnsarenumbered0through3.
Hereisthefullcode:
#include<iostream>
usingnamespacestd;
intmain()
{
//anarraywith3rowsand2columns.
inta[3][2]={{0,0},{1,2},{2,4}};
//outputeacharrayelement’svalue
for(inti=0;i<3;i++)
for(intj=0;j<2;j++)
{
cout<<“a[”<<i<<“][”<<j<<“]:”;
cout<<a[i][j]<<endl;
}
return0;
}
Theoutputwouldbesimilartothis:
a[0][0]:0
a[0][1]:0
a[1][0]:1
a[1][1]:2
a[2][0]:2
a[2][1]:4
6Pointers
“Teachingstudentstocountisfine,butteachingthemwhatcountsisbest.”
—BobTalber
6.0WhatarePointersApointerisavariablewhosevalueistheaddressofanothervariable.Letuslookatthefollowingexample:
#include<iostream>
usingnamespacestd;
intmain()
{
intx;
cout<<“Addressofxvariable:”;
cout<<&x<<endl;
return0;
}
Theoutputofthiscodewillbesimilartothis:
Addressofxvariable:0031FDE0
Addressofyvariable:0031FDCC
Whatweseeaboveisthememorylocationforvariablesx.Noticethatthe‘&’isusedtogivethememorylocation.
Thisvaluewillvaryandmaybedifferentonyourcomputer.However,whatisimportanttounderstandtokeepinmindisthattheyarememoryaddresses.
Wecandefinepointersbyfirstindicatingitstypeasfollows:
int*x;
float*y;
double*p;
char*w
Thesepointerswillpointtoaninteger,float,doubleandcharrespectively.
Wecanstorethevalueofvariableinapointerandtheaddressofthevariable.Letuslook
atthefollowingexample:
#include<iostream>
usingnamespacestd;
intmain()
{
intx=10;
int*ip;//pointervariable
ip=&x;//storeaddressofvarinpointervariable
cout<<“Valueofxvariable:”;
cout<<x<<endl;
cout<<“Addressstoredinipvariable:”;
cout<<ip<<endl;
cout<<“Valueof*ipvariable:”;
cout<<*ip<<endl;
return0;
}
Theoutputwillbesimilartothis:
Valueofxvariable:10
Addressstoredinipvariable:002BFC90
Valueof*ipvariable:10
6.1PointerconceptsLetuslookatsomepointerconcepts:
• Nullpointers
#include<iostream>
usingnamespacestd;
intmain()
{
int*p=NULL;
cout<<“Thevalueofpis”<<p;
return0;
}
ThisisanexampleofaNULLpointer.Theoutputofthiscodeis:
Thevalueofpis0
• PointerArithmetic
Apointerisanaddress,whichisanumericvalue;therefore,youcanperformarithmeticoperationsonapointerjustasyoucananumericvalue.Fourarithmeticoperatorsthatcanbeusedonpointers:++,—,+,and–.
For the following example, we will define an array y of three elements. It is a singledimensionarray.Wewilluseapointery topoint to thearrayy.Letusassumeboth thepointerandthearrayareoftypeinteger.
Wewill thena looptogothrougheachelementof thearrayyandprintout itsmemoryaddressandvalue.Wepreferusingapointer intheprograminsteadofanarraybecausethe variable pointer can be incremented, unlike the array name, which cannot beincrementedbecauseitisaconstantpointer.
Aforloopisusedinthisexampletogothrougheachelementofthearrayyaswasdoneinthechapteronarrays.
Letusthelookattheexample:
#include<iostream>
usingnamespacestd;
constintx=3;
intmain()
{
inty[x]={100,200,300};
int*p;
//letushavearrayaddressinpointer.
p=y;
for(inti=0;i<x;i++)
{
cout<<“Addressofy[”<<i<<“]=”;
cout<<p<<endl;
cout<<“Valueofy[”<<i<<“]=”;
cout<<*p<<endl;
p++;
}
return0;
}
Theexpectedoutputofthecodeissimilarto:
Addressofy[0]=0031FD88
Valueofy[0]=100
Addressofy[1]=0031FD8C
Valueofy[1]=200
Addressofy[2]=0031FD90
Valueofy[2]=300
• Pointerversusarrays
Pointersandarraysarestronglyrelated.Apointerthatpointstothebeginningofanarraycanaccessthatarraybyusingeitherpointerarithmeticorarray-styleindexing.Letuslookatthefollowing:
#include<iostream>
usingnamespacestd;
constintx=3;
intmain()
{
inty[x]={100,200,300};
int*p;
//letushavearrayaddressinpointer.
p=y;
for(inti=0;i<x;i++)
{
cout<<“Addressofy[”<<i<<“]=”;
cout<<p<<endl;
cout<<“Valueofy[”<<i<<“]=”;
cout<<*p<<endl;
//pointtothenextlocation
p++;
}
return0;
}
Theoutputoftheprogramwouldbesimilarto:
Addressofy[0]=004DF750
Valueofy[0]=100
Addressofy[1]=004DF754
Valueofy[1]=200
Addressofy[2]=004DF758
Valueofy[2]=300
Ifweusethearraynameyandwritethisy++thatissyntacticallywrong.
7Strings
“Educationisnottoreformstudentsoramusethemortomakethemexperttechnicians.Itistounsettletheirminds,widentheirhorizons,inflametheirintellects,teachthemtothinkstraight,ifpossible.”—RobertM.Hutchins
7.0CharacterStringWearefamiliarwiththechardatatype.Wealsohavegonethrougharraysandpointersinpreviouschapters.
LetusthereforelookatthefollowingcodewherewedefineacharacterarraytoprintthewordYes.
#include<iostream>
usingnamespacestd;
intmain()
{
charx[3]={‘Y’,‘e’,‘s’,‘\0’};
cout<<x<<endl;
return0;
}
Theexpectedoutputofthisprogramis:
Yes
Here thedeclarationcharx [3] isaone-dimensionalarrayofcharacters terminatedbyanullcharacter‘\0’.TheC++compilerautomaticallyplacesthe‘\0’attheendofthestringwhenitinitializesthearray.
7.1StringFunctionsSomeofthecommonstringfunctionsinC++are:
No FunctionName Description
1 strcpy(s1,s2) Copiesstrings2intostrings1
2 strcat(s1,s2) Concatenatesstrings2ontotheendofstring1
3 strlen(s1) Returnsthelengthofstrings1
4 strcmp(s1,s2) Returns0ifs1ands2arethesame;lessthan0ifs1<s2;greaterthan0ifs1>s2.
include<iostream>
#include<string>
usingnamespacestd;
intmain()
{
charx[10]=“Hello”;
chary[10]=“World”;
strcat(x,y);
cout<<“strcat(x,y):”<<x<<endl;
return0;}
TheoutputwillbeHelloWorld.Justkeepaneyeonthesizeofthearraysxandy.
8References
“Education…ispainful,continualanddifficultworktobedoneinkindness,bywatching,bywarning,…
bypraise,butaboveall—byexample.”—JohnRuskin
8.0WhatareReferencesA reference variable is an alias, that is, another name for an already existing variable.TherecannotbeNULLreferencesandreferencesmustbe tovalidvariables.Referencesinitializedtoanobjectcannotrefertoanotherobject.Referencesmustbeinitializedwhentheyarecreated.
include<iostream>
usingnamespacestd;
intmain()
{
intx;
//declarereferencevariable
int&y=x;
x=10;
cout<<“Valueofx:”<<x<<endl;
cout<<“Valueofyreference:”<<y<<endl;
return0;}
Expectedoutputofthisexampleis:
Valueofx:10
Valueofyreference:10
9File
“TellmeandIforget.TeachmeandIremember.InvolvemeandIlearn.”—BenjaminFranklin
9.0InputandoutputwithfilesSofar,wehaveusedcinandcoutasinputandoutputfortheprogramswehavewritten.Nowlookuslookathowtodealwithexternalfiles.C++providesthefollowingclassestoachievethis.Itrequirestheuseofanewadditionalheaderotherthaniostream.Theheaderisfstream.
Stream Description
ofstream Towritetofiles
ifstream Toreadfromfiles
fstream Toreadandwritefromandintofiles
Letuslookatanexample:
//basicfileoperations
#include<iostream>
#include<fstream>
usingnamespacestd;
intmain(){
ofstreammyfile;
myfile.open(“first.txt”);
myfile<<“Hello!Iamwritingtoafile.\n”;
myfile.close();
return0;}
Thiswritestoatextfileknownasfirst.txt.ThewordsHello!Iamwritingtoafile.Ifthefilefirst.txtdoesnotexist itwillcreatedaslongaspermissionsonyourcomputerallowforit.Otherwise,createthefilefirstnotingthedirectoryofC++compiler.
9.1OpeningafileInordertoopenafilewithastreamobjectweusethefollowingsyntax:
open(filename,mode);
Wherefilenameisastringrepresentingthenameofthefiletobeopened,andmodeisanoptionalparameterwithacombinationofthefollowingflags:
Flags Description
ios::in Openforinputoperations.
ios::out Openforoutputoperations.
ios::binary Openinbinarymode.
ios::ate Settheinitialpositionattheendofthefile.Ifthisflagisnotset,theinitialpositionisthebeginningofthefile.
ios::app Alloutputoperationsareperformedattheendofthefile,appendingthecontenttothecurrentcontentofthefile.
ios::trunc Ifthefileisopenedforoutputoperationsanditalreadyexisted,itspreviouscontentisdeletedandreplacedbythenewone.
All these flags can be combined using the bitwise operatorOR (|). For example, ifwewanttoopenthefilefirst.bininbinarymodetoadddatawecoulddoitbythefollowingcalltomemberfunctionopen:
ofstreammyfile;
myfile.open(“first.bin”,ios::out|ios::app|ios::binary);
Eachoftheopenmemberfunctionsofclassesofstream,ifstreamandfstreamhasadefaultmodethatisusedifthefileisopenedwithoutasecondargument:
Stream DefaultMode
ofstream ios::out
ifstream ios::in
Fstream ios::in|ios::out
Tocheckifafilestreamwassuccessfulinopeningafile,onecanusetheis_openmember.Thesyntaxwouldlooklikethis:
if(first.isopen()){statements}
9.2ClosingafileWhenwearefinishedwithwritingtoafileorreadingfromitwehavetoclosethefile.
Thesyntaxforthatisasfollows:
first.close();
9.3TextFilesTextfilesarethosewheretheios::binaryflagisnotincludedintheiropeningmode.Theyhavetheextentions.dat,.txt,.csvetc.
#include<iostream>
#include<fstream>
usingnamespacestd;
intmain(){
ofstreammyfile(“first.txt”);
if(myfile.is_open())
{
myfile<<“Thisisaline.\n”;
myfile<<“Thisisanotherline.\n”;
myfile.close();
}elsecout<<“Unabletoopenfile”;
return0;}}
//readingatextfile
#include<iostream>
#include<fstream>
#include<string>
usingnamespacestd;
intmain(){
stringline;
ifstreammyfile(“first.txt”);
if(myfile.is_open())
{
while(getline(myfile,line))
{
cout<<line<<‘\n’;
}
myfile.close();
}
elsecout<<“Unabletoopenfile”;
return0;}}}
Thisprogramallowsonetoreadfromatextfile.
10StorageClasses
“Alwaystoseethegeneralintheparticularistheveryfoundationofgenius.”—ArthurSchopenhauer
10.0TypesofstorageclassesLetuslookatfivestorageclasses:
• auto• register• static• extern• mutable
Theautostorageclassisthedefaultstorageclassforalllocalvariables.
{
inty;
autointx;
}
Theautostorageclasscanonlybeusedwithinfunctions.TheregisterstorageclassisusedtodefinelocalvariablesthatshouldbestoredintheregisterratherthanRAM.
{
registerintx;
}
Theregistershouldonlybeusedforvariablesthatrequirequickaccesssuchascounters.
Thestaticstorageclassinstructsthecompilertokeepalocalvariableinexistenceduringthe lifetimeof theprograminsteadofcreatinganddestroying iteach timeitcomes intoandgoesoutofscope.
Therefore, making local variables static allows them to maintain their values betweenfunctioncalls.Thestaticmodifiermaybeappliedtoglobalvariables
#include<iostream>
usingnamepacestd;
voidy(void);
staticintcount=5;/*Globalvariable*/
intmain()
{
while(count—)
{
y();
}
return0;
}
//Functiondefinition
voidy(void)
{
staticintx=0;//localstaticvariable
x++;
std::cout<<“xis”<<x;
std::cout<<“andcountis”<<count<<std::endl;
}
Theexpectedoutputfortheaboveexampleisasfollows:
xis1andcountis4
xis2andcountis3
xis3andcountis3
xis4andcountis1
xis5andcountis0
Theexternstorage class gives a reference of a global variable that is visible to all theprogramfiles.Whenthisclassisusedvariablescannotbeinitialized.
#include<iostream>
intcount;
externvoidw();
main()
{
count=5;
w();
}
Letusassumethecodeaboveisinafilecallfirst.cpp.Letalsoassumethereisasecondfilecalledsecond.cpp
#include<iostream>
Externintcount;
voidw(void)
{
std::cout<<“Countis”<<count<<std::endl;
}
Sincethefunctionwasdeclared,withexternitisavailabletothesecondfileanditisabletoprintthevalueofcountas5.Themutablemembercanbemodifiedbyaconstmemberfunction.
11Classes
“Therearetwokindsofteachers:thekindthatfillsyouwithsomuchquailshotthatyoucan’tmove,andthekindthatjustgivesyoualittleprodbehindandyou
jumptotheskies.”—RobertFrost
11.0BuildingclassesClasses form one of the fundamental features that enableC++ to be an object orientedlanguage.
Aclassdefinitionstartswiththekeywordclassfollowedbytheclassname;andtheclassbody,enclosedbyapairofcurlybraces.Eitherasemicolonoralistofdeclarationsmustfollowaclassdefinition.
Letuslookatanexampleofaclass.
classCar
{
public:
doublelength//Lengthofthecar
doublewidth;//Widthofthecar
doubleweight;//Weightofthecar
doubleengine;//Enginesize
};
We have defined a class known as car with a few features attributed to the car. Thekeywordpublicdeterminestheaccessattributesofthemembersoftheclassthatfollowit.Apublicmembercanbeaccessedfromoutsidetheclassanywherewithinthescopeoftheclassobject.
Nowletuslookatobjects.
Letusassumetherearetwocars–car1andcar2.Wewilldeclareitasfollows:
Carcar1
Carcar2
Bothobjectswillnowhaveacopyof thedatamembersof theclassknownasCar.Forexample:
#include<iostream>
usingnamespacestd;
classCar
{
public:
doublelength;//Lengthofthecar
doublewidth;//Widthofthecar
doubleweight;//Weightofthecar
doubleengine;//Enginesize
};
intmain()
{
Carcar1;//Declarecar1oftypeCar
Carcar2;//Declarecar2oftypeCar
car1.weight=1500;
car1.engine=1400;
car2.weight=2000;
car2.engine=1800;
cout<<“Weightofcar1:”<<car1.weight<<endl;
cout<<“Weightofcar2:”<<car2.weight<<endl;
return0;
}
Theoutputofthecodeabovewouldbe:
Weightofcar1:1500
Weightofcar2:2000
11.1Classconcepts• Classmemberfunction
Amemberfunctionofaclassisafunctionthathasitsdefinitionwithintheclassdefinitionlikeanyothervariable.Itoperatesonanyobjectoftheclassofwhichitisamember,andhasaccesstoallthemembersofaclassforthatobject.Letuslookatanexample:
classMarks
{
public:
doubleprelim;//narksinfirstexam
doublemidterm;//marksinsecondexam
doublefinal;//marksinfinalexam
doublegetfinal(void)
{
return(0.3*prelim)+(0.3*midterm)+(0.4*final);
}
};
Herethefunctiongetfinal()hasbeendefinedwithintheclass.Ifthefunctionisnotdefinedwithintheclassthenusescoperesolutionoperator,::,asfollows:
• Classmodifiers
DatahidingisoneoftheimportantfeaturesofObjectOrientedProgramming(OOP).Theaccess labels - public, private, and protected, specify the access restriction to the classmembers.
Apublicmemberisaccessiblefromanywhereoutsidetheclassbutwithinaprogram.Aprivatemembervariableorfunctioncannotbeaccessed,fromoutsidetheclass.Onlytheclassandfriendfunctionscanaccessprivatemembers.Letuslookatthis:
#include<iostream>
usingnamespacestd;
classCar
{
public:
doublelength;
voidsetw(doublew);
doublegetw(void);
private:
doubleweight;
};
//Memberfunctionsdefinitions
doubleCar::getw(void)
{
returnweight;
}
voidCar::setw(doublew)
{
weight=w;
}
intmain()
{
Carcar1;
car1.length=1100;//OK:becauselengthispublic
cout<<“Lengthofcar:”<<car1.length<<endl;
//car1.weight=1500;//Error:becauseweightisprivate
car1.setw(1500);//Usememberfunctiontosetit.
cout<<“Weightofcar:”<<car1.getw()<<endl;
return0;}
Herethedeclarationofweightasbeingprivateresultedincar1,whichisanobjectofCarfrombeingabletoaccesstheweightdirectly.Theoutputofthisprogramwouldbe:
Lengthofcar:1100
Weightofcar:1500
Aprotectedmembervariableorfunctionisverysimilartoaprivatemember.Theycanbeaccessedinchildclasses,whicharecalledderivedclasses.
#include<iostream>
usingnamespacestd;
classCar
{
protected:
doubleweight;
};
classSmallcar:Car//Smallcaristhederivedclass.
{
public:
voidsetSmallw(doublewid);
doublegetSmallw(void);
};
doubleSmallcar::getSmallw(void)
{
returnweight;
}
voidSmallcar::setSmallw(doublew)
{
weight=w;
}
intmain()
{
Smallcarcar1;
car1.setSmallw(1500);
cout<<“Weightofcar:“<<car1.getSmallw()<<endl;
return0;
}
Theoutputoftheprogramwouldbe:
Weightofcar:1500
• Constuctors
Aclassconstructorisaspecialmemberfunctionofaclassthatisexecutedwheneverwecreatenewobjectsofthatclass.
Aconstructorwillhaveexactsamenameastheclassanditdoesnothaveanyreturntypeatall,notevenvoid.Letuslookatthefollowing:
#include<iostream>
usingnamespacestd;
classCar
{
public:
voidsetw(doublew);
doublegetw(void);
Car();//Thisistheconstructor
private:
doubleweight;
};
//Memberfunctionsdefinitionsincludingconstructor
Car::Car(void)
{
cout<<“Pleasewait!Answerisontheway”<<endl;
}
doubleCar::getw(void)
{
returnweight;
}
voidCar::setw(doublew)
{
weight=w;
}
intmain()
{
Carcar1;
car1.setw(1500);
cout<<“Weightofcar:”<<car1.getw()<<endl;
return0;}
Heretheoutputwouldbetheweightofthecar.Thedifferenceis:
Pleasewait!Answerisontheway
Weightofcar:1500
• Destructors
#include<iostream>
usingnamespacestd;
classCar
{
public:
voidsetw(doublew);
doublegetw(void);
Car();//Thisistheconstructordeclaration
~Car();//Thisisthedestructor:declaration
private:
doubleweight;
};
//Memberfunctionsdefinitionsincludingconstructor
Car::Car(void)
{
cout<<“Objectisbeingcreated”<<endl;
}
Car::~Car(void)
{
cout<<“Objectisbeingdeleted”<<endl;
}
doubleCar::getw(void)
{
returnweight;
}
voidCar::setw(doublew)
{
weight=w;
}
intmain()
{
Carcar1;
car1.setw(1500);
cout<<“Weightofthevehicle:”<<car1.getw()<<endl;
return0;
}
Theexpectedoutputis:
Objectisbeingdeleted
Theweightofthevehicle:1500
12Inheritance
“Staycommittedtoyourdecisions;butstayflexibleinyourapproach.”—TonyRobbins
12.0TheconceptofInheritanceAclasscanbederivedfrommore thanoneclasses,whichmeans itcan inheritdataandfunctionsfrommultiplebaseclasses.Todefineaderivedclass,weuseaclassderivationlisttospecifythebaseclass(
Letus lookat anexampleby firstwritingabaseclass.Here thebaseclass thatwearegoingtodefineiscalledvehicle.Thevehiclehascertainpropertiessuchaslength,width,weight,engineetc.
Wewillthencreateaderivedclasscalledcar.Asacarisavehicleanditwillinheritthepropertiesofthebaseclassthatisvehicle.
Theexampleisasfollows:
#include<iostream>
usingnamespacestd;
//Baseclass
classvehicle
{
public:
voidsetengine(doublee)
{
engine=e;
}
public:doublegetengine()
{
return(engine);
}
protected:
doubleweight;
doubleengine;
};
//Derivedclass
classcar:publicvehicle
{
};
intmain(void)
{
vehiclecar;
car.setengine(1500);
cout<<“Engine:”<<car.getengine()<<endl;
return0;
}
The output is 1500. Inheritance is a key element as to why C++ is an object-orientedlanguage.
12.1SomeOOP’stermsPolymorphismisaterminC++.Thisfeaturemeansthatthereareahierarchyofclasses,whicharerelatedtoeachotherthroughinheritance.Polymorphismcanresultinacalltoafunction being replied to by another function depending on the object that called thefunction.
Placingavirtualfunctioninthebaseclasswilldealwithpolymorphism.
Dataabstractionmeansshowingonlynecessary informationandhidinganybackgrounddetails.Encapsulation isa feature thatkeepsdataand functions thatoperateon thedatasaferfromexternalmisuse.
Any C++ program, which has public and private members, is an example of dataencapsulationanddataabstraction.Forexample:
classCar
{
public:
doublegetw(void)
{
returnweight;
}
private:
doubleweight;
}
13Exceptions
“Alwaystoseethegeneralintheparticularistheveryfoundationofgenius.”—ArthurSchopenhauer
13.0ErrorhandlingAnexceptionisdefinedasaproblemthathappenswhenaprogramisrunning.Exceptionsprovideaway to transfercontrol fromonepartofaprogramtoanother.C++exceptionhandlingisbuiltuponthreekeywords:try,catch,andthrow.
try
{
//protectedcode
}catch(ExceptionNamea1)
{
//catchblock
}catch(ExceptionNamea2)
{
//catchblock
}catch(ExceptionNamean)
{
//catchblock
}
Exceptions can be introduced anywhere a bunch of statements are being executed. Forexample:
#include<iostream>
usingnamespacestd;
doubledivision(intv,intw)
{
if(w==0)
{
throw“Divisionbyzero”;
}
return(v/w);
}
intmain()
{
intx=10;
inty=0;
doublez=0;
try{
z=division(x,y);
cout<<z<<endl;
}catch(constchar*msg){
cerr<<msg<<endl;
}
return0;
}
14Conclusion
TheC++languageisaveryversatileprogrammingtool.
ThepreviouschaptersconcentratedoncreatingthebasicbuildingblocksofastandaloneC++ program. Chapters 11 and 12 introduced topics important to object orientedprogramming. As you go on tomore advanced programming youwill encounter otherOOP’sconceptssuchaspolymorphism,encapsulation,dataabstractionanddatahidingindetail.
Interestinglyintheexampleswehavedone,someoftheseconceptsarealreadypresent.
From thispoint, onecould takeamoreadvanced lookatC++programmingkeeping inmindthatwideusageofthislanguage.
Ifyouneed,thezipfileofalltheprogramsinthechaptersthatwehavedoneorupdatesonthissubjectandsubsequentandrelatedtopicsvisithttp://beam.to/fjtbooks
