The First ECE250 Tutorial C++andClasses

TiuleyAlguindigue(LabInstructor)Winter2020

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Outline: The First ECE250 Tutorial

•  ReviewObjectOrientedProgramingü Classes–Userdefinedtypesü ClassDesign–UMLnotation

•  ReviewC++ü C++arraysü Pointersü Dynamicmemoryallocationü Constructorsü Destructorü Parameterpassingü Overloadingoperators

•  DesignandimplementaC++classü Hands-onExample:APolynomialClass

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Hands-on Example: Polynomial Definition

•  Expressionconsistingofvariablesandcoefficientswithnon-negativeintegerexponents

• Ourexampleconsidersthesinglevariablepolynomial(x)

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C++ Background

Question1:intx;//thetypeofxisintPolynomialp1;//p1isan______,aninstanceof______________Question2:p1.setPolynomial(3,10.0,20.0,30.0)p1.evaluate(2.0);p1.print();setPolynomial,evaluateandprintare______________implementedbyclass__________

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Example – Class Design

• ClassDiagram–UniversalModelingLanguage(UML)

Polynomial

size:integercoeff[]:double

evaluate():doubleadd(q:Polynomial):Polynomialdiff(q:Polynomial):Polynomialmult(q:Polynomial):Polynomialprint():void

Attributes(membervariablesinC++)

Operationsormethods(memberfunctionsinC++)

Classname

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Design Document

•  Seesampledocumentprovided(talguind_design_p0.pdf)•  Followthisformatforprojects0-4

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Polynomial class Example – A first version

Polynomialclass•  Membervariables

ü Arraytorepresentpolynomialie.20.0*X+30.0*X**2,representedasP={0.0,20.0,30.0}

ü Sizeofarray(degree+1)ie.size=3inthisexample

•  Memberfunctionsü Constructorsü Destructorü addü printü Operators(+,=)

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Constructor function

•  “Specialfunctionwhichisautomaticallycalledwheneveranewobjectofaclassiscreated,allowingtheclasstoinitializemembervariablesorallocatestorage”

http://www.cplusplus.com/doc/tutorial/classes/• Declaredjustlikearegularmemberfunction,butwithanamethatmatchestheclassnameandwithoutanyreturntype.

Polynomial(const int& size_p, const double coeff_p[]);

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Destructor function

•  “Destructorsfulfilltheoppositefunctionalityofconstructors:theyareresponsibleforthenecessarycleanupneededbyaclasswhenitslifetimeends.”http://www.cplusplus.com/doc/tutorial/classes2/

• Namedthesameastheclass,precededby~~Polynomial();

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Dynamic Memory Allocation

•  Thenumberofelementsinthearraythatrepresentsthepolynomialdependsonthedegreeofthepolynomialdouble *coeff; // pointer to array int size ; // degree + 1

• coeff is a pointer to the start of an array that will be dynamically allocated so that it can store “size” elements

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Dynamic Memory Allocation

• WhenaPolynomialobjectiscreated–theconstructorfunctioniscalledtoallocateresourcesandinitializetheobject.Inthisfunctionwerequestmemoryforanarray,with“size” elements,eachanumberoftypedouble.

coeff = new double[size];•  Inthedestructorfunction,invokedwhenthelifetimeoftheobjectends,wereleasethememorythatwasallocatedforthisobject

delete [] coeff ;

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Exercise 1(10 min) •  LogintoLEARN,findtheECE250course,anddownloadtoyourlaptopsthefilesfoundunder“Content”,folder“Tutorials”|”Tutorial1”ü  Polynomial.h–Polynomialclassinterface(declarations)ü Polynomial.cpp–Polynomialclassimplementationü  polynomialtest.cpp-Testprogramwithmain()function

•  Examinethesefiles,notedownquestionsyouhave.•  Compileandexecutethetestprogram

ü youcanuseanIDE.ü InUNIXlikeenvironmentyouwouldtypethecommands:

g++polynomialtest.cppPolynomial.cpp–opolynomialtest./polynomialtest

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What questions do you have?

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Question: ConsiderwhatwillchangeintheprovidedimplementationifthePolynomialhadbeenimplementedasa“struct”insteadofa“class”Inthiscoursewewillfavortheuseofclassesvsstructs.Wewillpracticeobject-orientedprogramming,creatingobjectsthatcontainbothdataandmethods.

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Using the Polynomial class – a start

// Declaring, initializing, adding two arrays and printing polynomialint main() {

double p1_array[] = {0.0,1.0,3.0};Polynomial p1(3,p1_array); // 3 -terms - 0 + X + 3X**2

Polynomial p1copy(p1); // p1copy is a copy of p1Polynomial p2copy = p2 ; // p2 is copied to p2copy

Polynomial p3;p3 = p1.add(p2); // p3 = p1 + p2p3.print();

}

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Access Specifiers in C++

Protecting data members and providing services in your class private–usedfordatamemberspublic –usedformemberfunctions

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Polynomial.h – class interface

class Polynomial {

// member variables

private:

double *coeff; // array of coefficients

int size ; // size = degree + 1

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Polynomial.h – class interface

// member functions public:

Polynomial (const int& size_p, const double coeff_p[]);

Polynomial();

Polynomial (const Polynomial &polynomial_to_copy);

~Polynomial();

Polynomial add( const Polynomial& right) const ;

void print();

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Polynomial class – member functions

Definingfunctionparameters Polynomial add(const Polynomial& right ) const ; Questions: Why the passing by reference - using & ? What will the “const” keyword for the parameter?

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Polynomial class - member functions

constmemberfunction Polynomial add( const Polynomial& right) const ;

Question: Why the const keyword for the function declaration?

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First Constructor Thefirstconstructor–takesarrayandarraysizeasparameter

Polynomial::Polynomial (const int& ni, const double ci[]){ size = ni; coeff = new double[size]; for(int i = 0; i < size; i++){ coeff[i] = ci[i]; }

}

Precededbyclassname

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Arraysarepassedbyreference

Second Constructor

Thesecondconstructor–withoutparameters

Polynomial::Polynomial(){ coeff = 0 ; // There are no elements in the array size = 0;

}

YoumayalternativelyuseaninitializationlistPolynomial::Polynomial():coeff(0),size(0){

}

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Third Constructor

Copyconstructor:createsanobjectbasedonanexistingobject.Invokedwhenthiscommandsareexecuted:Polynomial p1copy(p1)

Polynomial p2copy = p2

Questions:

Why is it needed? What will the default copy constructor do for the Polynomial class?

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The Destructor

Polynomial::~Polynomial() { delete [] coeff ; // deallocate memory for array

}

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The add function

Polynomial Polynomial::add( const Polynomial& right) const {

int temp_size = max(this->size,right.size);

double *temp = new double[temp_size]; // allocate temp array

//Add array in parameter list to array in current object “this”

//Place the resulting polynomial in array temp

// create a new polynomial with the result of addition

Polynomial p(temp_size,temp) ;

delete [] temp; // delete temp array

return p;

}

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A “+ “ operator

Polynomial Polynomial::operator+(const Polynomial& right) {

int temp_size = max(this->size,right.size);

double *temp = new double[temp_size]; // allocate temp array

//Add array in parameter list to array in current object “this”

//Place the resulting polynomial in array temp

// create a new polynomial with the result of addition

Polynomial p(temp_size,temp) ;

delete [] temp; // delete temp array

return p;

}

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The this keyword

int temp_size = max( this->size ,right.size);

ü  this is a pointer to the current object

ü  *this is the value of the current object

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Using Polynomial “+” operator

int main() {

double p1_array[] = {0.0,1.0,1.0}; Polynomial p1(3,p1_array); // 3 -terms – 0 + X + X**2 double p2_array[] = {1.0,0.0,1.0,2.0}; Polynomial p2(4,p2_array); //4-terms 1 + 0*X + X**2 + 2X**3

Polynomial p3; p3 = p1 + p2;

}

“=“needstobedefined

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Polynomial “=” operator // assignment operator that is exception safe - uses the copy-swap idiom Polynomial& Polynomial::operator=(const Polynomial& other) // copy assignment {

// make a copy of the right hand side Polynomial temp(other);

//Now, swap the data members with the temporary

std::swap(size,temp.size); std::swap(coeff,temp.coeff);

return *this ; }

Contentofobject

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Exercise 2 – 10 min

• CompletethePolynomialclass

1.  Writeevaluate()function–evaluatespolynomialatagivenvalue2.  Testallfunctionsandoperators

ü Considerdifferenttestcasesfor“+”operatorü Testthecomparisonoperator(==)

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Exercise 3 (lab/home practice)

Completeothermemberfunctionsintheinitialclassdesign:1.  diff2.  mult3.  derivative

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Summary

•  ReviewObjectOrientedProgramingü Classes–Userdefinedtypesü ClassDesign–UMLnotation

•  ReviewC++ü C++arraysü Pointersü Dynamicmemoryallocationü Constructorsü Destructorü Parameterpassingü Overloadingoperators

•  DesignandimplementaC++classü Hands-onExample:APolynomialClass

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Resources

OnUML•  UMLDistilled:ABriefGuidetotheStandardObjectModelingLanguage(3rdEdition)byMartinFowler,Feb242004.

OnC++•  DataAbstraction&ProblemSolvingwithC++:WallsandMirrors(7thEdition)bybyFrankM.Carrano,TimothyM.Henry,Mar142016• https://www.tutorialspoint.com/cplusplus/• http://www.cplusplus.com• https://www.learncpp.com/

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References

•  https://en.wikipedia.org/wiki/Class_diagramClassdiagram•  http://www.cplusplus.com/articles/y8hv0pDG/Copyconstructors,assignmentoperators,andexceptionsafeassignment•  https://en.wikipedia.org/wiki/Assignment_operator_(C%2B%2B)

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