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Engineering Problem Solving With C++ An Object Based Approach Additional Topics Chapter 10 Programming with Classes

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Overloading Operators Allows a programmer defined data type to be used in the same way that a predefined data type is used. Definitions for operator functions are included in a class definition in the same way as member functions –keyword operator is used followed by the name of the function. –the name of the function is one of the predefined C++ operators Only predefined operators may be overloaded All predefined operators except(. ::.* ?: sizeof) may be overloaded.

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Complex Number Class 4A complex number is a number that has two components; the real component and the imaginary component. a + bi 4Arithmetic is defined as follows: (a + bi) + (c + di) = (a + c) + (b + d)i (a + bi) - (c + di) = (a - c) + (b - d)i (a + bi) * (c + di) = (ac - bd) + (ad + bc)i (a + bi) / (c + di) = (ac + bd) / (c**2+d**2) + [ (bc -ad) /(c**2+d**2)]i

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Class Declaration class complex { public: complex(); complex(double,double); void print(ostream&); void input(istream&); complex operator+(complex&) const; complex operator-(complex&) const; complex operator*(complex&) const; complex operator/(complex&) const; private: double real, imag; };

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Implementation - constructors complex::complex() : real(0), imag(0) { //default constructor } complex :: complex(double r, double im) : real(r), imag(im) {//parameterized constructor }

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Implementation – Overloaded Operators complex complex::operator+(complex& c) const { complex temp; temp.real = real + c.real; temp.imag = imag + c.imag; return temp; }

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Implementation - Continued complex complex::operator/(complex& c) const { complex temp; temp.real = (real*c.real + imag*c.imag)/ ( pow(c.real,2) + pow(imag,2) ); temp.imag = (imag*c.real - real*c.imag)/ ( pow(c.real,2) + pow(imag,2) ); return temp; }

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Practice! – Implement the * operator (a + bi) * (c + di) = (ac - bd) + (ad + bc)i complex complex::operator*(complex& c) const { complex temp; temp.real = real*c.real – imag*c.imag; temp.imag = real*c.imag + imag*c.real; return temp; }

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Test Program complex c1, c2, c3;//declare three complex variables c1.input(cin); c2.input(cin); //test addition c3 = c1 + c2;// using overloaded operator + cout << endl << "c1 + c2 is "; c3.print(cout); //test division c3 = c1 / c2; // using overloaded operator / cout << endl << "c1 / c2 is "; c3.print(cout); cout << endl;

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Sample Output 4Using the following input: 4.4 1.5 3.5 -2.5 4The expected output from our test program will be: c1 + c2 is 7.9 + -1i c1 / c2 is 0.62973 + 0.878378i

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Variations Overloading Operators as: –member functions –friend functions –top level (non-member) functions

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Member Functions binary operators (ie +,-, * ) –member function requires one argument –the left hand operand is the object invoking the operator unary operator –member function requires no arguments –assumed to be prefix version of operators ++ and – –postfix versions of operators ++ and – are not covered in this text Disadvantages –first argument must be an object of the class

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Example – class complex In complex.h –complex operator +(complex c); operator + implemented in complex.cpp In a client program complex a, b, c; c = a + b; //a is calling object, b is argument c = a + 54.3; //OK, constructor is called to // convert 54.3 to complex object c = 54.3 + a // is not allowed

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Friend Functions binary operators –friend function requires two arguments unary operator –friend function requires one argument Disadvantage –A friend function is NOT a member function –Friend functions violate a strict interpretation of object oriented principals (implementation is hidden) –Recommended for operator overloading only

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Example: In class definition: friend complex operator +(complex c1, complex c2); In class implementation: complex operator +(complex c1, complex c2) { complex temp; temp.real = c1.real + c2.real; temp.imag = c1.imag + c2.imag; return temp; } In client program: complex cA, cB, cC; cC = cA+cB; cC = 54.3 + cB; //this is ok, when + is a friend function

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Class Declaration class complex { public: complex(); complex(double,double); friend ostream& operator <<(ostream&, complex); friend istream& operator >>(istream&, complex&); complex operator+(complex&) const; complex operator-(complex&) const; complex operator*(complex&) const; complex operator/(complex&) const; private: double real, imag; };

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Implementation ostream& operator <<(ostream& os, complex r) {os << r.real << + << r.imag << i; return os; } istream& operator >> (istream& is, complex& r) {is >> r.real >> r.imag; return is; }

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Error Checking on input operator 4If your input fails because of incorrect format, your function should mark the state of the istream as bad is.clear(ios::badbit | is.rdstate() ) 4clear resets entire error state to zero 4clear(ios::badbit) clears all and sets badbit 4is.rdstate() returns the previous state of all bits 4Statement sets the bit vector to the bitwise OR of badbit with previous state 4Failure can be tested with is.fail()

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Top Level (Non-Member) Functions binary operators –top level function requires two arguments unary operator –top level function requires one argument Disadvantage: –Top level functions do not have access to private data members. Function must use accessor functions.

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Example of top level function Function prototype in client program. complex operator +(complex c1, complex c2); Implemention in client program. complex operator +(complex c1, complex c2) { return complex(c1.get_real() + c2.get_real(), c1.get_imag() + c2.get_imag()); } Use in client program. complex cA, cB, cC; cC = cA + cB; cC = 54.3 + cA;//this is ok, when + is a top level //function

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