68 3 Numerical differentiation and interpolation
intmain ()
{
Complex a(0.1,1.3);// we declare a complex variable a
Complex b(3.0), c(5.0,-2.3);// we declare complex variables b and c
Complex d = b; // we declare a new complex variable d
cout <<"d="<< d <<", a="<< a <<", b="<< b << endl;
d = a*c + b/a;// we add, multiply and divide two complex numbers
cout <<"Re(d)="<< d.Re() <<", Im(d)="<< d.Im() << endl;// write out of the real
and imaginary parts
}
We include the header file complex.h and define four differentcomplex variables. These
area= 0. 1 +ı 1. 3 ,b= 3. 0 +ı 0 (note that if you don’t define a value for the imaginary part
this is set to zero),c= 5. 0 −ı 2. 3 andd=b. Thereafter we have defined standard algebraic
operations and the member functions of the class which allows us to print out the real and
imaginary part of a given variable.
To achieve these features, let us see how we define the complexclass. In C++ we could
define a complex class as follows
classComplex
{
private:
doublere, im;// real and imaginary part
public:
Complex (); // Complex c;
Complex (doublere,doubleim = 0.0);// Definition of a complex variable;
Complex (constComplex& c); // Usage: Complex c(a); // equate two complex variables
Complex&operator= (constComplex& c);// c = a; // equate two complex variables, same
as previous
~Complex (){} // destructor
doubleRe ()const; // double real_part = a.Re();
doubleIm ()const; // double imag_part = a.Im();
doubleabs () const; // double m = a.abs(); // modulus
friendComplexoperator+ (constComplex& a,constComplex& b);
friendComplexoperator- (constComplex& a,constComplex& b);
friendComplexoperator*(constComplex& a,constComplex& b);
friendComplexoperator/ (constComplex& a,constComplex& b);
};
The class is defined via the statementclass Complex. We must first use the key word
class, which in turn is followed by the user-defined variable nameComplex. The body of the
class, data and functions, is encapsulated within the parentheses{...};.
Data and specific functions can be private, which means that they cannot be accessed from
outside the class. This means also that access cannot be inherited by other functions outside
the class. If we useprotectedinstead ofprivate, then data and functions can be inherited
outside the class. The key wordpublicmeans that data and functions can be accessed from
outside the class. Here we have defined several functions which can be accessed by functions
outside the class. The declarationfriendmeans that stand-alone functions can work on pri-
vately declared variables of the type(re, im). Data members of a class should be declared
as private variables.
The first public function we encounter is a so-called constructor, which tells how we de-
clare a variable of typeComplexand how this variable is initialized. We have chosen three
possibilities in the example above:
- A declaration likeComplex c;calls the member functionComplex()which can have the
following implementation
Complex:: Complex (){re = im = 0.0;}
