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2.2 Members

After the long plea for classes, it is high time to define one. A class defines a new data type which can contain

Data: referred to as Member Variables; the standard also calls it Data Members; another term for it is Fields;

Functions: referred to as Methods or Member Functions;

Type definitions; and

Contained classes.

Data members and methods are discussed in this section.

2.2.1 Member Variables A concise class example is a type for representing complex numbers. Of course, there already exists such a class in C++ but for illustration purposes we write our own:

class complex {

 public:
   double r, i;

}; The class contains variables to store the real and the imaginary parts of a complex number. A common mental picture for the role of a class definition is a blueprint. That is, we have not yet defined any single complex number. We only said that complex numbers contain two variables of type double which are named r and i. Now we are going to create Objects of our type:

Click here to view code image

complex z, c; z.r= 3.5; z.i= 2; c.r= 2; c.i= - 3.5; std::cout ≪ “z is (” ≪ z.r ≪ “, ” ≪ z.i ≪ “)\n”; This snippet defines the objects z and c with variable declarations. Such declarations do not differ from intrinsic types: a type name followed by a variable name or a list thereof. The members of an object can be accessed with the dot operator . as illustrated above. As we can see, member variables can be read and written like ordinary variables—when they are accessible.