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<b>Data Structures and Algorithms 
with Object-Oriented Design Patterns in C++</b><br>
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<H2><A NAME="SECTION0018310000000000000000">Member Variables and Member Functions</A></H2>
<P>
A class groups a set of values and a set of operations.
The values and the operations of a class are called its <em>members</em>.
<em>Member variables</em> implement the values
and <em>member functions</em> implement the operations.
<P>
Suppose we wish to define a class to represent
<em>complex numbers</em><A NAME=57225>&#160;</A>.
The <tt>Complex</tt> class definition shown in Program&nbsp;<A HREF="page597.html#progcomplex1h" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/page597.html#progcomplex1h"><IMG  ALIGN=BOTTOM ALT="gif" SRC="cross_ref_motif.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/icons/cross_ref_motif.gif"></A>
illustrates how this can be done.
Two member variables, <tt>real</tt> and <tt>imag</tt>, are declared.
These represent the real and imaginary parts
of a complex numbers (respectively).
<P>
<P><A NAME="57726">&#160;</A><A NAME="progcomplex1h">&#160;</A> <IMG WIDTH=575 HEIGHT=410 ALIGN=BOTTOM ALT="program57230" SRC="img2601.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/img2601.gif"  ><BR>
<STRONG>Program:</STRONG> <tt>Complex</tt> Class Definition<BR>
<P>
<P>
Every object instance of the <tt>Complex</tt>
class contains its own member variables.
Consider the following variable declarations:
<PRE>Complex c;
Complex d;</PRE>
Both <tt>c</tt> and <tt>d</tt> are instances of the complex class.
Therefore, each of them has a <tt>real</tt> and <tt>imag</tt> member variable.
The member variables of an object are accessed using the <em>dot</em> operator.
E.g., <tt>c.real</tt> refers to the <tt>real</tt> member variable of <tt>c</tt>
and <tt>d.imag</tt> refers to the <tt>imag</tt> member of <tt>d</tt>.
<P>
The <tt>Complex</tt> class definition also contains
a list of function prototypes
which declare the <em>member functions</em> of the class.
In general,
a member function performs some operation on an instances of the class.
Again, the <em>dot</em> operator is used to specify the object on which
the operation is performed.
E.g., <tt>c.SetReal(1.0)</tt> invokes the <tt>SetReal</tt> function on <tt>c</tt>
and <tt>d.Put(cout)</tt> invokes the <tt>Put</tt> function on <tt>d</tt>.
<P>
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