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<b>Data Structures and Algorithms 
with Object-Oriented Design Patterns in C++</b><br>
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<H3><A NAME="SECTION0018331000000000000000">Mutators</A></H3>
<P>
A <em>mutator</em><A NAME=57364>&#160;</A> is a member function that can modify an object.
Every non-<tt>const</tt> member function of a class is a mutator.
In the simplest case,
a mutator just assigns a new value to one of the member variables.
In general,
a mutator performs some computation
and modifies any number of member variables.
<P>
Program&nbsp;<A HREF="page604.html#progcomplex3c" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/page604.html#progcomplex3c"><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> defines three mutators for the <tt>Complex</tt> class.
The first two, <tt>SetReal</tt> and <tt>SetImag</tt>,
simply assign new values to the <tt>real</tt> and <tt>imag</tt> member variables,
respectively.
<P>
<P><A NAME="57747">&#160;</A><A NAME="progcomplex3c">&#160;</A> <IMG WIDTH=575 HEIGHT=238 ALIGN=BOTTOM ALT="program57372" SRC="img2604.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/img2604.gif"  ><BR>
<STRONG>Program:</STRONG> <tt>Complex</tt> Class Mutators<BR>
<P>
<P>
Program&nbsp;<A HREF="page604.html#progcomplex3c" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/page604.html#progcomplex3c"><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> also shows how
the assignment operator, <tt>operator=</tt>, can be
<em>overloaded</em><A NAME=57387>&#160;</A><A NAME=57388>&#160;</A>.
By overloading the assignment operator in this way
the function is called whenever
a complex number is assigned to another like this:
<PRE>c = d;</PRE>
<P>
If the programmer does not define an assignment operator explicitly,
the C++ compiler generates one.
The compiler-generated assignment operator simply assigns one-by-one
the member variables of the class
by invoking their respective assignment operators.
<P>
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