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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="SECTION008113000000000000000">Finding Items in a List</A></H3>
<P>
Program&nbsp;<A HREF="page171.html#proglist2c" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/page171.html#proglist2c"><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 two <tt>ListAsArray</tt> class
accessor functions which search for an object in the ordered list.
The <tt>IsMember</tt> function tests whether a particular object
instance is in the ordered list.
The <tt>Find</tt> function locates in the list
an object which <em>matches</em> its argument.
<P>
<P><A NAME="9606">&#160;</A><A NAME="proglist2c">&#160;</A> <IMG WIDTH=575 HEIGHT=295 ALIGN=BOTTOM ALT="program9447" SRC="img788.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/img788.gif"  ><BR>
<STRONG>Program:</STRONG> <tt>ListAsArray</tt> Class <tt>IsMember</tt> and 	<tt>Find</tt> Member Function Definitions<BR>
<P>
<P>
The <tt>IsMember</tt> function is a Boolean-valued function
which takes as its lone argument a <tt>const</tt> reference to an <tt>Object</tt>.
This function compares one-by-one the pointers contained in <tt>array</tt>
with the <em>address</em> of the argument.
Thus, this function tests whether <em>a particular object instance</em>
is contained in the ordered list.
In the worst case, the object sought is not in the list.
In this case, the running time of the function is <I>O</I>(<I>n</I>),
where  <IMG WIDTH=72 HEIGHT=9 ALIGN=BOTTOM ALT="tex2html_wrap_inline61308" SRC="img709.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/img709.gif"  > is the number of items in the ordered list.
<P>
The <tt>Find</tt> function also does a search of the ordered list.
It also takes a single argument which is a <tt>const</tt> reference to
an <tt>Object</tt>.
However, find does not compare addresses.
Instead, it uses <tt>operator==</tt> to compare the items.
Thus, the <tt>Find</tt> function searches the list
for an object which compares equal to its argument.
The <tt>Find</tt> function returns a reference to the object found.
If no match is found,
it returns a reference to the <tt>NullObject</tt> instance.
The running time of this function depends on the time required
for the comparison operator,  <IMG WIDTH=89 HEIGHT=26 ALIGN=MIDDLE ALT="tex2html_wrap_inline61648" SRC="img789.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/img789.gif"  >.
In the worst case, the object sought is not in the list.
In this case the running time is  <IMG WIDTH=172 HEIGHT=26 ALIGN=MIDDLE ALT="tex2html_wrap_inline61650" SRC="img790.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/img790.gif"  >.
For simplicity, we will assume that the comparison
takes a constant amount of time.
Hence, the running time of the function is also <I>O</I>(<I>n</I>),
where  <IMG WIDTH=72 HEIGHT=9 ALIGN=BOTTOM ALT="tex2html_wrap_inline61308" SRC="img709.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/img709.gif"  > is the number of items in the list.
<P>
It is important to understand the
subtle distinction between the search done by the
<tt>IsMember</tt> function and and that done by <tt>Find</tt>.
The <tt>IsMember</tt> function searches for a specific object instance
while <tt>Find</tt> simply looks for a matching object.
Consider the following:
<PRE>Object&amp; object1 = *new Int (57);
Object&amp; object2 = *new Int (57);
ListAsArray list (1);
list.Insert (object1);</PRE>
This code fragment creates two <tt>Int</tt> class object instances,
both of which have the value&nbsp;57.
Only the first object, <tt>object1</tt>,
is inserted into the ordered list <tt>list</tt>.
Consequently, the function call
<PRE>list.IsMember (object1)</PRE>
returns <tt>true</tt>;
whereas the function call
<PRE>list.IsMember (object2)</PRE>
returns <tt>false</tt>.
<P>
On the other hand,
if a search is done using the <tt>Find</tt> function like this:
<PRE>Object&amp; object3 = list.Find (object2);</PRE>
the search will be successful!
After the call, <tt>object3</tt> refers to <tt>object1</tt>.
<P>
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