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<H2>count, count_if</H2>
<HR><PRE>     Algorithm</PRE><HR>
<A NAME="Summary"><H3>Summary</H3></A>
<P>Count the number of elements in a container that satisfy a given condition.</P>
<H3>Contents</H3>
<UL>
<A HREF="#Synopsis"><LI>Synopsis</LI></A>
<A HREF="#Description"><LI>Description</LI></A>
<A HREF="#Complexity"><LI>Complexity</LI></A>
<A HREF="#Example"><LI>Example</LI></A>
<A HREF="#Warnings"><LI>Warnings</LI></A>
</UL>
<A NAME="Synopsis"><H3>Synopsis</H3></A>
<PRE>#include &#60;algorithm></PRE>
<PRE>
template &#60;class InputIterator, class T, class Size>
 void count(InputIterator first, InputIterator last,
            const T&#38; value, Size&#38; n);
template &#60;class InputIterator, class Predicate, class Size>
 void count_if(InputIterator first, InputIterator last,
               Predicate pred, Size&#38; n);</PRE>
<A NAME="Description"><H3>Description</H3></A>
<P>The <B><I>count</B></I> algorithm compares <SAMP>value</SAMP> to elements in the sequence defined by iterators <SAMP>first</SAMP> and <SAMP>last</SAMP>, and increments a counting value <SAMP>n</SAMP> each time it finds a match.  i.e., <B><I>count</B></I> adds to <SAMP>n</SAMP> the number of iterators <SAMP>i</SAMP> in the range <SAMP>[first, last)</SAMP> for which the following condition holds:</P>
<PRE>*i == value</PRE>
<P>The <B><I>count_if</B></I> algorithm lets you specify a predicate, and increments <SAMP>n</SAMP> each time an element in the sequence satisfies the predicate.  That is, <B><I>count_if</B></I> adds to <SAMP>n</SAMP> the number of iterators <SAMP>i</SAMP> in the range <SAMP>[first, last)</SAMP> for which the following condition holds: </P>
<PRE>pred(*i) == true.</PRE>
<A NAME="Complexity"><H3>Complexity</H3></A>
<P>Both <B><I>count</B></I> and <B><I>count_if</B></I> perform exactly <SAMP>last-first</SAMP>  applications of the corresponding predicate.</P>
<A NAME="Example"><H3>Example</H3></A>
<PRE>//
// count.cpp
// 
 #include &#60;vector>
 #include &#60;algorithm>
 #include &#60;iostream.h>
 int main()
 {
   int sequence[10] = {1,2,3,4,5,5,7,8,9,10};
   int i=0,j=0,k=0;
   //
   // Set up a vector
   //
   vector&#60;int> v(sequence,sequence + 10);
   count(v.begin(),v.end(),5,i);  // Count fives 
   count(v.begin(),v.end(),6,j);  // Count sixes 
   //
   // Count all less than 8 
   // I=2, j=0
   //
   count_if(v.begin(),v.end(),bind2nd(less&#60;int>(),8),k);
   // k = 7
   cout &#60;&#60; i &#60;&#60; " " &#60;&#60; j &#60;&#60; " " &#60;&#60; k &#60;&#60; endl;
   return 0;
 }
Output :  2 0 7
</PRE>
<A NAME="Warnings"><H3>Warnings</H3></A>
<P>If your compiler does not support default template parameters then you need to always supply the <SAMP>Allocator</SAMP> template argument. For instance, you'll have to write:</P>
<PRE>vector &#60;int, allocator></PRE>
<PRE></PRE><P>instead of:</P>
<PRE>vector &#60;int></PRE>
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