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137 lines
5.8 KiB
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<HTML>
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<HEAD>
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<TITLE>accumulate()</TITLE>
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<LINK REL=StyleSheet HREF="../rw.css" TYPE="text/css" TITLE="Apache stdcxx Stylesheet"></HEAD>
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<BODY BGCOLOR=#FFFFFF>
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<A HREF="II.html"><IMG SRC="images/bprev.gif" WIDTH=20 HEIGHT=21 ALT="Previous file" BORDER=O></A><A HREF="noframes.html"><IMG SRC="images/btop.gif" WIDTH=56 HEIGHT=21 ALT="Top of Document" BORDER=O></A><A HREF="booktoc.html"><IMG SRC="images/btoc.gif" WIDTH=56 HEIGHT=21 ALT="Contents" BORDER=O></A><A HREF="tindex.html"><IMG SRC="images/bindex.gif" WIDTH=56 HEIGHT=21 ALT="Index page" BORDER=O></A><A HREF="adjacent-difference.html"><IMG SRC="images/bnext.gif" WIDTH=25 HEIGHT=21 ALT="Next file" BORDER=O></A><DIV CLASS="DOCUMENTNAME"><B>Apache C++ Standard Library Reference Guide</B></DIV>
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<H2>accumulate()</H2>
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<P><B>Library:</B> <A HREF="2-10.html">Numerics</A></P>
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<PRE><HR><B><I>Function</I></B><HR></PRE>
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<UL>
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<LI><A HREF="#sec1">Local Index</A></LI>
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<LI><A HREF="#sec2">Summary</A></LI>
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<LI><A HREF="#sec3">Synopsis</A></LI>
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<LI><A HREF="#sec4">Description</A></LI>
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<LI><A HREF="#sec5">Complexity</A></LI>
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<LI><A HREF="#sec6">Example</A></LI>
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<LI><A HREF="#sec7">Standards Conformance</A></LI>
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</UL>
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<A NAME="sec1"><H3>Local Index</H3></A>
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No Entries
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<A NAME="sec2"><H3>Summary</H3></A>
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<P>A generalized numeric operation that accumulates all elements within a range into a single value</P>
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<A NAME="sec3"><H3>Synopsis</H3></A>
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<PRE>#include <numeric>
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namespace std {
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template <class InputIterator, class T>
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T accumulate(InputIterator start,
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InputIterator finish,
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T init);
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template <class InputIterator,
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class T,
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class BinaryOperation>
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T accumulate(InputIterator start,
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InputIterator finish,
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T init,
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BinaryOperation binary_op);
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}
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</PRE>
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<A NAME="sec4"><H3>Description</H3></A>
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<P><SAMP>accumulate()</SAMP> applies a binary operation to <SAMP>init</SAMP> and each value in the range <SAMP>[start,finish)</SAMP>. The result of each operation is returned in <SAMP>init</SAMP>. This process aggregates the result of performing the operation on every element of the sequence into a single value.</P>
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<P>The accumulator <SAMP>acc</SAMP> is initialized with the value <SAMP>init </SAMP>and modified with <SAMP>acc = acc + *i</SAMP> or <SAMP>acc = binary_op(acc, *i)</SAMP> for each interator <SAMP>i</SAMP>, in order, in the range <SAMP>[start, finish)</SAMP>.</P>
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<A NAME="sec5"><H3>Complexity</H3></A>
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<P><SAMP>accumulate()</SAMP> performs exactly <SAMP>finish-start</SAMP> applications of the binary operation, <SAMP>operator+ </SAMP>by default.</P>
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<A NAME="sec6"><H3>Example</H3></A>
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<UL><PRE>//
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// accum.cpp
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//
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#include <numeric> // for accumulate
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#include <vector> // for vector
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#include <functional> // for multiplies
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#include <iostream> // for cout
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int main ()
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{
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// Typedef for convenience.
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typedef std::vector<int, std::allocator<int> > vector;
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// Initialize a vector using an array of integers.
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const vector::value_type arr[] =
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{ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
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vector v1 (arr, arr + sizeof arr / sizeof *arr);
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// Accumulate sums and products.
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vector::value_type sum =
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std::accumulate (v1.begin (), v1.end (), 0);
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vector::value_type prod =
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std::accumulate (v1.begin (), v1.end (), 1,
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std::multiplies<vector::value_type>());
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// Output the results.
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std::cout << "For the series: ";
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for (vector::iterator i = v1.begin (); i != v1.end (); ++i)
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std::cout << *i << " ";
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std::cout << "where N = " << v1.size ()
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<< "\nThe sum = (N * N + N) / 2 = " << sum
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<< "\nThe product = N! = " << prod << std::endl;
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return 0;
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}
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Program Output:
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For the series: 1 2 3 4 5 6 7 8 9 10 where N = 10
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The sum = (N * N + N) / 2 = 55
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The product = N! = 3628800
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</PRE></UL>
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<UL><PRE></PRE></UL>
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<A NAME="sec7"><H3>Standards Conformance</H3></A>
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<P><I>ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 26.4.1</I></P>
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<BR>
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