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2010-05-25T14:21:17Z

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2010-05-25T10:29:57Z

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==Algorithm: Use accumulate to calculate product==

<source lang="cpp">//
/* The following code example is taken from the book
* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
#include <iostream>
#include <vector>
#include <deque>
#include <list>
#include <set>
#include <map>
#include <string>
#include <algorithm>
#include <iterator>
#include <functional>
#include <numeric>
using namespace std;
/* PRINT_ELEMENTS()
* - prints optional C-string optcstr followed by
* - all elements of the collection coll
* - separated by spaces
*/
template <class T>
inline void PRINT_ELEMENTS (const T& coll, const char* optcstr="")
{
typename T::const_iterator pos;
std::cout << optcstr;
for (pos=coll.begin(); pos!=coll.end(); ++pos) {
std::cout << *pos << " ";
}
std::cout << std::endl;
}
/* INSERT_ELEMENTS (collection, first, last)
* - fill values from first to last into the collection
* - NOTE: NO half-open range
*/
template <class T>
inline void INSERT_ELEMENTS (T& coll, int first, int last)
{
for (int i=first; i<=last; ++i) {
coll.insert(coll.end(),i);
}
}

int main()
{
vector<int> coll;
INSERT_ELEMENTS(coll,1,9);
PRINT_ELEMENTS(coll);

// process product of elements
cout << "product: "
<< accumulate (coll.begin(), coll.end(), // range
1, // initial value
multiplies<int>()) // operation
<< endl;
// process product of elements (use 0 as initial value)
cout << "product: "
<< accumulate (coll.begin(), coll.end(), // range
0, // initial value
multiplies<int>()) // operation
<< endl;
}</source>
<pre class=codeResult>1 2 3 4 5 6 7 8 9
product: 362880
product: 0</pre>

==Calculate sum of elements in a vector==

<source lang="cpp">#include <iostream>
using std::cout;
using std::endl;
#include <algorithm>
#include <numeric>
#include <vector>
#include <iterator>
int main()
{
std::ostream_iterator< int > output( cout, " " );
int a2[ 10 ] = { 100, 2, 8, 1, 50, 3, 8, 8, 9, 10 };
std::vector< int > v2( a2, a2 + 10 ); // copy of a2
cout << "\n\nVector v2 contains: ";
std::copy( v2.begin(), v2.end(), output );
// calculate sum of elements in v
cout << "\n\nThe total of the elements in Vector v is: "
<< std::accumulate( v2.begin(), v2.end(), 0 );
cout << endl;
return 0;
}</source>
<pre class=codeResult>Vector v2 contains: 100 2 8 1 50 3 8 8 9 10
The total of the elements in Vector v is: 199</pre>

==Demonstrating the generic accumulate algorithm with a reverse iterator==

<source lang="cpp">#include <iostream>
#include <vector>
#include <cassert>
#include <numeric> // For accumulate
using namespace std;
int main()
{
float small = (float)1.0/(1 << 26);
float x[5] = {1.0, 3*small, 2*small, small, small};

vector<float> vector1(&x[0], &x[5]);
cout << "Values to be added: " << endl;
vector<float>::iterator i;
cout.precision(10);
for (i = vector1.begin(); i != vector1.end(); ++i)
cout << *i << endl;
cout << endl;
float sum1 = accumulate(vector1.rbegin(), vector1.rend(),(float)0.0);
cout << "Sum accumulated from right = " << (double)sum1 << endl;
return 0;
}</source>
<pre class=codeResult>Values to be added:
1
4.470348358e-008
2.980232239e-008
1.490116119e-008
1.490116119e-008
Sum accumulated from right = 1.000000119</pre>

==Illustrating the generic accumulate algorithm with predicate==

<source lang="cpp">#include <iostream>
#include <cassert>
#include <algorithm>
#include <functional>
#include <numeric>
using namespace std;
int main()
{
int x[20];

for (int i = 0; i < 20; ++i)
x[i] = i;
// Show that 10 * 1 * 2 * 3 * 4 == 240:
int result = accumulate(&x[1], &x[5], 10, multiplies<int>());
cout << result;

return 0;
}</source>
<pre class=codeResult>240</pre>

==The total of the elements in a vector==

<source lang="cpp">#include <iostream>
#include <algorithm>
#include <numeric>
#include <vector>
using namespace std;
int main()
{
const int SIZE = 10;
int a1[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
vector< int > v( a1, a1 + SIZE );
cout << "\n\nThe total of the elements in Vector v is: " << accumulate( v.begin(), v.end(), 0 );
return 0;
}</source>

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