C++ Tutorial/STL Algorithms Helper/accumulate

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.
*/

1. include <iostream>
2. include <vector>
3. include <deque>
4. include <list>
5. include <set>
6. include <map>
7. include <string>
8. include <algorithm>
9. include <iterator>
10. include <functional>
11. 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>

1 2 3 4 5 6 7 8 9
product: 362880
product: 0

Calculate sum of elements in a vector

<source lang="cpp">#include <iostream> using std::cout; using std::endl;

1. include <algorithm>
2. include <numeric>
3. include <vector>
4. 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>

Vector v2 contains: 100 2 8 1 50 3 8 8 9 10
The total of the elements in Vector v is: 199

Demonstrating the generic accumulate algorithm with a reverse iterator

<source lang="cpp">#include <iostream>

1. include <vector>
2. include <cassert>
3. 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>

Values to be added:
1
4.470348358e-008
2.980232239e-008
1.490116119e-008
1.490116119e-008
Sum accumulated from right = 1.000000119

Illustrating the generic accumulate algorithm with predicate

<source lang="cpp">#include <iostream>

1. include <cassert>
2. include <algorithm>
3. include <functional>
4. 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>

240

The total of the elements in a vector

<source lang="cpp">#include <iostream>

1. include <algorithm>
2. include <numeric>
3. 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>