The sample code below illustrates how to use the partial_sum
STL function in Visual C++.
Required Header:
<numeric>
template<class InputIterator, class OutputIterator> inline
OutputIterator partial_sum(InputIterator first, InputIterator last, OutputIterator first2)
template<class InputIterator, class OutputIterator, class BinaryOperator> inline
OutputIterator partial_sum(InputIterator first, InputIterator last, OutputIterator first2,
BinaryOperator binary_op)
Note: The class/parameter names in the prototype do not match the version in the header file. Some have been modified to improve readability.
Description:
Assigns to every iterator i in the range [result,result + (last - first)) a value correspondingly equal to ((...(*first + *(first + 1)) + ...) + *(first + (i - result))) - or - binary_op(binary_op(..., binary_op(*first, *(first + 1)),...), *(first + (i - result))). In other words, *(result+i) = init + *(first+0) + *(first+1) + ... + *(first+i).
Sample Code:
///////////////////////////////////////////////////////////////////////
//
// Compile options needed: /GX
//
// partial_sum.cpp : Demonstrates the use of partial_sum().
//
// Description of partial_sum(first,last,first2,init)
// partial_sum(first,last,first2,init,binary_op):
//
// Assigns to every iterator i in the range
// [result,result + (last - first)) a value correspondingly equal to
// ((...(*first + *(first + 1)) + ...) + *(first + (i - result)))
//
// - or -
//
// binary_op(binary_op(..., binary_op(*first, *(first + 1)),...),
// *(first + (i - result)))
//
// In other words,
// *(result+i) = init + *(first+0) + *(first+1) + ... + *(first+i)
///////////////////////////////////////////////////////////////////////
#include <iostream>
#include <numeric>
#include <functional>
#include <vector>
#include <iterator>
using namespace std;
typedef vector < int > IntArray;
typedef ostream_iterator < int, char, char_traits<char> > IntOstreamIt;
void main ()
{
IntOstreamIt itOstream(cout," ");
// Initialize the array
IntArray rgI;
for (int i=1; i<=10; i++) rgI.push_back(i);
// Print the arrays
cout << "Array: ";
copy(rgI.begin(),rgI.end(),itOstream);
cout << endl;
// The result array must be at least the same size as the data array
IntArray rgIresult(rgI.size());
// Compute the partial sum of the array
partial_sum(rgI.begin(),rgI.end(),rgIresult.begin());
// Print the array of partial sums
cout << "Array of partial sums: ";
copy(rgIresult.begin(),rgIresult.end(),itOstream);
cout << endl;
// Compute the partial product of the array
partial_sum(rgI.begin(),rgI.end(),rgIresult.begin(),multiplies<int>());
// Print the array of partial products
cout << "Array of partial products: ";
partial_sum(rgIresult.begin(),rgIresult.end(),itOstream);
cout << endl;
}
Program Output is:
Array: 1 2 3 4 5 6 7 8 9 10
Array of partial sums: 1 3 6 10 15 21 28 36 45 55
Array of partial products: 1 3 9 33 153 873 5913 46233 409113 4037913