STL Sample for the partial_sum Function

ID: Q157393

The information in this article applies to:

The Standard C++ Library included with: - Microsoft Visual C++, 32-bit Edition, version 4.2

SUMMARY

The sample code below illustrates how to use partial_sum STL function in Visual C++.

MORE INFORMATION

Required Header

   #include <numeric>
   #include <functional>

Prototype

   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 may 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)
// 
// Written by Shaun Miller
// of Microsoft Product Support Services, Languages Developer Support.
// Copyright (c) 1996 Microsoft Corporation. All rights reserved.
/////////////////////////////////////////////////////////////////////// 

#include <iostream>
#include <numeric>
#include <functional>
#include <vector>
#include <iterator>

typedef vector < int, allocator < 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(),times<int>());

    // Print the array of partial products
    cout << "Array of partial products: ";
    partial_sum(rgIresult.begin(),rgIresult.end(),itOstream);
    cout << endl;

}

The 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

REFERENCES

Visual C++ Books On Line: Visual C++ Books:C/C++:Standard C++ Library Reference.

Additional query words: STL STLSample partial_sum

Keywords          : kbcode STLIss 
Version           : WINNT:4.2;
Platform          : NT WINDOWS
Issue type        : kbhowto

Last Reviewed: October 10, 1997