STL Sample for the inner_product Function

ID: Q157392

The information in this article applies to:

SUMMARY

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

MORE INFORMATION

Required Header

   #include <numeric>
   #include <functional>

Prototype

   template<class InputIterator1, class InputIterator2, class _TYPE>
       inline _TYPE inner_product(InputIterator first, InputIterator last,
                           InputIterator first2, _TYPE init)

   template<class InputIterator1, class InputIterator2, class _TYPE,
            class BinaryOperator1, class BinaryOperator2> inline
       _TYPE inner_product(InputIterator1 first, InputIterator1 last,
                           InputIterator2 first2, _TYPE init,
                           BinaryOperator1 binary_op1,
                           BinaryOperator2 binary_op2)
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

inner_product computes its result by initializing the accumulator acc with init and then modifying it with: 

    acc = acc  +  (*i1) * (*i2)

    - or -

    acc = binary_op1(acc, binary_op2(*i1, *i2))
for every iterator i1 in the range [first, last) and iterator i2 in the range [first2, first2 + (last - first)) in order.

Sample Code

/////////////////////////////////////////////////////////////////////// 
// 
// Compile options needed: /GX
// 
// inner_product.cpp : Demonstrates the use of inner_product().
// 
// Description of
//         inner_product(first,last,first2,init)
//         inner_product(first,last,first2,init,binary_op1,binary_op2):
// 
//    Computes its result by initializing the accumulator acc with init
//        acc = init
//    and then modifying it with
//        acc = acc  +  (*i1) * (*i2)
//    or
//        acc = binary_op1(acc, binary_op2(*i1, *i2))
//    for every iterator i1 in the range [first, last) and
//    iterator  i2  in  the  range [first2, first2 + (last - first))
//    in order.
// 
// 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 < float, allocator < float > > FloatArray; typedef ostream_iterator < float, char, char_traits<char> > FloatOstreamIt; 

void main ()
{ 
    FloatOstreamIt itOstream(cout," ");

    // Initialize the arrays
    FloatArray rgF1, rgF2;
    for (int i=1; i<=5; i++) {
        rgF1.push_back(i);
        rgF2.push_back(i*i);
    };

    // Print the arrays
    cout << "Array 1: ";
    copy(rgF1.begin(),rgF1.end(),itOstream);
    cout << endl;
    cout << "Array 2: ";
    copy(rgF2.begin(),rgF2.end(),itOstream);
    cout << endl;

    // Compute the inner_product of the arrays
    // This is the sum of the products (S.O.P) of the corresponding
elements 
    float ip1 = inner_product(rgF1.begin(),rgF1.end(),rgF2.begin(),0);
    cout << "The inner product (S.O.P) of Array1 and Array2 is "
       << ip1
       << endl;

    // Compute the inner_product of the arrays
    // This is the product of the sums (P.O.S.) of the corresponding
elements 
    float ip2 = inner_product(rgF1.begin(),rgF1.end(),rgF2.begin(),1,
                            times<float>(),plus<float>());
    cout << "The inner product (P.O.S.) of Array1 and Array2 is "
       << ip2
       << endl;
}

Program Output is:

Array 1: 1 2 3 4 5 Array 2: 1 4 9 16 25 The inner product (S.O.P) of Array1 and Array2 is 225 The inner product (P.O.S.) of Array1 and Array2 is 86400

REFERENCES

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

Additional query words: STL STLSample inner_product 

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

Last Reviewed: October 10, 1997