inner_product (STL Sample)

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

Required Header:
<numeric>

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

template<class InputIterator1, class InputIterator2, class T, class BinOp1, class BinOp2> 
     inline T inner_product(InputIterator1 first, InputIterator1 last, InputIterator2 first2,
     T init, BinOp1 binary_op1, BinOp2 binary_op2)

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:
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.
///////////////////////////////////////////////////////////////////////

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

using namespace std;


typedef vector < 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,
                            multiplies<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