How to use the accumulate, copy, and vector::push_back STL functions in Visual C++ (156807)

MORE INFORMATION

Required Header

   <numeric>
   <functional>
				

Prototype

   template<class InputIterator, class _TYPE> inline


      _TYPE accumulate(InputIterator first, InputIterator last, _TYPE init)

   template<class InputIterator, class _TYPE, class BinaryOperator> inline

      _TYPE accumulate(InputIterator first, InputIterator last, _TYPE init,
                       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

The accumulate function initializes an accumulator acc with an initial value init and then modifies it with acc = acc + *i or acc = binary_op(acc,*i) for every iterator i in the range [first, last) in order.

Normally, the accumulate function is used to sum the numeric elements of a vector. However, it can also be used to do other useful work such as concatenate a vector of strings.

Sample Code

   /////////////////////////////////////////////////////////////////////// 
   // 
   // Compile options needed: /GX
   // 
   // accumulate.cpp : Demonstrates the use of accumulate()
   // 
   // Description of accumulate(first,last,init)
   //                accumulate(first,last,init,binary_op):
   // 
   //    Initializes the accumulator acc with the initial value init
   //        acc = init
   //    and then modifies it with
   //        acc  =  acc + *i
   //    or
   //        acc = binary_op(acc, *i)
   //    for every iterator i in the range [first, last) in order.
   // 
   // Written by Shaun Miller
   // of Microsoft Product Support Services, Languages Developer Support.
   // Copyright (c) 1996 Microsoft Corporation. All rights reserved.
   /////////////////////////////////////////////////////////////////////// 

   // turn off warning about symbols too long for debugger
   #pragma warning (disable : 4786)

   #include <iostream>
   #include <numeric>
   #include <functional>
   #include <vector>
   #include <iterator>
   #include <string>
   
#if _MSC_VER > 1020   // if VC++ version is > 4.2
   using namespace std;  // std c++ libs implemented in std
   #endif

   typedef vector < float, allocator < float > > FloatArray;
   typedef vector < string, allocator < string > > StringArray;
   typedef ostream_iterator <float, char, char_traits <char> >
   FloatOstreamIt;

   void main ()
   {
       // a vector of floats
       FloatArray rgFA;

       // an ostream iterator that outputs a float to cout terminated
       // by a space
       FloatOstreamIt OstreamIt(cout," ");

       // Initialize the array to 1,1/2,1/3,...
       for (int i=0; i<10; i++) rgFA.push_back(1.0f/(i+1));

       // Print the array
       copy(rgFA.begin(),rgFA.end(),OstreamIt);
       cout << endl;

       // Sum the array
       cout << "The sum of 1 + 1/2 + 1/3 + ... + 1/10 is "
            << accumulate(rgFA.begin(),rgFA.end(),0.0f)
            << endl;

       // Compute the product of the array
       cout << "The product of 1 * 1/2 * 1/3 * ... * 1/10 is "
            << accumulate(rgFA.begin(),rgFA.end(),1.0f,multiplies<float>())
            << endl;

       // Initialize array of strings
       StringArray rgs;
       rgs.push_back("This ");
       rgs.push_back("is ");
       rgs.push_back("one ");
       rgs.push_back("sentence. ");

       // Concatenate the strings in the array & print the sentence
       cout << "The concatenated vector of strings: "
            << accumulate(rgs.begin(),rgs.end(),string(""))
            << endl;
   }
				

Program Output is:

1 0.5 0.333333 0.25 0.2 0.166667 0.142857 0.125 0.111111 0.1
The sum of 1 + 1/2 + 1/3 + ... + 1/10 is 2.92897
The product of 1 * 1/2 * 1/3 * ... * 1/10 is 2.75573e-007
The concatenated vector of strings: This is one sentence.