C++ STD accumulate函數，stdaccumulate函數

C++ STD accumulate函數，stdaccumulate函數

1. 介紹

　　用來計算特定范圍內（包括連續的部分和初始值）所有元素的和，除此之外，還可以用指定的二進制操作來計算特定范圍內的元素結果。其頭文件在numeric中。

　　用次函數可以求和，構造前n項和的向量，乘積，構造前n項乘積的向量

2. 應用舉例

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

using namespace std;

int main( ) 
{

   vector <int> v1, v2( 20 );
   vector <int>::iterator Iter1, Iter2;

   int i;
   for ( i = 1 ; i < 21 ; i++ )
   {
      v1.push_back( i );
   }

   cout << "最初向量v1中個元素的值為:\n ( " ;
   for ( Iter1 = v1.begin( ) ; Iter1 != v1.end( ) ; Iter1++ )
      cout << *Iter1 << " ";
   cout << ")." << endl;

   // accumulate函數的第一個功能，求和
   int total;
   total = accumulate ( v1.begin ( ) , v1.end ( ) , 0 );

   cout << "整數從1到20的和為: " 
        << total << "." << endl;

   // 構造一個前n項和的向量
   int j = 0, partotal;
   for ( Iter1 = v1.begin( ) + 1; Iter1 != v1.end( ) + 1 ; Iter1++ )
   {
      partotal = accumulate ( v1.begin ( ) , Iter1 , 0 );
      v2 [ j ] = partotal;
      j++;
   }

   cout << "前n項和分別為:\n ( " ;
   for ( Iter2 = v2.begin( ) ; Iter2 != v2.end( ) ; Iter2++ )
      cout << *Iter2 << " ";
   cout << ")." << endl << endl;

   // accumulate函數的第二個功能，計算連乘積
   vector <int> v3, v4( 10 );
   vector <int>::iterator Iter3, Iter4;

   int s;
   for ( s = 1 ; s < 11 ; s++ )
   {
      v3.push_back( s );
   }

   cout << "向量v3的初始值分別為:\n ( " ;
   for ( Iter3 = v3.begin( ) ; Iter3 != v3.end( ) ; Iter3++ )
      cout << *Iter3 << " ";
   cout << ")." << endl;

   int ptotal;
   ptotal = accumulate ( v3.begin ( ) , v3.end ( ) , 1 , multiplies<int>( ) );

   cout << "整數1到10的連乘積為: " 
        << ptotal << "." << endl;

   // 構造一個前n項積的向量
   int k = 0, ppartotal;
   for ( Iter3 = v3.begin( ) + 1; Iter3 != v3.end( ) + 1 ; Iter3++ ) {
      ppartotal = accumulate ( v3.begin ( ) , Iter3 , 1 , multiplies<int>( ) );
      v4 [ k ] = ppartotal;
      k++;
   }

   cout << "前n項積分別為:\n ( " ;
   for ( Iter4 = v4.begin( ) ; Iter4 != v4.end( ) ; Iter4++ )
      cout << *Iter4 << " ";
   cout << ")." << endl;
}

編譯運行，看一下輸出結果：