哪位大神帮忙编写一个将输入复制到输出的程序，并将其中的多个空格用一个空格代替

#include <iostream>
#include <string>

using namespace std;

void main()
{
    cout<<"Please enter a word:"<<endl;

    istreambuf_iterator<char> beg(cin),end;

    if(cin.fail())
    {
        cout<<"Error!"<<endl;
    }
    else
    {
        string str(beg,end);
        size_t len=0;

        for(string::iterator sbeg=str.begin();sbeg!=str.end();++sbeg)
        {
            if(*sbeg==' ')
            {
                for(string::iterator tmp=sbeg;*tmp==' ';++tmp,++len);
                str.erase(sbeg,len+sbeg);
                str.insert(sbeg,' ');
                len=0;
            }
        }
        cout<<"The result is:"<<endl<<str<<endl;
    }

    system("pause");
}