为什么在尝试输出字符串时出现此错误？

Question

I get the error when using cout in main function at end

   #include "string"
#include "stdafx.h"
#include"iostream"

using namespace std;

string first[] = { "","one","two","three","four","five","six","seven","eight","nine","ten","eleven",
"twelve","thirteen","fourteen","fifteen","sixteen","seventeen","eighteen","nineteen" };

string second[] = { "","","twenty","thirty","fourty","fifty","sixty","seventy","eighty","ninety" };

string lessThan100(int b)
{

    if (b < 20) { return first[b]; }//accounts for numbers that don't follow pattern ie 11 to 19

    return second[b / 10] + first[b % 10]; // dividing by 10 front number modding by 10 gives back number
}

string intToString(int a)
{
    string output = "";
    for (int x = log10(a); x >= 0; x = x - 3)
    {
        if (x >= 9)
        {
            int num = a / 1000000000;//dividing by a billion gives the # of billions
            if (num<99) { return "error number too large"; }

            output = output + lessThan100(num) + " billion ";

        }
        else if (x >= 6)
        {
            int num = a % 1000000000 / 1000000; //modding by a billion leaves the millions dividing by million gives # of millions
            output = output + lessThan100(num) + " million ";

        }
        else if (x >= 3)
        {
            string over100 = "";
            int num = a % 1000000 / 1000;//modding by a million leaves the thousands dividing by a thousand gives # of thousands
            if (num >= 100) { over100 = first[num / 100] + " hundred "; }//we can have more than 99 thousand so we account for that
            output = output + over100 + lessThan100(num) + " thousand ";

        }
        else if (x >= 0)
        {
            string over100 = "";
            int num = a % 1000;//moding by 1000 gives hundreds
            if (num >= 100) { over100 = first[num / 100] + " hundred "; }//accounts for number higher than 99
            output = output + over100 + lessThan100(num);
        }
    }
}

int main()
{
    int number = 19;
    string word = intToString(19);
    cout << word;
    return 0;
}

I get this error binary '<<': no operator found which takes a right-hand operand of type 'std::string' (or there is no acceptable conversion). The program runs fine when I remove cout << word; I really just want to see if intToString() is working.

Answer 1

The headers you need are:

#include <string>
#include <iostream>

and they must come after the include of stdafx.h . The MS compiler ignores any lines that are before stdafx.h . The reasons why can be found in this answer (to a related question) but they basically boil down to the way MSVC does precompiled headres.

Answer 2

well, you should know that when you use " ", it tells the compiler to search for the head-file in local directory, while if you use <>, it tells the compiler to find head file in system directory. so, I suggest you to try use <> to #inlcude