String inserting text

#include <iostream>
#include <string>
#include <cstdlib>

using namespace std;
string ns;

 int main()
{

   string words = "one two three four five six";
   string word = "zero";
   int found = -1;
   int lastSpace = 0;
   do
   {
       found = words.find(" ", found+1);
       if(found!=-1)
       {
           lastSpace = found;
       }
   }
  // while(found<=words.length()-15);
      while(found!=-1);

   //words = words.substr(0,found) + " "+ word +words.substr(found);
   words = words.substr(0,lastSpace) + " "+ word +words.substr(lastSpace);


   cout << words;
    return 0;
}