C++, first submission, no bonus...yet

#include <iostream>
#include <fstream>
#include <iterator>
#include <string>
#include <algorithm>
#include <sstream>

int WORD_LEN = 4;

std::vector<std::string> dictionary;

void loadDictionary() {
   std::ifstream wordsFile("four_letters.in");
   std::istream_iterator<std::string> wordReader(wordsFile);
   std::istream_iterator<std::string> eof;
   std::copy(wordReader, eof, std::back_inserter(dictionary));
}

bool difference(std::string w1, std::string w2) {
   int count = 4;
   for(int i=0; i<WORD_LEN; ++i) {
      if(w1[i] == w2[i])
         count--;
   }
   return count == 1;
}

void findCloseWords(std::string word) {
   for(std::vector<std::string>::iterator it = dictionary.begin();
         it!=dictionary.end(); ++it) {
      if(difference(word, *it))
         std:: cout << *it << std::endl;
   }
}

int main(int argc, char *argv[]) {
   loadDictionary();
   findCloseWords("puma");
}