#include <iostream>
#include <string>

using namespace std;

int Factorial(int n);
bool AskUserToContinue(void);
string MakeLower(string word);

int main () {

    int i {4};

    bool keepGoing {true};

    while (keepGoing) {
        cout << i << "! = " << Factorial(i) << endl;

        keepGoing = AskUserToContinue();
    }


    return 0;
}

bool AskUserToContinue(void){
   string userResponse;
   bool doContinue;
   bool goodAnswer{false};

   while(not goodAnswer) {
       cout <<"Do you wish to continue (yes, no) => ";
       cin >> userResponse;

       userResponse = MakeLower(userResponse);

       if (userResponse == "yes") {
          doContinue = true;
          goodAnswer = true;
       } else if (userResponse == "no") {
          doContinue = false;
          goodAnswer = true;
       } else {
          cout << "Please enter yes or no!" << endl; 
       }
   }
   return doContinue;

}

int Factorial(int n){
   int i;
   int returnValue{1};

   for(i=2; i <= n; ++i) {
      returnValue *= i;
   }

   return returnValue;

}

string MakeLower(string word){
   int i;
   for(i =0; i < word.size(); ++i) {
      word[i] = tolower(word[i]);
   }

   return word;
}