#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;
}

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

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

    return returnValue;
}

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

   while (not goodAnswer) {
       cout << "Do you want to compute another factorial? (yes,no) ";
       cin >>userInput;

       userInput = MakeLower(userInput);

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

   return doContinue;

}

string MakeLower(string word){
   int i;

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

   return word;
}