// Recursion Assignment
// Proving whether or not a string of characters is a WFF
// Justin McCreary
// Instructor: Mrs. Ames
// 11/4/08

#include <iostream>
using namespace std;

//-----------------------------------------------------------------------------
// WFFCatcher inputs one character at a time until it returns a true or false 
// statement, upon which the code checks whether or not it is a WFF.
//-----------------------------------------------------------------------------

bool WFFCatcher()
{
	char ch;
	cin.get(ch); //inputs character
	if( ch == 'p' || ch == 'q' || ch == 'r' || ch == 's' )
	{
		return true; //base case 1
	}
	else if ( ch == 'N' )
	{
		return WFFCatcher(); //general case
	}
	else if (ch == 'C' || ch == 'A' || ch == 'K' || ch == 'E')
	{
		return WFFCatcher() && WFFCatcher(); //general case
	} 
	else
	{
		return false;  //base case 2
	}
	
}

int main ()
{
   bool W = true;
   char ch;
   cout << "Enter a string to determine whether or not it is WFF : ";

   W = WFFCatcher(); //Asks for a true or false statement
   cin.get(ch); 
   if ( W == true) //Checks whether or not true
   {    // if true, checks whether or not it went through the entire string
	if(ch != '\n')
		cout << "Not a WFF.\n";
	else
		cout << "A WFF.\n";
   }
   // if false, outputs this statement
   else 
	cout << "Not a WFF.\n";
   
   return 0;
}