// collatzfile.cpp
// Andrew Cummins
// 21 Oct 2016
// Program that will take users input of two integers and write collatz sequence between the two integers in a txt file

#include <iostream>
using std::cout;
using std::endl;
using std::cin;
#include <string>
using std::string;
using std::getline;
#include <sstream>
using std::istringstream;
#include <fstream>
using std::ofstream;

//function to handle the math and write to the file
int collatz(int n)
{
    // use ios_base::app to append the file instead of overwriting
    ofstream outfile("cseqs.txt", std::ios_base::app);
    if(!outfile)
    {
        // check if the file opened
        cout << "Could not open file" << endl;
        return 0;
    }
    outfile << n;
    while(n>1)
    {
        if(n%2==0)
        {
            n=n/2;
            outfile << ", " << n;
        }
        else
        {
            n=n*3+1;
            outfile << ", " << n;
        }
    }
    outfile << endl << endl;
}

int main()
{
    // loop to keep asking user for input
    while(true)
    {
        // ask for first integer
        cout << "Enter the first integer to begin a Collatz sequence: ";
        int number1;
            cin >> number1;
            if(!cin){ // error check
              return 0;
            }
            if(number1<0){ // make sure it is not negative
                cout << "Must be a positive number" << endl;
                continue;
            }
        cout << endl << endl;
        // ask for last integer
        cout << "Enter the last integer to begin a Collatz sequence: ";
        int number2;
            cin >> number2;
            if(!cin){ // error checking
              return 0;
            }
            if(number2<0){// make sure it is not negative
                cout << "Must be a positive number" << endl;
                continue;
            }
        cout << endl << endl;
        // make sure last integer is larger than first
        if(number1>number2)
        {
            cout << "The second integer must be at least as large as the first: try again" << endl;
            continue;
        }
        else
        {
            cout << endl << endl;
            cout << "Sequence beginning at " << number1 << " ... " << number2 << " successfully written to file 'cseqs.txt'" << endl;
            cout << endl << endl;
            // send each integer in the range to the function
            for(int i=number1; i<=number2; ++i)
            {
                collatz(i);
            }
            return 0; // end program once file is written
        }
    }
}