/**
 * @file pi.cpp
 * @brief Calculates pi for the given number of terms
 * @author syb0rg
 * @date 10/3/14
 */

#include <iostream>
#include <limits>
#include <cctype>
#include <cmath>

/**
 * Makes sure data isn't malicious, and signals user to re-enter proper data if invalid
 */
void getSanitizedDouble(long double &input)
{
    while (!(input = std::cin.peek()) && input != 'n')
    {
        if (std::isalpha(input) || std::isspace(input)) std::cin.ignore(); // ignore alphabetic and space characters from input
    }
    while(!(std::cin >> input) || input < 0)
    {
        std::cin.clear(); // clear the error flag that was set so that future I/O operations will work correctly
        std::cin.ignore(std::numeric_limits<std::streamsize>::max(), 'n'); // skips to the next newline
        std::cout << "Invalid input.  Please enter a positive number: ";
    }
}

int main()
{
    long double num = 0.;
    char again = '';
    do
    {
        long double pi = 0.;

        // get input for height, re-read input if not a positive number
        std::cout << "Enter the number of terms to approximate π: ";
        getSanitizedDouble(num);

        for(auto i = 0; i < num; i++)
        {
            pi += std::pow(-1, i) / (2 * i + 1);
        }
        pi *= 4;

        std::fprintf(stdout, "Approximated value of π for %Lg terms: %Lgn", num, pi);

        std::cout << "Run the program again (y/N): ";  // signify n as default with capital letter
        std::cin.get();  // absorb newline character from previous input
        std::cin.get(again);
        again = std::tolower(again);
    } while (again == 'y');
}