#include <iostream>
#include <cmath>
#include <Windows.h>
#include <fstream>
#include <cstdlib>

using namespace std;
using std::cout;

int chkdsk();
int fldsk();
int choice;
int n;
double x;
double y;
double a, b, h;

void main()
{
next:
	bool
	{
		cout << endl
		<< "1. Input data from keyboard and calculate result\n"
		<< "2. Input data from file and calculate result\n"
		<< "3. Save result to file\n"
		<< "4. Help!\n"
		<< "5. Exit program\n"
		<< "\n" << "Make your choice and press 'Enter': "
	};


	cin >> choice;

	switch (choice)
	{
	case 1: /* A line to input data from keyboard and calculate result */
	{
		do chkdsk();
		while (n < 4);
		goto next;
	}
	case 2: /* Input data from file and calculate result */
	{
		fldsk();
		goto next;
	}
	case 3: /* That what lets you to output your data to a certain directory */
	{
		ofstream file("output.txt", ios::out | ios::app);
		file << x << "\n" << y << endl;
		cout << "Writing this to a file..." << endl;
		Sleep(1000);
	}
		goto next;
	case 4: /* Just some additional information – FAQ and Credits */
		int choice_2;
		bool
		{
			cout << "\n" << "1. FAQ\n" << "2. Author credits\n"
		};

		cout << "\n";
		cin >> choice_2;
		cout << "\n";

		switch (choice_2)
		{
		case 1: /* FAQ */
			cout << "\t\t\tFAQ for the main menu\n"
				<< "1. To make input from keyboard and calculate your result, please, press '1'. \n"
				<< "2. To make input from file and calculate the result, press '2'. \n"
				<< "3. To save the result into file, press '3'. \n"
				<< "4. To see some additional information and author credits, press '4'. In the following menu, choose between '1' and '2'. \n"
				<< "5. Press '5' if you want to exit the program. \n";
			cout << endl;
			system("pause");
			goto next;
		case 2: /* Author Credits */
			cout << "The program was written and compiled by Maidebura D., group CS-36zh, 2016.\n";
			cout << endl;
			system("pause");
			goto next;
		}
	case 5: /* Exit from program */
		cout << "\nE"; Sleep(100);	cout << "n"; Sleep(100);	cout << "d"; Sleep(100);
		cout << " o"; Sleep(100);	cout << "f"; Sleep(100);
		cout << " p"; Sleep(100);	cout << "r"; Sleep(200);	cout << "o"; Sleep(200);	cout << "g"; Sleep(200);	cout << "r"; Sleep(200);	cout << "a"; Sleep(200);	cout << "m";
		Sleep(500);
		cout << ".";
		Sleep(500);
		cout << ".";
		Sleep(500);
		cout << ".";
		break;
	default:
		for (choice > 5; choice < 0; )
		{
			cout << "\nNot a valid choice \n"
				<< "Choose again \n";
			main();
			system("pause");
		}
		break;
	}
}
int chkdsk()
{
	double a, b, h;
	cout << "Type a, b, h, n: " << endl;
	cin >> a >> b >> h >> n;
	if (n < 4)
	{
		cout << "error" << endl;
	}
	else
	{
		for (x = a; x <= b; x = x + h)
		{
			if (x >= 0)
			{
				y = 0;
				for (int i = 0; i <= n - 1; i++)
				{
					double z = 1;
					for (int j = 0; j <= n - 1; j++)
					{
						z = z*(x + i + j*j);
					}
					y = y + z;
				}
			}
			else
			{
				y = 1;
				for (int j = 2; j <= n - 2; j++)
				{
					y = y*(j + 1);
				}
			}
			cout << "x = " << x << endl;
			cout << "y = " << y << endl;
		}
	}
	system("pause");
	return (0);
}

int fldsk()
{
	ifstream file("input.txt", ios::app);
	{
		double a, b, h;
		int n;
		file >> a >> b >> h >> n;
		try
		{
			if (n < 4)
			{
				throw n;
			}
			else
			{
				for (x = a; x <= b; x = x + h)
				{
					if (x >= 0)
					{
						y = 0;
						for (int i = 0; i <= n - 1; i++)
						{
							double z = 1;
							for (int j = 0; j <= n - 1; j++)
							{
								z = z*(x + i + j*j);
							}
							y = y + z;
						}
					}
					else
					{
						y = 1;
						for (int j = 2; j <= n - 2; j++)
						{
							y = y*(j + 1);
						}
					}
					cout << "x = " << x << endl;
					cout << "y = " << y << endl;
				}
			}
			cout << endl;
			system("pause");
			return (0);
		}
		catch (double)
		{
			string c = "the value of n must be greater than or equal to 4\n";
			throw c;
			return 0;
		}
	}
}