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

using namespace std;

void typing();
void reading();
double chkdsk();
int choice;
int n;
double x;
double y;
double a, b, h;
double greater();

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 */
	{
		typing();
		chkdsk();
		goto next;
	}
	case 2: /* Input data from file and calculate result */
	{
		reading();
		chkdsk();
		goto next;
	}
	case 3: /* That what lets you to output your data to a certain directory */
	{
		ofstream file("output.txt", ios::app);
		file << "x = " << x << "\n" << "y = " << y << endl;
		cout << "Writing this to a file..." << endl;
		Sleep(1000);
		file.close();
	}
	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:
		cout << "\nNot a valid choice \n" << "Choose again \n";
		goto next;
		system("pause");
	}
}

double chkdsk()
{
	try
	{
		if (n < 4)
		{
			throw "error";
		}
		else
		{
			for (x = a; x <= b; x = x + h)
			{
				if (x >= 0)
				{
					y = 0;
					greater();
					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;
					}
				}
				if (x < 0)
				{
					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;
}

double greater()
{
	try
	{
		if (a > b)
		throw a;
	}
	catch (double)
	{
		cout << "\nA must be greater than B\n";
		return 0;
	}
}

void reading()
{
	ifstream file("input.txt", ios::app);
	file >> a >> b >> h >> n;
}

void typing()
{
	cout << "Type a, b, h, n: " << endl;
	cin >> a >> b >> h >> n;
}