Практика - задание 2

#define _CRT_SECURE_NO_WARNINGS
#include "graphics.h"
#include <iostream>
#include <math.h>
#include <cstdlib>
#include <string>
#include <fstream>

using namespace std;

double func(double x); //Вычисляет значение функции f(x)=x*e^(x)*sin(x)

double f2(double x, double h); //Вторая производная

int main(int argc, char * argv[])
{
	int n = 48;
	double a = 0, b = 1, h1, e = 0.001, S, f2max;
	double i;
	int w = 1900, h = 1000;
	int height = h - 100;
	int length = w - 50;
	setlocale(LC_ALL, "RUSSIAN");
	cout << "Нахождение определенного интеграла функции f(x)=x*e^(x)*sin(x) на отрезке [0;1]. Отрезок разбивается на 48 частей." << endl;
	while (1)
	{
		h1 = (b - a) / n;
		S = h1 * (func(a) + func(b)) / 2;
		for (i = 0; i < n; i++)
		{
			S = S + func(a + h1 * i)*h1;
		}
		f2max = f2(a, h1);
		for (i = 0; i < n; i++)
		{
			if (f2(a + h1 * i, h1) > f2max) f2max = f2(a + h1 * i, h1);
		}
		double check = f2max * pow(b - a, 3) / (12 * n*n);
		if (check > e)
		{
			n = n + 5;
		}
		else
		{
			cout << "Значение интеграла = " << S << endl;
			break;
		}

	}
	cout << "Нажмите Enter, чтобы вывести диаграмму." << endl;
	system("pause");
	int mastx = length / n;
	double maxfunc = func(a);
	for (i = 1; i < n; i++)
	{
		if (func(a + i * h1) > maxfunc)
			maxfunc = func(a + i * h1);
	}
	if (func(b) > maxfunc)
		maxfunc = func(b);
	int masty = height / maxfunc;
	char conv[128];
	initwindow(w, h, "Diagrama");
	bar(0, 0, w, h);
	rectangle(0, 0, w, h);
	setcolor(0);
	setbkcolor(15);

	line(30, 30, 30, 30 + height);
	line(30, 30, 25, 40);
	line(30, 30, 35, 40);
	line(30, 30 + height, 20 + length, 30 + height);
	line(20 + length, 30 + height, length + 15, 25 + height);
	line(20 + length, 30 + height, length + 15, 35 + height);
	outtextxy(length + 20, 45 + height, "x");
	outtextxy(40, 30, "f(x)");
	for (i = 0; i < 1; i+=0.2)
	{
		line(30 + i * length, 20 + height, 30 + i * length, 40 + height);
		sprintf(conv, "%f", i);
		outtextxy(30 + i * length, 45 + height, conv);
		double k = 30 + height - func(i) * masty;
		line(20, 30 + height - func(i) * masty, 40, 30 + height - func(i) * masty);
		sprintf(conv, "%f", func(i));
		outtextxy(5, 30 + height - func(i) * masty, conv);

	}
	for (i = 0; i < n; i++)
	{
		line(30 + i * mastx, 30 + height, 30 + i * mastx, 30 + height - func(a+i*h1) * masty);
		line(30 + i * mastx, 30 + height - func(a + i * h1) * masty, 30 + (i + 1) * mastx, 30 + height - func(a + i * h1) * masty);
		line(30 + (i + 1) * mastx, 30 + height, 30 + (i + 1) * mastx, 30 + height - func(a + i * h1) * masty);
	}
	getch();
	while (!kbhit())
	{
		delay(200);
	}
	getch();
	closegraph();

	cout << "Нажмите Enter, чтобы вывести график функции." << endl;
	system("pause");
	initwindow(w, h, "Diagrama");
	bar(0, 0, w, h);
	rectangle(0, 0, w, h);
	setcolor(0);
	setbkcolor(15);

	line(30, 30, 30, 30 + height);
	line(30, 30, 25, 40);
	line(30, 30, 35, 40);
	line(30, 30 + height, 20 + length, 30 + height);
	line(20 + length, 30 + height, length + 15, 25 + height);
	line(20 + length, 30 + height, length + 15, 35 + height);
	outtextxy(length + 20, 45 + height, "x");
	outtextxy(40, 30, "f(x)");
	for (i = 0; i < 1; i += 0.2)
	{
		line(30 + i * length, 20 + height, 30 + i * length, 40 + height);
		sprintf(conv, "%f", i);
		outtextxy(30 + i * length, 45 + height, conv);
		double k = 30 + height - func(i) * masty;
		line(20, 30 + height - func(i) * masty, 40, 30 + height - func(i) * masty);
		sprintf(conv, "%f", func(i));
		outtextxy(5, 30 + height - func(i) * masty, conv);

	}
	for (i = 0; i < n; i++)
	{
		line(30 + i * mastx, 30 + height - func(a + i * h1) * masty, 30 + (i + 1) * mastx, 30 + height - func(a + (i+1) * h1) * masty);
	}
	getch();
	while (!kbhit())
	{
		delay(200);
	}
	getch();
	closegraph();
	system("pause");
	return 0;
}
double func(double x) //Вычисляет значение функции f(x)=x*e^(x)*sin(x)
{
	return x * exp(x)*sin(x);
}

double f2(double x, double h) //Вторая производная
{
	return (func(x + h) - 2 * func(x) + func(x - h)) / (h * h);
}