График функции с использованием WinApi

#include "stdafx.h"
#include <iostream>
#include <string>
#include <Windows.h>
#include <stdlib.h>
#include <math.h>
 
 
 
 
using namespace std;
double a, b;
int n;
double x;
double *mass_of_points;
double *mass_of_function_value;
 
double lagranz(double *mas_of_points, double *mas_of_function_value, double t);
void mass_of_nodes(double a, double b, int n);
void mass_of_value(double *mass_of_points, int n);
double f_x(double a);
 
int main() {
    cout << endl << endl << endl << endl << endl << endl << endl;
    cout << "enter n"<<endl;
    cin >> n;
    cout << "enter a and b"<<endl;
    cin >> a >> b;
    cout << "enter x*"<<endl;
    cin >> x;
    
    mass_of_points = new double[n];
    mass_of_function_value = new double[n];
 
    mass_of_nodes(a, b, n);
    mass_of_value(mass_of_points, n);
 
    
 
    for (int i = 0; i < n; i++) {
        cout <<i+1<< ")  x= " << mass_of_points[i] << "; f(x)=" << mass_of_function_value[i] << endl;
    }
    cout << "p"<<n<<"(x*)=" << lagranz(mass_of_points, mass_of_function_value,x )<< " " << endl;
    
    float x;
    HDC hDC = GetDC(GetConsoleWindow());
    HPEN Pen = CreatePen(PS_SOLID, 2, RGB(255, 255, 255));
    SelectObject(hDC, Pen);
    MoveToEx(hDC, 0, 85, NULL);
    LineTo(hDC, 200, 85);
    MoveToEx(hDC, 100, 0, NULL);
    LineTo(hDC, 100, 170);
    for (x = -8.0f; x <= 8.0f; x += 0.01f) // O(100,85) - center
    {
        MoveToEx(hDC, 100 * x + 100, -100 * f_x(x) + 85, NULL);//10 - scale
        LineTo(hDC, 100 * x + 100, -100 * f_x(x) + 85);
    }
    for (x = -8.0f; x <= 8.0f; x += 0.01f) // O(100,85) - center
    {
        MoveToEx(hDC, 100 * x + 100, -100 * lagranz(mass_of_points, mass_of_function_value, x) + 85, NULL);//10 - scale
        LineTo(hDC, 100 * x + 100, -100 * lagranz(mass_of_points, mass_of_function_value, x) + 85);
    }
    system("pause");
    return 0;
    return 0;
}
 
double lagranz(double *mas_of_points, double* mas_of_function_value, double t) {
    double z, p1, p2;
    z = 0;
    for (int j = 0; j<n; j++) {
        p1 = 1; p2 = 1;
        for (int i = 0; i<n; i++) {
            if (i == j) {
                p1 = p1 * 1; p2 = p2 * 1;
            }
            else {
                p1 = p1*(t - mas_of_points[i]);
                p2 = p2*(mas_of_points[j] - mas_of_points[i]);
            }
        }
        z = z + mas_of_function_value[j] * p1 / p2;
    }
    return z;
}
 
double f_x(double a) {
    return (1/(1+(25*a*a)));
}
double h;
void mass_of_nodes(double a,double b,int n) {
    h = ((b-a)/(n-1));
    for (int i = 0; i < n; i++) {
        mass_of_points[i] = (a + (i*h));        
    }
};
void mass_of_value(double *mass_of_points,int n) {
    
    for (int i = 0; i < n; i++) {
            mass_of_function_value[i] = f_x(mass_of_points[i]);
    }
};