formysun

#include <iostream>
#include <fstream>
#include <string>
using namespace std;

double function(double t, double u)
{
    return 4 / (t * t) - (u / t) - (u * u);
}
void priblizhennoe(ofstream&out, double h, double N, double t0, double U0)
{
    double t, u, f, k1, k2, k3, k4;
    u = U0;
    t = t0;
    //cout << "Для t0 = " << t << " U0 = " << u << "\n";
    out << u << "\n";
    for (int i = 0; i < N; i++)
    {
        k1 = function(t, u);
        k2 = function(t + h / 2, u + (h * k1) / 2);
        k3 = function(t + h / 2, u + (h * k2) / 2);
        k4 = function(t + h, u + h * k3);
        u += h * (k1 + (2 * k2) + (2 * k3) + k4) / 6;
        t += h;
        //cout << "При t" << i + 1 << " = " << t << " U" << i + 1 << " равно: " << u << "\n";
        out << u << "\n";
    }
}
void tochnoe(double N, double h, double t0, double U0, double C)
{
    double t, u;
    t = t0;
    u = U0;
    cout << "При t" << 0 << " = " << t << " U" << 0 << " = " << u << "\n";
    for (int i = 0; i < N; i++)
    {
        t = t + h;
        u = (2 * (t * t * t * t + C)) / (t * (t * t * t * t - C));
        cout << "При t" << i + 1 << " = " << t << " U" << i + 1 << " = " << u << "\n";
    }
}
int main()
{
    ofstream out("pribresh.txt");
    setlocale(LC_ALL, "RU");
    double t0, T, h, N, U0;
    cout << "Введите область [to,T]:\n";
    cin >> t0 >> T;
    cout << "Введите N и U0: ";
    cin >> N >> U0;
    h = (T - t0) / N;
    double C;
    C = (t0 * t0 * t0 * t0 * (t0 * U0 - 2)) / (2 + U0 * t0);
    //cout << "Приближенные решения: \n";
    priblizhennoe(out, h, N, t0, U0);
    out.close();
    //cout << "Точные решения: \n";
    //tochnoe(N, h, t0, U0);
    ifstream inout("pribresh.txt");
    ofstream outn100("n100.txt");
    string s;
    while (inout.peek() != EOF)
    {
        inout >> s;
        for (int i = 0; i < s.length(); i++)
            if (s[i] == '.')
                s[i] = ',';
        outn100 << s << "\n";
    }
    inout.close();
    outn100.close();

    return 0;
}