Método de Euler II (+ fprintf)

#include <stdio.h>
#include <math.h>

#define dt 1e-2

#define x0 0
#define t0 0
#define tf 10

#define N ((tf-t0)/dt)

double dxdt(double x, double t)
{
    return -x*x*x + sin(t);
}

int main(void)
{
    double x = x0, xn, t = t0, tn;
    int i;

    FILE *h = fopen("./euler.dat","w+");

    for (i = 0; i < N; ++i)
    {
        xn  = x + dxdt(x,t)*dt;
        tn = t + dt;
        fprintf(h, "%d %f %f\n", i, t, x);
        x = xn;
        t = tn;
    }

    fclose(h);
    return 0;
}