Integral I (método retangular)

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

#define N 1000

double f(double x)
{
    return 1/x;
}

int main(void)
{
    int i;
    double h,soma=0.0f;

    h=(1.0-0.1)/N;

    for (i=0;i<N;i++)
    {
        double x = 0.1 + h*i;
        soma += h*f(x);
    }

    double e = fabs((-log(0.1)-soma)/-log(0.1));

    printf("Valor calculado: %.15e \nValor real: %.15e \n",soma,-log(0.1));
    printf("Erro: %e % \n",e*100);

    return 0;
}

// I(a,b) = h*sum_i ( f(x_i) )
// erro = h/2 * [f(b)-f(a)]
// erro ~ 1/N