check later

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

int main()
{
    long double x;
    printf("x> ");
    scanf("%Lf", &x);

    if (fabsl(x) >= 0.5)
    {
        printf("x must be < 0.5, aborted.");
        return 0;
    }

    long double S = 0;
    long double epsilon = 1e-4;

    long double diff;

    int it = 0;    //Now iteration

    do
    {
        diff = (1 + (pow(-1, it) * pow(2, it + 1))) * powl(x, it);
        S += diff;
        //printf("%Lf\n", diff);

        it++;
    }while(fabsl(diff) > epsilon);

    printf("S: %Lf", S);

    return 0;
}