t1.c

#include <stdio.h>

#define abs(x) ((x)<0 ? -(x) : (x))

double calc_prec(double x, double pr)
{
    double s = 0;
    double n = 1;
    double k = 1;
    double xx = x;
    if ((x > -1) && (x <= 1)) {
        
        double a = xx / n;
        while (abs (a) > pr) {
            //printf("%f\n", s);
            s = s + k * a;
            xx = xx * x;
            n = n + 1;
            k = -k;
            a = xx / n;
        }
    }
    return s;
}

int main()
{
   printf("%f\n", calc_prec(0.5, 0.0001));
   return 0;
}