double sum(double a[], unsigned int alen) {
        // double* a  is equivalent
    double res = 0;
    unsigned int i;

    for (i = 0; i < alen; i++) {
        res += a[i];
            // *(a + i)  is equivalent
    }

    return res;
}

void foo() {
    double xs[] = {10, 20, 30.5};
    double s = sum(xs, 3);
}