#define trapezoid_area(h, total_bases_len) ((h) * (total_bases_len) / 2)

int main(void)
{
    float h = 10.0;
    float b = 20.0;
    float B = 30.0;
    float area = trapezoid_area(h, b + B); // se expandează la: ((h) * (b + B) / 2)
    ...
    return 0;
}