I need help implementing explicit runge kutta method into this c++ .cpp file.

ExplicitRKScheme:: ExplicitRKScheme (int s, const double *aa const double *ww const double *cc) {stage = s; a = aa; w = ww; c = cc; k.resize (s);} double ExplicitRKScheme:: one_step_march (double h, double tau, double ytau) {double ytauplush;//implement here return ytauplush;}