Interfacing C++ functions (1)

This is like interfacing C functions, except that pointers are usual replaced by references

void hw3(double r1, double r2, double *s)  // C style
{ *s = sin(r1 + r2); }

void hw4(double r1, double r2, double& s)  // C++ style
{ s = sin(r1 + r2); }