Question during complex number structure implementation! c2039 Error

#include<stdio.h>
#include<math.h>

struct complex
{
    double real;
    double imag;
};

void add(struct complex* p, struct complex* q, struct complex* r);
void multiply(struct complex* p, struct complex* q, struct complex* r);
int main()
{
    struct complex p;
    struct complex q;
    struct complex r;
    scanf("%lf %lf", p.real, p.imag);
    scanf("%lf %lf", q.real, q.imag);
    add(&p, &q, &r);
    multiply(&p, &q, &r);
}

void add(struct complex* p, struct complex* q, struct complex* r)
{
    r->real = p->real + q->real;
    r->imag = p->imag + q->imag;
    printf("%lf %lf", r->real, r->imag);
}

void multiply(struct complex* p, struct complex* q, struct complex* r)
{
    r->real = ((p->real) * (q->real)) - ((p->imag) * (q->imag));
    r->imag = ((p->real) * (q->imag)) - ((p->imag) * (q->real));
    printf("%lf %lf", r->real, r->imag);
}