/* 
 * CSE 303/374 demo program - structs 
 * Basic operations with structs and pointers
 */

/* Struct declaration */

struct Point {
  int x;
  int y;
};


/* basic struct usage */
int main() {
  /* allocate a struct Point */
 struct Point q;
 q.x = 1;
 q.y = 2;

  struct Point p;


  /* set its fields */
  p.x = 4;
  p.y = 3;

  /* read its fields */
  int v = p.x;

  /* pointer to a struct */
  struct Point* r;
  r = &p;

  /* access fields through pointer */
  int cx = (*r).x;
  int cy = r->y;   
  r->y += 2;

}

void print_point(struct Point p) {
  p.x+=1;
  printf("%d %d\n", p.x, p.y);
}


int main() {
  struct Point t;
  print_point(t);
}


/* Point is now a known struct tag, but is _not_ a type  */
/* (could use a typedef if we wanted, but not used here) */

/* Function prototypes */

void init_point(struct Point *p);
struct Point new_point();

/* Function definitions */

void f() {
  struct Point p1, p2;
  init_point(&p1);
  p2 = new_point(); // equivalent, potentially slower
}

void init_point(struct Point *p) {
  p->x = 0;
  (*p).y = 0;
}

struct Point* dangling_point() {
  struct Point ans;
  ans.x = 0;
  ans.y = 0;
  return &ans; // *really* bad idea, later dereference will hopefully crash!
}

struct Point new_point() {
  struct Point ans;
  ans.x = 0;
  ans.y = 0;
  return ans; // no problem
}

void wrong_update_x(struct Point p, int new_x) {
  // this function has no effect on anything
  p.x = new_x;
}


void update_x(struct Point * p, int new_x) {
  // updates field in struct referenced by p
  p->x = new_x;
}