Thread: Structures?

Originally Posted by lilywest

Would you use all "->" instead of "." because when I do that I get:
hw12.c:55: error: invalid type argument of '->'
hw12.c:55: error: invalid type argument of '->'
hw12.c:55: error: invalid type argument of '->'

Clearly not, since you are getting all those errors.

If you have a pointer to a struct, use -> to access a member
If you have a plain struct, use . to access a member:

Is random a pointer to struct? Yes, so use -> to get vertex.
Is vertex[0] a pointer to struct? No, so use . to get x or y.

update:
Got rid of those errors, now code looks like:

Code:

  printf ("The triangle:\n");
  printf ("\tVertex[0] is [%.02f, %.02f]\n", random.vertex[0].x, random.vertex[0].y);
  printf ("\tVertex[1] is [%.02f, %.02f]\n", random.vertex[1].x, random.vertex[1].y);
  printf ("\tVertex[2] is [%.02f, %.02f]\n", random.vertex[2].x, random.vertex[2].y);
  struct point centroid;
  printf ("\nThe centroid is: [%.02f, %.02f]\n", calcCentroid(centroid.x), i);
}

struct triangle calcCentroid (struct triangle *random)
{
  struct point centroid;
  centroid.x = (random->vertex[0].x + random->vertex[1].x + random->vertex[2].x) / 3;
  centroid.y = (random->vertex[0].y + random->vertex[1].y + random->vertex[2].y) / 3;
  return;
}

and now getting:
hw12.c: In function 'main':
hw12.c:44: error: incompatible type for argument 1 of 'calcCentroid'


as error.

Well, calcCentroid requires a pointer-to-triangle. centroid.x is not a pointer-to-triangle, so that's not what you pass along.

I don't think I understand what you're getting at... I changed the function header to:

Code:

struct point calcCentroid (struct triangle *random)

and left everything else the same but still I'm getting the same error. I'm sorry I'm not getting it!

Well that's what you originally had, isn't it?

Anyway, in order to calculate the Centroid of a triangle you need (unsurprisingly) a triangle, not a random point that you've picked from somewhere. You have to call this function with a triangle.