Code

 Header...
#define PI 3.14159265358979
typedef struct ellipse {
  float centre[2];
  float axes[2];
  float orientation;
  float area;
}Ellipse;

void calculate_area (Ellipse *el);
void read_ellipse (Ellipse *el);
void resize_ellipse (Ellipse *el,float scale);
void move_ellipse (Ellipse *el,float dx[2]);

 int main(){
   ... 

»  float moveby[2], resize;
»  Ellipse *e=NULL;

»  e=malloc(sizeof *e);
»  if (e==NULL) {
»    fprintf(stderr, "Out of memory\n");
»    exit(99);
  }
  
»  printf("Welcome to the ellipse program\n");
»  read_ellipse(e);
  
»  printf("The area of the ellipse is: %f\n", e->area);
  
»  printf("Amount to move the ellipse?\n");
»  scanf("%g %g", &moveby0, &moveby1);
  
»  move_ellipse(e, moveby);
  
»  printf("Amount to resize the ellipse?\n");
»  scanf("%g", &resize);
  
»  resize_ellipse(e, resize);
  
»  return 0;
}

 void read_ellipse(Ellipse *el){
   ... 


»  printf("Centre? (x,y)\n");
»  scanf("%f %f", &el->centre[0], &el->centre[1]);

»  printf("Length of axes ( > 0 )?\n");
»  scanf("%f %f", &el->axes[0], &el->axes[1]);

»  printf("Orientation to the vertical?\n");
»  scanf("%f", &el->orientation);

»  calculate_area(el);// Pass the pointer to another function
}

// Resize an ellipse by the same scaling factor in each dimension.
 void resize_ellipse(Ellipse *el,float scale){
   ... 

»  el->axes0*=scale;
»  el->axes1*=scale;
»  calculate_area(el);
}

// Calculate the area of an ellipse and save it in the structure
 void calculate_area(Ellipse *e){
   ... 

»  e->area=PI*e->axes[0]*e->axes[1];
}

 void move_ellipse(Ellipse *el,float dx[2]){
   ... 

»  el->centre0+=dx0;
»  el->centre1+=dx1;
}