/*
Title:   /*
Title:   Vectors.c
Author:  Xiaoyang Yu
Revised: 22-NOV-2002

Module Interface Specification:
INTERFACE Vectors;
TYPE  vector;
CONST zero: vector;
PROCEDURE getvec(x,y: float): vector;
PROCEDURE xval(v: vector): float;
PROCEDURE yval(v: vector): float;
PROCEDURE add(u,v: vector): vector;
PROCEDURE mul(r: float; v: vector): vector;
END Vectors.
*/

#include "stdio.h"
#include "stdlib.h"
#include "string.h"

#include "vectors.h"

struct rec{
    float  x,y;
    struct rec  *next;
};

vector head = NULL;

/* return the pointer of vector ( x, y ) */
vector getvec(float x, float y)
{
 vector before, after, v;
  
  before = NULL;                                         
  after = head;
  
  /* find where to insert new vector */
  while ( after != NULL && ((x > after->x) || (x == after->x && y > after->y)) )
  {
    before = after;
    after = after->next;
  }
  
  /* vector already in list */
  if ( after != NULL && (x == after->x  && y == after->y) )  
   return after;
 
  /* create new vector */
  v = (struct rec *)malloc(sizeof(struct rec));
  v->x = x;
  v->y = y;    
  v->next = after;
  
  /* update pointer in list */
  if ( before != NULL )
    before->next = v;
  else
    head = v;
  
  return v;
} /* end getvec */


/* return xval of vector v */
float xval(vector v)
{
  return v->x;
} /* end xval */

/* return yval of vector v */
float yval(vector v)
{
  return v->y; 
} /* end yval */

/* add vector u and vector v */
vector add(vector u,vector v)
{
 float x,y;

   x = u->x + v->x;
   y = u->y + v->y;
  
   return getvec(x,y);
} /* end add */

/* multiple r and vector v */
vector mul(float r,vector v)
{
 float  x,y;

   x = v->x * r;
   y = v->y * r;
   
   return getvec(x,y);
} /* end mul */

/* show linklist:test only,delete later */
void showlist()
{
  vector ptr;
  
  printf("\n*** the following is the ordered linklist ***\n\n");

  ptr = head;	
  while ( ptr != NULL )
  {
    if( ptr->next != NULL ) 
       printf("(%f,%f)-->",ptr->x,ptr->y);
    else 
       printf("(%f,%f)\n",ptr->x,ptr->y);
    
    ptr = ptr->next;  
  }
} /* end showlist */

/* the end of vectors.c */