Multiplying polynomials maintained as Linked List in C

#include <stdio.h>
#include <conio.h>
#include <malloc.h>
#include <windows.h>
/* structure representing a node of a linked list. The node can store a term of
    a polynomial */
struct polynode
{
 float coeff ;
 int exp ;
 struct polynode *link ;
} ;
void poly_append ( struct polynode **, float, int ) ;
void display_poly ( struct polynode * ) ;
void poly_multiply ( struct polynode *, struct polynode *, struct polynode ** ) ;
void padd ( float, int, struct polynode ** ) ;
int main( )
{
 struct polynode *first, *second, *mult ;
 int i = 1 ;
 first = second = mult = NULL ;  /* empty linked lists */
 poly_append ( &first, 3, 5 ) ;
 poly_append ( &first, 2, 4 ) ;
 poly_append ( &first, 1, 2 ) ;
 system ( "cls" ) ;
 display_poly ( first ) ;
 poly_append ( &second, 1, 6 ) ;
 poly_append ( &second, 2, 5 ) ;
 poly_append ( &second, 3, 4 ) ;
 printf ( "\n\n" ) ;
 display_poly ( second ) ;
 printf ( "\n" ) ;
 while ( i++ < 79 )
  printf ( "-" ) ;
 poly_multiply ( first, second, &mult ) ;
 printf ( "\n\n" ) ;
 display_poly ( mult ) ;
 return 0 ;
}
/* adds a term to a polynomial */
void poly_append ( struct polynode **q, float x, int y )
{
 struct polynode *temp ;
 temp = *q ;
 /* create a new node if the list is empty */
 if ( *q == NULL )
 {
  *q = ( struct polynode * ) malloc ( sizeof ( struct polynode ) ) ;
  temp = *q ;
 }
 else
 {
  /* traverse the entire linked list */
  while ( temp -> link != NULL )
   temp = temp -> link ;
  /* create new nodes at intermediate stages */
  temp -> link = ( struct polynode * ) malloc ( sizeof ( struct polynode ) ) ;
  temp = temp -> link ;
 }
 /* assign coefficient and exponent */
 temp -> coeff = x ;
 temp -> exp = y ;
 temp -> link = NULL ;
}
/* displays the contents of linked list representing a polynomial */
void display_poly ( struct polynode *q )
{
 /* traverse till the end of the linked list */
 while ( q != NULL )
 {
  printf ( "%.1f x^%d  :  ", q -> coeff, q -> exp ) ;
  q = q -> link ;
 }
 printf ( "\b\b\b " ) ;  /* erases the last colon(:) */
}
/* multiplies the two polynomials */
void poly_multiply ( struct polynode *x, struct polynode *y,
       struct polynode **m )
{
 struct polynode *y1 ;
 float coeff1 ;
 int exp1 ;
 y1 = y ;  /* point to the starting of the second linked list */
 if ( x == NULL && y == NULL )
  return ;
 /* if one of the list is empty */
 if ( x == NULL )
  *m = y ;
 else
 {
  if ( y == NULL )
   *m = x ;
  else  /* if both linked lists exist */
  {
   /* for each term of the first list */
   while ( x != NULL )
   {
    /* multiply each term of the second linked list with a
        term of the first linked list */
    while ( y != NULL )
    {
     coeff1 = x -> coeff * y -> coeff ;
     exp1 = x -> exp + y -> exp ;
     y = y -> link ;
     /* add the new term to the resultant polynomial */
     padd ( coeff1, exp1, m ) ;
    }
    y = y1 ;  /* reposition the pointer to the starting of
       the second linked list */
    x = x -> link ;  /* go to the next node */
   }
  }
 }
}
/* adds a term to the polynomial in the descending order of the exponent */
void padd ( float c, int e, struct polynode **s )
{
 struct polynode *r = NULL, *temp = *s ;
 /* if list is empty or if the node is to be inserted before the first node */
 if ( *s == NULL || e > ( *s ) -> exp )
 {
  *s = r = ( struct polynode * ) malloc ( sizeof ( struct polynode ) ) ;
  ( *s ) -> coeff = c ;
  ( *s ) -> exp = e ;
  ( *s ) -> link = temp ;
 }
 else
 {
  /* traverse the entire linked list to search the position to insert a new
   node */
  while ( temp != NULL )
  {
   if ( temp -> exp == e )
   {
    temp -> coeff += c ;
    return ;
   }
   if ( temp -> exp > e && ( temp -> link == NULL ||
         temp -> link -> exp < e ) )
   {
    r = ( struct polynode * ) malloc ( sizeof ( struct polynode ) ) ;
    r -> coeff = c ;
    r -> exp = e ;
    r -> link = temp -> link ;
    temp -> link = r ;
    return ;
   }
   temp = temp -> link ;  /* go to next node */
  }
  r -> link = NULL ;
  temp -> link = r ;
 }
}