Adding 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 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_add ( struct polynode *, struct polynode *, struct polynode ** ) ;
int main( )
{
 struct polynode *first, *second, *total ;
 int i = 0 ;
 first = second = total = NULL ;  /* empty linked lists */
 poly_append ( &first, 1.4f, 5 ) ;
 poly_append ( &first, 1.5f, 4 ) ;
 poly_append ( &first, 1.7f, 2 ) ;
 poly_append ( &first, 1.8f, 1 ) ;
 poly_append ( &first, 1.9f, 0 ) ;
 system ( "cls" ) ;
 display_poly ( first ) ;
 poly_append ( &second, 1.5f, 6 ) ;
 poly_append ( &second, 2.5f, 5 ) ;
 poly_append ( &second, -3.5f, 4 ) ;
 poly_append ( &second, 4.5f, 3 ) ;
 poly_append ( &second, 6.5f, 1 ) ;
 printf ( "\n\n" ) ;
 display_poly ( second ) ;
 /* draws a dashed horizontal line */
 printf ( "\n" ) ;
 while ( i++ < 79 )
  printf ( "-" ) ;
 printf ( "\n\n" ) ;
 poly_add ( first, second, &total ) ;
 display_poly ( total ) ;  /* displays the resultant polynomial */
 return 0 ;
}
/* adds a term to a polynomial */
void poly_append ( struct polynode **q, float x, int y )
{
 struct polynode *temp ;
 temp = *q ;
 /* creates 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 */
}
/* adds two polynomials */
void poly_add ( struct polynode *x, struct polynode *y, struct  polynode **s )
{
 struct polynode *z ;
 /* if both linked lists are empty */
 if ( x == NULL && y == NULL )
  return ;
 /* traverse till one of the list ends */
 while ( x != NULL && y != NULL )
 {
  /* create a new node if the list is empty */
  if ( *s == NULL )
  {
   *s = ( struct polynode * ) malloc ( sizeof ( struct polynode ) ) ;
   z = *s ;
  }
  /* create new nodes at intermediate stages */
  else
  {
   z -> link = ( struct polynode * ) malloc ( sizeof ( struct polynode ) ) ;
   z = z -> link ;
  }
  /* store a term of the larger degree polynomial */
  if ( x -> exp < y -> exp )
  {
   z -> coeff = y -> coeff ;
   z -> exp = y -> exp ;
   y = y -> link ;  /* go to the next node */
  }
  else
  {
   if ( x -> exp > y -> exp )
   {
    z -> coeff = x -> coeff ;
    z -> exp = x -> exp ;
    x = x -> link ;  /* go to the next node */
   }
   else
   {
    /* add the coefficients, when exponents are equal */
    if ( x -> exp == y -> exp )
    {
     /* assigning the added coefficient */
     z -> coeff = x -> coeff + y -> coeff ;
     z -> exp = x -> exp ;
     /* go to the next node */
     x = x -> link ;
     y = y -> link ;
    }
   }
  }
 }
 /* assign remaining terms of the first polynomial to the result */
 while ( x != NULL )
 {
  if ( *s == NULL )
  {
   *s = ( struct polynode * ) malloc ( sizeof ( struct polynode ) ) ;
   z = *s ;
  }
  else
  {
   z -> link = ( struct polynode * ) malloc ( sizeof ( struct polynode ) ) ;
   z = z -> link ;
  }
  /* assign coefficient and exponent */
  z -> coeff = x -> coeff ;
  z -> exp = x -> exp ;
  x = x -> link ;  /* go to the next node */
 }
 /* assign remaining terms of the second polynomial to the result */
 while ( y != NULL )
 {
  if ( *s == NULL )
  {
   *s = ( struct polynode * ) malloc ( sizeof ( struct polynode ) ) ;
   z = *s ;
  }
  else
  {
   z -> link = ( struct polynode * ) malloc ( sizeof ( struct polynode ) ) ;
   z = z -> link ;
  }
  /* assign coefficient and exponent */
  z -> coeff = y -> coeff ;
  z -> exp = y -> exp ;
  y = y -> link ;  /* go to the next node */
 }
 z -> link = NULL ;  /* assign NULL at end of resulting linked list */
}