Add two polynomials maintained as linked lists

C: Program to add two polynomials maintained as linked lists.

#include <stdio.h>
#include <conio.h>
#include <alloc.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 ** ) ;

void main( )
{
    struct polynode *first, *second, *total ;
    int i = 0 ;

    first = second = total = NULL ;  /* empty linked lists */

    poly_append ( &first, 1.4, 5 ) ;
    poly_append ( &first, 1.5, 4 ) ;
    poly_append ( &first, 1.7, 2 ) ;
    poly_append ( &first, 1.8, 1 ) ;
    poly_append ( &first, 1.9, 0 ) ;

    clrscr( ) ;
    display_poly ( first ) ;

    poly_append ( &second, 1.5, 6 ) ;
    poly_append ( &second, 2.5, 5 ) ;
    poly_append ( &second, -3.5, 4 ) ;
    poly_append ( &second, 4.5, 3 ) ;
    poly_append ( &second, 6.5, 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 */
}

/* 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 = 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 = 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 = malloc ( sizeof ( struct polynode ) ) ;
            z = *s ;
        }
        /* create new nodes at intermediate stages */
        else
        {
            z -> link = 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 = malloc ( sizeof ( struct polynode ) ) ;
            z = *s ;
        }
        else
        {
            z -> link = 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 = malloc ( sizeof ( struct polynode ) ) ;
            z = *s ;
        }
        else
        {
            z -> link = 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 */
}