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 */
}