#include <stdio.h>
#include <conio.h>

#define MAX 10

struct term
{
    int coeff ;
    int exp ;
} ;

struct poly
{
    struct term t [10] ;
    int noofterms ;
} ;

void initpoly ( struct poly *) ;
void polyappend ( struct poly *, int, int ) ;
struct poly polyadd ( struct poly, struct poly ) ;
struct poly polymul ( struct poly, struct poly ) ;
void display ( struct poly ) ;

void main( )
{
    struct poly p1, p2, p3 ;

    clrscr( ) ;

    initpoly ( &p1 ) ;
    initpoly ( &p2 ) ;
    initpoly ( &p3 ) ;

    polyappend ( &p1, 1, 4 ) ;
    polyappend ( &p1, 2, 3 ) ;
    polyappend ( &p1, 2, 2 ) ;
    polyappend ( &p1, 2, 1 ) ;

    polyappend ( &p2, 2, 3 ) ;
    polyappend ( &p2, 3, 2 ) ;
    polyappend ( &p2, 4, 1 ) ;

    p3 = polymul ( p1, p2 ) ;

    printf ( "\nFirst polynomial:\n" ) ;
    display ( p1 ) ;

    printf ( "\n\nSecond polynomial:\n" ) ;
    display ( p2 ) ;

    printf ( "\n\nResultant polynomial:\n" ) ;
    display ( p3 ) ;

    getch( ) ;
}

/* initializes elements of struct poly */
void initpoly ( struct poly *p )
{
    int i ;
    p -> noofterms = 0 ;
    for ( i = 0 ; i < MAX ; i++ )
    {
        p -> t[i].coeff = 0 ;
        p -> t[i].exp = 0 ;
    }
}

/* adds the term of polynomial to the array t */
void polyappend ( struct poly *p, int c, int e )
{
    p -> t[p -> noofterms].coeff = c ;
    p -> t[p -> noofterms].exp =  e ;
    ( p -> noofterms ) ++ ;
}

/* displays the polynomial equation */
void display ( struct poly p )
{
    int flag = 0, i ;
    for ( i = 0 ; i < p.noofterms ; i++ )
    {
        if ( p.t[i].exp != 0 )
            printf ( "%d x^%d + ", p.t[i].coeff, p.t[i].exp ) ;
        else
        {
            printf ( "%d", p.t[i].coeff ) ;
            flag = 1 ;
        }
    }
    if ( !flag )
        printf ( "\b\b  " ) ;

}
/* adds two polynomials p1 and p2 */
struct poly polyadd ( struct poly p1, struct poly p2 )
{
    int i, j, c ;
    struct poly p3 ;
    initpoly ( &p3 ) ;

    if ( p1.noofterms > p2.noofterms )
        c = p1.noofterms ;
    else
        c = p2.noofterms ;

    for ( i = 0, j = 0 ; i <= c ; p3.noofterms++ )
    {
        if ( p1.t[i].coeff == 0 && p2.t[j].coeff == 0 )
            break ;
        if ( p1.t[i].exp >= p2.t[j].exp )
        {
            if ( p1.t[i].exp == p2.t[j].exp )
            {
                p3.t[p3.noofterms].coeff = p1.t[i].coeff + p2.t[j].coeff ;
                p3.t[p3.noofterms].exp = p1.t[i].exp ;
                i++ ;
                j++ ;
            }
            else
            {
                p3.t[p3.noofterms].coeff = p1.t[i].coeff ;
                p3.t[p3.noofterms].exp = p1.t[i].exp ;
                i++ ;
            }
        }
        else
        {
            p3.t[p3.noofterms].coeff = p2.t[j].coeff ;
            p3.t[p3.noofterms].exp = p2.t[j].exp ;
            j++ ;
        }
    }
    return p3 ;
}

/* multiplies two polynomials p1 and p2 */
struct poly polymul ( struct poly p1, struct poly p2 )
{
    int coeff, exp ;
    struct poly temp, p3 ;

    initpoly ( &temp ) ;
    initpoly ( &p3 ) ;

    if ( p1.noofterms != 0 && p2.noofterms != 0 )
    {
        int i ;
        for ( i = 0 ; i < p1.noofterms ; i++ )
        {
            int j ;

            struct poly p ;
            initpoly ( &p ) ;

            for ( j = 0 ; j < p2.noofterms ; j++ )
            {
                coeff = p1.t[i].coeff * p2.t[j].coeff ;
                exp = p1.t[i].exp + p2.t[j].exp ;
                polyappend ( &p, coeff, exp ) ;
            }

            if ( i != 0 )
            {
                p3 = polyadd ( temp, p ) ;
                temp = p3  ;
            }
            else
                temp = p ;
        }
    }
    return p3 ;
}