Cộng hai đa thức

#include<stdio.h>
#include<malloc.h>
#include<conio.h>
#include<stdlib.h>
typedef struct dt{
    int heso;
    int somu;
    dt *Next;
} dathuc;
dathuc *ptam, *C;
dathuc *in(dathuc *P,dathuc *pdau,char S)
{
    int heso;
    int somu;
    printf("Nhap da thuc %c",S);
    do
    {
        printf("\nNhap so mu: ");
        scanf("%d",&somu);
        if(somu == 13)
            break;
        if(pdau==NULL)
        {
            P=(dathuc *) malloc(sizeof(dathuc));
            pdau=P;
        }
        else
        {
            P->Next=(dathuc *) malloc(sizeof(dathuc));
            P=P->Next;
        }
        P->somu = somu;
        printf("Nhap he so: ");
        scanf("%d",&heso);
        P->heso=heso;
        P->Next=NULL;
    }
    while (getch() != 0x1b);
    return pdau;
}
void out(dathuc *p,dathuc *pdau,char S)
{
    p=pdau;
    printf("\n%c = ",S);
    do
    {
        if(p==pdau)
        {
                printf("%dx^%d",p->heso,p->somu);

        }
        else{
            if(p->heso <0 )
                printf("%d^%d",p->heso,p->somu);
            else
                printf("+%d^%d",p->heso,p->somu);
        }

            p=p->Next;
    }
    while(p!=NULL);
}
void attach(int H,int M)
{
    dathuc *a;
    a = (dathuc*)malloc(sizeof(dathuc));
    a->heso = H;
    a->somu = M;
    if(C!=NULL){
        ptam->Next = a;
    }
    else
        C = a;
    ptam =a;

}
void add(dathuc *P,dathuc *pP,dathuc *Q,dathuc *pQ,dathuc *C)
{
    P = pP;
    Q = pQ;
    while(P!=NULL && Q!=NULL)
    {

        if(P->somu == Q->somu)
        {
            int A  = P->heso + Q->heso;
            attach(A,P->somu);
            P = P->Next;
            Q = Q->Next;
        }
        else{
            if(P->somu > Q->somu){
                attach(P->heso,P->somu);
                P = P->Next;
            }
            else{
                attach(Q->heso,Q->somu);
                Q = Q->Next;
            }
        }
    }
}
main()
{
    int a,n;
    dathuc *P,*pdau_p,*Q,*pdau_q;
    pdau_p = in(P,NULL,'P');
    pdau_q = in(Q,NULL,'Q');
    out(P,pdau_p,'P');
    out(P,pdau_q,'Q');
    add(P,pdau_p,Q,pdau_q,C);
    //out(C,C,'C');
}