pta 5-2 多项式乘法与加法，段错误什么原因？

Question

 #include<stdio.h>
#include<stdlib.h>
typedef struct _polynomial* Polynomial;
typedef struct _polynomial* Item;
struct _polynomial{
    int e;
    int x;
    Item next;
};
Item NewItem(int e,int x);
Polynomial Read_Poly();
void Print_Poly(Polynomial p);
Polynomial Add_Poly(Polynomial p1,Polynomial p2);
Polynomial Multi_Poly(Polynomial p1,Polynomial p2);

int main(){
    Polynomial p1,p2;
    p1 = Read_Poly();
    p2 = Read_Poly();
    Print_Poly( Multi_Poly( p1,p2 ));
    Print_Poly( Add_Poly(p1,p2));
    free(p1); free(p2);
    return 0;
}
Polynomial Read_Poly(){
    int t;
    int x,e;
    Polynomial p,pnew,phead;
    phead = (Polynomial) malloc(sizeof(struct _polynomial));
    p = phead;


    scanf("%d",&t);
    if( t == 0) return NULL;
    while( t--){
        scanf("%d %d",&x,&e);
        pnew = (Polynomial ) malloc(sizeof(struct _polynomial));
        pnew->e = e;
        pnew->x = x;
        pnew->next = NULL;
        p->next = pnew;
        p = pnew;
    }
    p = phead;
    phead = phead->next;
    free(p);
    return phead;
}
void Print_Poly(Polynomial p) {
    Item i = p;
    int tag = 1;
    if( p == NULL) {   
        printf("0 0\n");
        return ;
    }
    while( i){
        if( tag == 0) putchar(' ');  
        else tag=0;
        printf("%d %d",i->x,i->e);
        i = i->next;
    }
    putchar('\n');
}
Polynomial Add_Poly(Polynomial p1,Polynomial p2){
    Polynomial res;
    Item i1,i2,pnew,p;


    i1 = p1; i2 = p2;
    res = (Polynomial) malloc( sizeof( struct _polynomial));
    res->next = NULL;
    p = res;
    while( i1 && i2){
        if( i2->e > i1->e) {  
            pnew = NewItem(i2->e,i2->x);
            p->next = pnew;
            p = pnew;

            i2=i2->next;
        }
        else if( i1->e > i2->e) { 
            pnew = NewItem(i1->e,i1->x);
            p->next = pnew;
            p = pnew;
            i1=i1->next;

        }
        else {

            if( i1->x + i2->x != 0){
                pnew = NewItem(i2->e,i1->x + i2->x );
                p->next = pnew;
                p = pnew;
            }
            i1 = i1->next; i2 = i2->next;


        }
    }
    while( i1) {

        pnew = NewItem(i1->e,i1->x);
        p->next = pnew;
        p = pnew;
        i1=i1->next;
    }
    while( i2){

        pnew  = NewItem(i2->e,i2->x);
        p->next = pnew;
        p = pnew;
        i2 = i2->next;
    }

    pnew = res;
    res = res->next;
    free(pnew);
    return res;
}
Item NewItem(int e,int x){
    Item i = (Item) malloc(sizeof(struct _polynomial));
    i -> e = e;
    i -> x = x;
}
Polynomial Multi_Poly(Polynomial p1, Polynomial p2){
    Item i1,i2;
    Polynomial res,p,pr,pnew;
    res  = NULL;
    i1 = p1;
    while( i1 ){
        pr = (Polynomial) malloc( sizeof( struct _polynomial));
        p = pr;
        i2 = p2;
        while( i2) {
            pnew = NewItem(i1->e+i2->e, i1->x * i2->x);
            p->next =  pnew;
            p = pnew;

            i2 = i2->next;
        }
        p = pr; pr = pr->next; free(p);
        res  =  Add_Poly(res,pr);
        free(pr);


        i1 = i1->next;
    }
    return res;
}

Answer 1

http://blog.csdn.net/bbbbswbq/article/details/68482726