显示的系数总是为0，多项式和为zero item。我是新手，虚心求教

#include <stdio.h>
#include <stdlib.h>
typedef struct polynomials
{
    int coef;
    int exp;
    struct polynomials *next;
}poly;

poly *create(){
    int n;
    poly *head;
    poly *p1,*p2;
    n=0;
    p1=p2=(poly*)malloc(sizeof(poly));
    scanf("%d%d",&p1->coef,&p1->exp);
    if(p1->next==0)head=NULL;
    else
    {
        while(p1->coef!=0)
        {n++;
        if(n==1)head=p1;
        else p2->next=p1;
        p2=p1;
        scanf("%d%d",&p1->coef,&p1->exp);
        }
        p2->next=NULL;
    }
    return head;
}

void print(poly *p){
    poly *q;
    q=p;
    printf(" ");
    if(q!=0)
        do
        {
           printf("%dX^%d",q->coef,q->exp);
                q=q->next;
            if(q!=0)printf("+");
        }while(q!=0);
        else printf("zero item");
        printf("\n");
}
int compare(poly *a,poly *b){
if(a->exp>b->exp)return 1;
else if(a->exp<b->exp)return -1;
return 0;
}
poly *add(poly *a,poly *b){
    poly *head,*polya=a,*polyb=b,*p,*q;
    int sum;
    head=p=(poly*)malloc(sizeof(poly));
    p->next=NULL;
    while(polya&&polyb){
        switch(compare(polya,polyb)){
        case -1:
            p->next=polyb;
            p=polyb;
            polyb=polyb->next;
            break;
        case 0:
            sum=polya->coef+polyb->coef;
            if(sum!=0){
                polya->coef=sum;
                p->next=polya;
                p=polya;
                polya=polya->next;
            }
            else{
                q=polya;
                polya=polya->next;
                free(q);
            }
            q=polyb;
            polyb=polyb->next;
            free(q);
            break;
        case 1:
            p=polya->next;
            p=polya;
            polya=polya->next;
            break;
            }
        }
        if(polya)p->next=polya;
        if(polyb)p->next=polyb;
        q=head;
        head=head->next;
        free(q);
        return head;
}

int main(){
    poly *a,*b,*s;
    printf("input polynomials a: ");
    a=create();
    printf("input polynomials b: ");
    b=create();
    printf("poly_a:\n");
    print(a);
    printf("poly_b:\n");
    print(b);
    printf("poly_sum:\n");
    s=add(a,b);
    print(s);
}

[ 本帖最后由 ste11ar 于 2009-9-26 13:26 编辑 ]

先测试你的creat（），这个只要建完表打印输出就知道了
再测试add（），在函数结束之前测试加法操作之后的sum是否建表成功（很可能就是这里的问题）
多写几个printf()就容易测出来了。