写了一个简单的动态链表，但是在执行的时候虽然提示输入第二个多项式，但实际上相当于无效输入，根本不显示多项式二的数据，如图：

#include <stdio.h>
#include <stdlib.h>
typedef struct ploy {
    double coef;
    int expn;
    struct ploy *next;
}Linklist;
int n = 0;

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

void visit(Linklist *temp)
{
    Linklist *ploy;
    int i = 0;
    ploy = temp;
    while (ploy)
    {
        if (i == 0)
        {
            printf("%3.2lf*X^%d", ploy->coef, ploy->expn);
            ploy = ploy->next;
            i = 1;
        }
        else if (ploy->coef<0)
        {
            printf("%3.2lf*X^%d", ploy->coef, ploy->expn);
            ploy = ploy->next;
        }
        else if (ploy->coef>0)
        {
            printf("+%3.2lf*X^%d", ploy->coef, ploy->expn);
            ploy = ploy->next;
        }
    }
}

Linklist *sum(Linklist *ploy1, Linklist *ploy2)
{
    Linklist *ptr1, *ptr2, *temp, *head;
    temp = (Linklist *)malloc(sizeof(Linklist *));
    head = ptr1 = ploy1;
    ptr2 = ploy2;
    while (ptr1 != NULL&&ptr2 !=NULL)
    {
        if (ptr1->expn == ptr2->expn)
        {
            ptr1->coef = ptr1->coef + ptr2->coef;
            ptr1 = ptr1->next;
            ptr2 = ptr2->next; 
        }
        else if (ptr1->expn < ptr2->expn)
        {
            ptr1 = ptr1->next;
        }
        else if (ptr1->expn > ptr2->expn)
        {
            temp->coef = ptr2->coef;
            temp->expn = ptr2->expn;
            temp->next = ptr1->next;
            ptr1->next = temp;
            ptr2 = ptr2->next;
        }
    }
    return head;
}
int main()
{
    Linklist *L, *H, *result;
    printf("输入多项式一：\n");
    L = creat();
    printf("输入多项式二：\n");
    H = creat();
    printf("输入的数据为：\n");
    visit(L); visit(H);
    result = sum (L, H);
    printf("结果：\n");
    visit(result);
    printf("\n");
    return 0;
}

int n = 0;这个你设置成全局变量干啥？？？
第一个多项式head指向链表头，第二个多项式，由于n是一个很大的值了，if(n==1)不可能成立，head为空，所以第二个多项式不会显示

int n=0;应该放在下面函数里面，局部变量
Linklist *creat()
{

嗯嗯，总算懂明白了