A question about the polynomial---impelemented with list

[rpbear]

Hi all.I wrote a program to impelement the add operation of polynomial with list.For example,I wanna do the add operation on
x^2+3x^4+6x^5 AND x-5x^4+x^5-4x^6
I creat two list,the input should be:
1 2
3 4
6 5
EOF
1 1
-5 4
1 5
-4 6
EOF
my question is at Line 137~140.I haven't initialize the local variable P,however,It has a value!Why?I think it's the key to fix my program.

#include<stdio.h>
#include<malloc.h>

typedef struct Polynomial{
    int coe;
    int order;
    struct Polynomial *next;
}Poly;

int creat_list(Poly** head);
void print_list(Poly *head);
void insert_node(Poly *head,Poly *py);
void del_node(Poly *head,Poly *py);
void add_poly(Poly *h1,Poly *h2);
void print_result(Poly *head);

int main(){

    Poly *head1,*head2;
    creat_list(&head1);
//printf("---------------------\n");
//    print_list(head1);
    creat_list(&head2);
//printf("---------------------\n");
//    print_list(head2);
    add_poly(head1,head2);
printf("---------------------\n");
    print_result(head1);
    return 0;
}

int creat_list(Poly** head){
    int coe,order;
    *head = (Poly*)malloc(sizeof(Poly));
    if(*head == NULL) return 0;

    Poly *p = *head;
    (*head)->next = NULL;
    printf("input the coe and order:\n");
    while(scanf("%d %d",&coe,&order) == 2){
//The algorithm will be right only if
//you enter the unique order in order.
        Poly *newnode = (Poly *)malloc(sizeof(Poly));
        newnode->coe = coe;
        newnode->order = order;
        newnode->next = NULL;
        p->next = newnode;
        p = newnode;
        printf("input the coe and order:\n");
    }
    return 1;
}

void insert_node(Poly *head,Poly *py){
    int flag = 0;
    Poly *pre = head->next,*aft = head;
    while(pre){
        if(pre->order < py->order){
            aft = pre;
            pre = pre->next;
            continue;
        }
        else if(pre->order > py->order){
            aft->next = py;
            py->next = pre;
            flag = 1;
            break;
        }
        else{
            if(pre->coe+py->coe){
                pre->coe += py->coe;
                flag = 1;
                break;
            }
            else{
                Poly p = *py;
                del_node(head,&p);
                flag = 1;
                break;
            }
        }
    }
    if(!flag){
        aft->next = py;
        py->next = NULL;
    }
}

void del_node(Poly *head,Poly *py){

    Poly *pre = head->next,*aft = head;
    while(pre){
        if(pre->coe == py->coe &&\
            pre->order == py->order){
            aft->next = pre->next;
            //break;
            //ignore break in case of more than one matched
        }
        aft = pre;
        pre = pre->next;
    }

}

void add_poly(Poly *h1,Poly *h2){
    Poly *pre = h1->next,*aft = h1;
    Poly *p2 = h2->next;

    while(p2 && pre){
        if(pre->order < p2->order){
            aft = pre;pre = pre->next;
            continue;
        }
        else if(pre->order > p2->order){
            Poly p = *p2;

            insert_node(h1,&p);
            p2 = p2->next;
            continue;
        }
        else{
            if((pre->coe+p2->coe) == 0){
                aft = pre;pre = pre->next;
                del_node(h1,aft);
                p2 = p2->next;
            }
            else{
                pre->coe += p2->coe;
                aft = pre;pre = pre->next;
                p2 = p2->next;
            }
        }
    }

    if(pre == NULL){
        while(p2){
print_list(h1);
            Poly p;//p = *p2;
            printf("&&%d %d\n",p.coe,p.order);
print_list(h1);
            insert_node(h1,&p);
            p2 = p2->next;
        }
    }
}

void print_result(Poly *head){
    Poly *p = head->next;
    while(p){
        printf("%+dx^%d",p->coe,p->order);
        p = p->next;
    }
    printf("\n");
}

void print_list(Poly *head){
    Poly *p = head->next;
    while(p != NULL){
        printf("%d %d\n",p->coe,p->order);
        p = p->next;
    }
}

[Memloop]

> I haven't initialize the local variable P,however,It has a value!Why?

Well it has to have some value. Since you haven't initialized it with a value, the initial value is going to be whatever value that is at the memory location that the variable is bound to.

[rpbear]

> I haven't initialize the local variable P,however,It has a value!Why?

Well it has to have some value. Since you haven't initialized it with a value, the initial value is going to be whatever value that is at the memory location that the variable is bound to.

I understand.However,if I change the p's value,the value of the list will change,I don't know why