Getting Segmentation fault error

Question

I was trying to add to polynomials by using linked lists but couldn't understand the reason of segmentation fault at this line <printf("%d",p->coe);>
I understand that this error is shown when we try to access an illegal memory location but in this case i am not able to understand the cause.
Please Help.

Program below:

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

struct node {
int coe;
int deg;
struct node *next;
};

typedef struct node Node;

Node *newnode() {
Node *p = (Node*)malloc((sizeof(Node)));
p->next = NULL;
return p;
}

Node *head1 = NULL,*head2 = NULL,*head3 = NULL;

void create(Node **p,int coeff,int degree) {
Node *temp = newnode();
temp->coe = coeff;
temp->deg = degree;
Node *q;
if(*p==NULL) {
*p = temp;
} else {
q = *p;
while(q->next!=NULL) {
q = q->next;
}
q->next = temp;
temp->next = NULL;
}
}

void display(Node **p) {
while(*p!=NULL) {
printf("%dx^%d+",(*p)->coe,(*p)->deg);
*p = (*p)->next;
}
}

int main() {
int coeff,degree;
printf("Enter first polynomial in the format <coefficient> <degree>:");
scanf("%d %d",&coeff,&degree);
create(&head1,coeff,degree);
while(degree>0) {
degree--;
printf("\nEnter coeff. for x^%d:",degree);
scanf("%d",&coeff);
create(&head1,coeff,degree);
}
printf("\nEnter second polynomial in the format <coefficient> <degree>:");
scanf("%d %d",&coeff,&degree);
create(&head2,coeff,degree);
while(degree>0) {
degree--;
printf("\nEnter coeff. for x^%d:",degree);
scanf("%d",&coeff);
create(&head2,coeff,degree);
}
display(&head1);
display(&head2);
printf("-------------\n");
Node *p = head1,*q = head2;
/*while(p->next!=NULL) {
if(p->deg == q->deg) {
create(&head3,p->coe+q->coe,p->deg);
}
else if(p->deg>q->deg) {
create(&head3,p->coe,p->deg);
create(&head3,q->coe,q->deg);
}
else {
create(&head3,q->coe,q->deg);
create(&head3,p->coe,p->deg);
}
p = p->next;
q = q->next;
}

Answer 1

why not put it in code playground and link it here, it will be easy to debug that way, looks rough to me now

Answer 2

Agreed with ✳AsterisK✳ ! Would be glad to help but it is hard this way :)

Answer 3

Oh, I shouldn't have spoken too quickly. I think the error is because display modify the value of head1 so p is NULL
Use a simple pointer for this one instead of a double and it should work (at least for this error ^^)

Answer 4

✳AsterisK✳ is right.

Segmentation fault error, what a classic :)

Answer 5

Yeah I got it! Thanks for the help!
And please forgive me for not putting the code in playground.I'll take care of this the next time.

Answer 6

display(&head3);*/
printf("%d",p->coe);
getch();
return 0;
}
<This portion got omitted from the question,so i'm writing it here.>