Adding and Subtracting Polynomials Using Linked Lists

#include <stdio.h>
#include <stdlib.h>
struct node{
    int exponent;
    int coefficient;
    struct node* next;
};
struct node* create(int e, int c){
    struct node *newNode = (struct node*) malloc(sizeof(struct node));
    newNode->exponent = e; newNode->coefficient = c; newNode->next = NULL;
    return newNode;
}
struct node* insert(struct node *head, struct node *newNode){
    if(!head || newNode->exponent > head->exponent){
        newNode->next = head;
        head = newNode;
    }
    else{
        struct node *help = head, *prev = NULL;
        while(help && newNode->exponent < help->exponent){
            prev = help;
            help = help->next;
        }
        if(help && newNode->exponent == help->exponent) help->coefficient+=newNode->coefficient;
        else{
            newNode->next = help;
            prev->next = newNode;
        }
    }
    return head;
}
void display(struct node* head){
    struct node *help = head;
    while(help){
        printf("%d", help->coefficient);
        printf("X^(%d)+", help->exponent);
        help = help->next;
    }
    printf("0");
}
struct node* enter(struct node *head, int n){
    int i, e, c;
    for(i = 0; i < n; i++){
        printf("\n\nEnter the exponent: ");
        scanf("%d", &e);
        printf("Enter the coefficient: ");
        scanf("%d", &c);
        head = insert(head, create(e,c));
    }
    return head;
}
struct node *copy(struct node* headC, struct node* headA){
    struct node *last = NULL;
    while(headA){
        struct node* newNode = create(headA->exponent, headA->coefficient);
        if(!headC) headC = last = newNode;
        else{
            last->next = newNode;
            last = newNode;
        }
        headA = headA->next;
    }
    return headC;
}
void add(struct node *headA, struct node *headB){
    struct node *headC = NULL;
    headC = copy(headC, headA);
    struct node *helpB = headB;
    while(helpB){
        headC = insert(headC, create(helpB->exponent, helpB->coefficient));
        helpB = helpB->next;
    }
    printf("\n\nThe addition of polinomials A and B is ");
    display(headC);
}
void sub(struct node *headA, struct node *headB){
    struct node *headC = NULL;
    headC = copy(headC, headA);
    struct node *helpB = headB;
    while(helpB){
        headC = insert(headC, create(helpB->exponent, -helpB->coefficient));
        helpB = helpB->next;
    }
    printf("\nThe subtraction of polinomials A and B is ");
    display(headC);
}
int main(){
    int nA, nB;
    struct node *headA = NULL;
    struct node *headB = NULL;
    printf("Enter the number of terms for A: ");
    scanf("%d", &nA);
    headA = enter(headA, nA);
    printf("\nEnter the number of terms for B: ");
    scanf("%d", &nB);
    headB = enter(headB, nB);
    printf("\n\nPolynomial A is :- ");
    display(headA);
    printf("\nPolynomial B is :- ");
    display(headB);
    add(headA, headB);
    sub(headA, headB);
}