Representing Polynomials using Linked List

Here's a simple application of a singly linked list. It can be used to represent polynomials and we can add and subtract two polynomials with the help of it.

	#include <stdio.h>
	#include <stdlib.h>
	struct node{
	int c,e;
	struct node *next;
	};
	struct node *create(struct node *p);
	struct node *insert(struct node *root, int c, int e);
	struct node *add_poly(struct node *p1, struct node *p2, struct node *root);
	struct node *sub_poly(struct node *p1, struct node *p2, struct node *root);
	void display(struct node *p);
	int main()
	{
	struct node *p1 = NULL, *p2 = NULL, *p3 = NULL, *p4 = NULL;
	printf("1st polynomial:\n");
	p1 = create(p1);
	printf("2nd polynomial:\n");
	p2 = create(p2);
	printf("First polynomial looks like:\n");
	display(p1);
	printf("Second polynomial looks like:\n");
	display(p2);
	p3 = add_poly(p1, p2, p3);
	printf("Result of addition:\n");
	display(p3);
	p4 = sub_poly(p1, p2, p4);
	printf("Result of subtraction:\n");
	display(p4);
	return 0;
	}
	struct node *create(struct node *p){
	struct node *nn, *last = NULL;
	int coeff,exp;
	printf("Enter coeff and exp or enter -1 to stop: ");
	scanf("%d%d", &coeff,&exp);
	while(coeff != -1 || exp != -1){
	nn = (struct node *)malloc(sizeof(struct node));
	nn->c = coeff;
	nn->e = exp;
	nn->next = NULL;
	if(p == NULL){
	p = nn;
	last = nn;
	}else{
	last->next = nn;
	last = nn;
	}
	printf("Enter coeff and exp or enter -1 to stop: ");
	scanf("%d%d", &coeff,&exp);
	}
	return p;
	};
	void display(struct node *p){
	while(p != NULL){
	if(p -> e != 0) {
	printf("%dx^%d ", p->c, p->e);
	} else {
	printf("%d", p -> c);
	}
	p = p->next;
	}
	printf("\n");
	}
	struct node *add_poly(struct node *p1, struct node *p2, struct node *root){
	// Adds p1 and p2 and stores result in root tree
	while(p1!= NULL && p2 != NULL){
	if(p1->e == p2->e){
	root = insert(root, p1->c + p2->c, p1->e);
	p1 = p1->next;
	p2 =
	p2->next;
	}
	else if(p1->e > p2->e){
	root = insert(root, p1->c,p1->e);
	p1 = p1->next;
	}
	else{
	root = insert(root,p2->c, p2->e);
	p2 = p2->next;
	}
	}
	while(p1 != NULL){
	root = insert(root,p1->c, p1->e);
	p1 = p1->next;
	}
	while(p2 != NULL){
	root = insert(root,p2->c, p2->e);
	p2 = p2->next;
	}
	return root;
	}
	struct node *sub_poly(struct node *p1, struct node *p2, struct node *root){
	//Subtracts p1 and p2 and stores result in root tree
	while(p1 != NULL && p2 != NULL) {
	if(p1 -> e == p2 -> e) {
	root = insert(root, p1 -> c - p2 -> c, p1 -> e);
	p1 = p1 -> next;
	p2 = p2 -> next;
	} else if(p1 -> e > p2 -> e) {
	root = insert(root, p1 -> c, p1 -> e);
	p1 = p1 -> next;
	} else {
	root = insert(root, -p2 -> c, p2 -> e);
	p2 = p2 -> next;
	}
	}
	while(p1 != NULL) {
	root = insert(root, p1 -> c, p1 -> e);
	p1 = p1 -> next;
	}
	while(p2 != NULL) {
	root = insert(root, -p2 -> c, p2 -> e);
	p2 = p2 -> next;
	}
	return root;
	}
	struct node *insert(struct node *root, int c, int e){
	//Inserts a node in tree of root
	struct node *nn, *p;
	nn = (struct node *)malloc(sizeof(struct node));
	nn->c = c;
	nn->e = e;
	nn->next = NULL;
	if(root == NULL){
	root = nn;
	}else{
	p = root;
	while(p -> next != NULL) {
	p = p -> next;
	}
	p -> next = nn;
	}
	return root;
	}