Polynomial Addition

The following is a C program to implement polynomial addition. If you have any doubts please let me know.
#include<stdio.h>
#include<stdlib.h>
struct node
{
 int d;
 int coef;
 struct node *next;
}*newn,*n=NULL,*p=NULL,*q=NULL,*r=NULL,*start1=NULL,*start2=NULL,*start3=NULL,*ptr=NULL,*prev=NULL;
void display(struct node *,struct node *);
void display1();
main()
{
 int a,b,i;
 i=0;
 printf("\nEnter values for polynomial1:\n");
 do
  {
 printf("Enter the coeff of x^%d:",i);
      newn=(struct node *)malloc(sizeof(struct node));
      scanf("%d",&newn->coef);
      newn->d=i;
      newn->next=p;
      p=newn;
      i++;
 printf("\n Do you wish to add more elements in polynomial 1:");
      printf("\nPress 1 to continue");
    scanf("%d",&a);
  }while(a==1);
 start1=p;
 printf("POLYNOMIAL 1:");
 display(start1,p);
 i=0;
 printf("\n\nEnter values for polynomial2:\n");
 do
 {
  printf("Enter the coef of x^%d:",i);
  newn=(struct node *)malloc(sizeof(struct node));
  scanf("%d",&newn->coef);
  newn->d=i;
  newn->next=q;
  q=newn;
  i++;
  printf("\n Do you wish to add more elements in polynomial 2:");
  printf("\nPress 1 to continue");
  scanf("%d",&b);
 }while(b==1);
 start2=q;
 printf("POLYNOMIAL 2:");
 display(start2,q);
 printf("\n\nSUM:");
 p=start1;
 q=start2;
 while((p!=NULL)&&(q!=NULL))
 {
if(p->d==q->d)
{
newn=(struct node *)malloc(sizeof(struct node));
newn->next=r;
newn->coef=p->coef+q->coef;
newn->d=p->d;
p=p->next;
q=q->next;
r=newn;
}
else if(p->d>q->d)
{
newn=(struct node *)malloc(sizeof(struct node));
newn->next=r;
newn->coef=p->coef;
newn->d=p->d;
p=p->next;
r=newn;
}
else if(p->d<q->d)
{
newn=(struct node *)malloc(sizeof(struct node));
newn->next=r;
newn->coef=q->coef;
newn->d=q->d;
q=q->next;
r=newn;
}
 }
 if(p==NULL)
 {
while(q!=NULL)
{
newn=(struct node *)malloc(sizeof(struct node));
newn->next=r;
newn->coef=q->coef;
newn->d=q->d;
q=q->next;
r=newn;
}
 }
 else if(q==NULL)
 {
while(p!=NULL)
{
newn=(struct node *)malloc(sizeof(struct node));
newn->next=r;
newn->coef=p->coef;
newn->d=p->d;
p=p->next;
r=newn;
}
 }

 start3=r;
 display1();
}

void display(struct node *start,struct node *ptr)
{
 ptr=start;
 while(ptr!=NULL)
 {
   printf("%dx^%d",ptr->coef,ptr->d);
   if(ptr->next!=NULL)
  printf("+");
   ptr=ptr->next;
 }
}
void display1()
{
 r=start3;
 prev=NULL;
 while(r!=NULL)
 {
   ptr=prev;
   prev=r;
   r=r->next;
   prev->next=ptr;
 }
 start3=prev;
 r=start3;
 while(r!=NULL)
 {
   printf("%dx^%d",r->coef,r->d);
   if(r->next!=NULL)
  printf("+");
   r=r->next;
 }
}