swap pair in a linked list

swappair.c

#include <stdio.h>
#include <stdlib.h>
struct tnode
{
int data;
struct tnode *link;
};
typedef struct tnode *tptr;
tptr insert(tptr first,int x)
{
   tptr p,t;
   p=(tptr)malloc(sizeof(struct tnode));
   p->data=x;
   p->link=NULL;
   if(first==NULL)
   {
   first=p;
   return first;
   }
   t=first;
   while(t->link!=NULL)
   t=t->link;
   t->link=p;
   return first;

}
void display(tptr first)
{
   tptr t;
   t=first;
    while(t!=NULL)
    {
      printf("%d ",t->data);
      t=t->link;
    }
}
void swap(tptr t1,tptr t2)
{
   int temp;
   temp=t1->data;
   t1->data=t2->data;
   t2->data=temp;
}
void pairswap(tptr first)
{
   tptr next,temp,t1,t2;
   temp=first;
   while(temp!=NULL)
   {
      t1=temp;
      if(temp->link==NULL)
      break;
      t2=temp->link;
      next=t2->link;
      swap(t1,t2);
      temp=next;
   }
}
int main()
{
  int x;
  tptr first;
  first=NULL;

  scanf("%d",&x);
  while(x!=-1)
  {
    first=insert(first,x);
    scanf("%d",&x);
  }
  pairswap(first);
  display(first);
  return 0;
}