C++一元多项式相加的结果输出有关问题

C++一元多项式相加的结果输出问题
输出多项式系数出问题，输出不全，但是只输出指数就没问题；
问题行已经标记了：
 cout<<p->data.coef<<" "<<p->data.expn<<" "<<endl;//就是这里的p->data.coef出问题了

代码如下：


#include <iostream>
using namespace std;

struct term
{
  double coef;//系数
  int expn;//指数
  };

struct PNode
{
  term data;
  PNode *next;
  };

class Polyn
{
  public:
  Polyn(){phead = new PNode;phead->next=NULL;}
  ~Polyn(){
  do{delete phead;
  phead=phead->next;
  }while(phead!=NULL);
  }
  void clear(){phead->next=NULL;}
  void creatp();
  Polyn PolyAdd(Polyn Pb);
  void Print();
  private:
  PNode *phead;
  };
   
Polyn Polyn::PolyAdd(Polyn Pb)  
{
  Polyn Pc;
  PNode *p1,*p2,*p3;
  p1=phead;
  p2=Pb.phead;
  p3=Pc.phead; 
  PNode *t1=p1->next,*t2=p2->next,*t3=p3;
  while(t1&&t2)
  {
  if(t1->data.expn<t2->data.expn)
  {
  t3->next=new PNode;
  t3=t3->next;
  t3->data=t1->data;
  t1=t1->next;
  cout<<1<<endl;
  }
  else if(t1->data.expn>t2->data.expn)
  {
  t3->next=new PNode;
  t3=t3->next;
  t3->data=t2->data;
  t2=t2->next;
  cout<<2<<endl;
  }  
  else{
  double a=t1->data.coef+t2->data.coef;
  if(a!=0.0)
  {
  t3->next=new PNode;
  t3=t3->next;
  t3->data.coef=a;
  t3->data.expn = t1->data.expn;
  }
  t1=t1->next;
  t2=t2->next; 
  cout<<3<<endl;
  }
  }
  while(t1!=NULL){
  t3->next=new PNode;
  t3=t3->next;
  t3->data=t1->data;
  t1=t1->next;
  }
  while(t2!=NULL){
  t3->next=new PNode;
  t3=t3->next;
  t3->data=t2->data;
  t2=t2->next;
  }
  t3->next=NULL;
  return Pc;
  }
void Polyn::creatp()
 {
  PNode *p,*q;
  int n;
  q=phead;
  cout<<"输入n"<<endl;
  cin>>n;
  cout<<"输入各项系数和指数："<<endl;