一元多项式加法函数的程序不知错哪里啦

这段程序编译时能通过，就是不能实现，运行时，直接跳过，求改错！


void add(){
   
 lnode *s1,*s2,*temp;
 lnode *pre=NULL;
 float sum;
 s1=H1;
 s2=H2;
 pre=new lnode;
 pre->next=H1;
 
 while(s1!=NULL&&s2!=NULL){
 if(s1->b<s2->b){
     pre->next=s1;
     pre=pre->next;
     s1=s1->next;
   
 
 }
 
 else if(s1->b==s2->b){
     sum=s1->a+s2->a;
     if(sum==0){
         temp=s1;
         s1=s1->next;
         delete temp;
         temp=s2;
         s2=s2->next;
         delete temp;
     }
     else {
         s1->a=sum;
        
         pre->next=s1;
         pre=pre->next;
         s1=s1->next;
         temp=s2;
         s2=s2->next;
         delete temp;
         

          }
     
 }     
 else{
     pre->next=s2;
     pre=pre->next;
     s2=s2->next;
     
 }
 }

 if(s1!=NULL)
     pre->next=s1;
   
 
 else
     pre->next=s2;
     
 

     cout<<"相加后的结果为:"<<endl;
      s1=H1;   
 while(s1){
   


         if(s1!=H1&&s1->a>0)
            
             cout<<"+"<<s1->a<<"x^"<<s1->b;
            
         
         else
             cout<<s1->a<<"x^"<<s1->b;
        
     s1=s1->next;
 }
 cout<<endl;
 
  }