简单的链表为什么插入1 时候有异常 ，别的时候正常

简单的链表为什么插入1 时候有错误 ，别的时候正常


代码谢谢指导啊
#include <iostream>
#include <cstdlib>
#include <ctime>
#include <cmath>
using namespace std;
struct node {
int a;
node*next;
};
void sort1(node * head1,node *end1)
{
    for(node*i=head1;i!=end1;i=i->next)
    {

        for(node*j=i->next;j!=NULL;j=j->next)
        {
            if(j->a>i->a)
            {
                int temp_swap=j->a;
                j->a=i->a;
                i->a=temp_swap;
            }
        }
    }

}
void insert1(node*& head1,node* &end1)
{
     cout<<"input the data to insert :";
    node* insert_node=new node;
    cin>>insert_node->a;
    insert_node->next=NULL;

    node *cur=head1;node*pre=head1;
    if((insert_node->a)>=(head1->a))
    {
        insert_node->next=head1;
        head1=insert_node;
    }
    else
{                                               
    while(((insert_node->a)<(cur->a))&&(cur!=NULL))//估计这有问题
    {   pre=cur;
        cur=cur->next;
        cout<<"try";
    }
    if(cur==NULL)
    {
        pre->next=insert_node;
        pre->next->next=NULL;
        end1=pre->next;
    }
    else                                           //估计到这有问题
    {
        insert_node->next=pre->next;
        pre->next=insert_node;
        cout<<"hahahahaha"<<endl;
    }
}
}
void show_list(node*head1,node*end1)
{
  node *temp=head1;
  while(temp!=NULL)
  {
      cout<<temp->a<<" ";
      temp=temp->next;

  }
  cout<<endl;
}
int main()
{
    srand(time(NULL));
    cout<<"input the size  "<<endl;
    int size;
    cin>>size;
    node *head=NULL;node *current=NULL;
    for(int i=0;i<size;i++)
    {
        node *temp=new node;
        cout<<"input the data :";
        //cin>>temp->a;
        temp->a=rand();
        if(head==NULL)
        {
            head=temp;
          current=temp;
        }
        else
        {
            current->next=temp;
            current=current->next;
        }

    }
    current->next=NULL;
    cout<<"before sort "<<endl;
    show_list(head,current);
    cout<<"sort the list"<<endl;
    sort1(head,current);
    show_list(head,current);

    insert1(head,current);
    show_list(head,current);

    cout << "Hello world!" << endl;
    return 0;
}
[解决办法]
while(((insert_node->a)<(cur->a))&&(cur!=NULL))//估计这有问题
改为
while((cur!=NULL) && ((insert_node->a)<(cur->a)))
要先保证cur!=NULL后才能引用cur->a。