请帮忙看下以下程序错没错，谢谢
srtuct stu
{
    int no;
    struct stu *next;
};
struct stu *insert(struct stu *ah,struct stu *bh)//ah和bh两个链表合并，按学号升序排列
{
    struct stu *pa1,*pa2,*pb1,*pb2;
    pa1=pa2=ah;
    pb1=pb2=bh;
    do
    {
        while((pb1->no>pa1->no)&&(pa1->next!=null))
        {
            pa2=pa1;
            pa1=pa1->next;
        }
        if(pb1->no<=pa1->no)
        {
            if(ah==pa1)
                ah=pb1;
            else
                pa2->next=pb1;
            pb1=pb1->next;
            pb2->next=pa1;
            pa2=pb2;
            pb2=pb1;
        }
    }while((pa1->next!=null)||(pa1==null&&pb1!=null));
    if((pb1!=null)&&(pb1->no>pa1->no)&&(pa1->next==null))
        pa1->next=pb1;
    return (ah);
}