//创建的是一个以学生学号和成绩作为数据的链表。在此处只设立两个节点。struct Student{ long num; float score; struct Student *next;}*p1,*p2;struct Student *creat(){ struct Student *head; int n=0; scanf("%ld,%f",&p1->num,&p1->score); head=0; while(p1->num!=0) {  n=n+1;  if(n==1)   head=p1;  else   p2->next=p1;  p1=p2;  scanf("%ld,%f",&p1->num,&p1->score); } p2->next=0; return(head);}问题是：\Program Files\Microsoft Visual Studio\MyProjects\zxc\123.cpp(12) : error C2065: 'scanf' : undeclared identifier