C语言链表的实验有问题

该段代码调试了N次，还是存在问题，不知道该怎么改了。

/*编写一个建立考生链表的函数 creat() .每个考生的数据包括准考证号 (8字符)   姓名(16字符)  总分三个部分*/ #include <stdio.h> #include <string.h> #include <stdlib.h> #define NULL 0 struct student { char Num[9]; char Name[16]; int score ; struct student *next; }; struct student  *creat(  ) { struct student *head , *tail , *New ; char Num[9]; char Name[16]; int score; int size = sizeof ( struct student ); head = tail = NULL ; printf ( "please input the first DATA : /n  Number  Name Score /n"); scanf ( " %s ", Num ); scanf ( " %s ", Name ); scanf ( " %d ", &score ); while ( score != 0 ) { New = ( struct student *)malloc ( size );  // 为新结点开辟内存空间 strcpy ( New -> Num , Num ); strcpy ( New -> Name, Name );     New -> score = score ; New -> next = NULL ; if ( head == NULL ) head =New ; else tail -> next = New ; tail =New; printf ( "Please input the next DATA : /n  Number Name Score /n"); scanf ( " %s " ,Num ); scanf ( " %s " ,Name ); scanf ( " %d" ,&score ); } return head ; } /*编写一个输出考生链表的函数 print () */ void print ( struct student *head ) { struct student *p = head ; printf ( "Number Name Score /n"); while ( p != NULL  ) { printf ( " %s " ,  p -> Num ); printf ( " %s " ,  p -> Name ); printf ( " %d ",  p -> score ); printf ( "/n" ) ; p = p -> next ; } } /*调用1， 2 两个函数， 并对其验证正确性 void main () { struct student *head ; head = creat ( ) ; print ( head ) ; } */ /*编写一个函数belongTo（） 函数，它负责检查一个指定的准考正号 是否已经存在链表中 ，如果已经存在，则返回在第几个节点，否则 返回0 */ int belongTo ( char Num[] ) { struct student *p , *head ; int count = 0 ; p = head ; while ( p && strcmp ( p -> Num ,Num)) { p = p -> next ; count++; } if ( !p ) return 0; return count; } /*第5题  */ struct student *insert ( struct student *head ) { struct student *p1 ,*min ,*p2 ,*New ; char Num[9]; int size = sizeof ( struct student ); p1 = head ; strcpy ( min -> Num , p1 -> Num ); p1 = p1 -> next ; while ( p1 -> next ) { if ( strcmp ( min -> Num , p1 -> Num ) > 0 ) { strcpy ( p2-> Num , min -> Num ); strcpy ( min -> Num , p1 -> Num ); strcpy ( p1 -> Num , min -> Num ) ; } p1 = p1 -> next ; } printf ( " please input a new data : /n " ); scanf ( " %s " ,&Num ) ; New = ( struct student * ) malloc ( size ) ; p1 = head ; strcpy ( New -> Num , Num ); while ( p1 -> next ) { if ( belongTo ( p1 -> Num ) != 0 ) { printf (" This number is not existed ,please reinput :/n "); scanf ( " %s " ,&Num ); strcpy ( p1 -> Num   , Num ); } p1 = p1 -> next ; } p1 = head ; if ( head == NULL ) { head = New ; New -> next = NULL ; } else { while ( (p1 -> next) && ( New -> Num > p1 -> Num ) ) { p2 = p1 ; p1 = p1 -> next ; } if ( New -> Num <= p1 -> Num ) { if ( head == p1 ) head = New ; else p2 -> next = New ; New -> next = p1 ; } else { p1 -> next = New ; New -> next = NULL ; } } return head ; } /*NO.6  */ struct student *Delete ( struct student *head ) { struct student *p1 ,*p2 ,*p3; char Num[9]; if ( head == NULL) { printf ( "/nlist null"); return head; } p1 = head ; printf ("please input a number : /n"); scanf ( "%s" , Num); if ( belongTo ( Num ) == 0) { printf ( "This number is not existed ,please reinput /n"); scanf ( "%s" , Num); }     //利用belongto函数进行检查 while ( strcmp ( p1 -> Num ,Num) && ( p1 -> next)) { p2 = p1 ; p1 = p1 -> next ; } if ( strcmp ( p1 -> Num ,Num) == 0)   //find the site { if ( head == p1 ) head = p1 -> next ; else p2 -> next = p1 -> next ; printf ( "Delete : %s /n" , Num); free ( p1 ); } return head ; } /*NO.7 */ void main () {     struct student *head;     int Num ,i ;     head = creat ( );     for ( i = 0 ; i < 35 ; i++ )  // to make the print beautiful printf ("*"); printf ("/n"); printf ( "  0 : Exit /n "); printf ( " 1 : Insert /n "); printf ( " 2 : Delete  /n "); printf ( " 3 : Display /n "); printf ( "Please input your choice ;/n "); scanf ( "%d", Num ); printf ( "/n" ); for ( i = 0 ; i < 35 ; i++ ) printf ("*"); switch ( Num ) { case 0 : exit ( 0 ); break; case 1 : insert ( head ); break; case 2 : Delete ( head ); break; case 3 : print ( head ); break; } }