#include <stdio.h>
#include <stdlib.h>

#define MAX_ID 6
#define MAX_NAME 21
#define EQUAL 0

typedef struct date {
   int dd;
   int mm;
   int yy;
} Date;


typedef struct student{
   char studentID[MAX_ID];    /* A 5 character unique ID eg. 'S1234' */
   char lastName[MAX_NAME];   /* Stores Last Name. No spaces!        */
   char firstName[MAX_NAME];  /* Stores rest of the name, inc. spaces*/
   Date birthday;             /* store the birthday of the student */
} StudentType;

typedef struct studentlistnode {
   StudentType student;
   struct studentlistnode *next;
} StudentListNode;

typedef StudentListNode * StudentListNodePtr;

extern StudentListNodePtr NewStudent(char *studentID, char* lastName,
                                     char *firstName, Date birthday);
extern StudentListNodePtr AddStudent(StudentListNodePtr newStudent,
                                     StudentListNodePtr head);

extern StudentListNodePtr DelStudent(char* studentID, StudentListNodePtr head);

#include "student.h"

/* function implementation goes here */
/**/
StudentListNodePtr NewStudent(char *studentID, char* lastName,
                              char *firstName, Date birthday) {

  StudentListNodePtr newN = malloc(sizeof(StudentType));
  
  strncpy(newN->student.studentID, studentID, MAX_ID);
  
  strncpy(newN->student.lastName, lastName, MAX_NAME);
  strncpy(newN->student.firstName, firstName, MAX_NAME);
  newN->student.birthday = birthday;
  
  newN->next = NULL;
  return newN;
}

/*add student*/
StudentListNodePtr AddStudent(StudentListNodePtr newStudent,
                              StudentListNodePtr head) {
  
  StudentListNodePtr currentStudent;
  currentStudent = head;
  
  if(head == NULL){
    /*newStudent->next = head;*/
    head = newStudent;
    }
  else {
    
    while(currentStudent->next!=NULL)
      currentStudent = currentStudent->next;
    
      currentStudent->next = newStudent;
  }
  return head;
}

/*delete student*/
StudentListNodePtr DelStudent(char* studentID, StudentListNodePtr head)
{
  StudentListNodePtr prevStudent, curStudent, temp;
  temp = NULL;
  curStudent = head;
  prevStudent = NULL;

  if(strcmp(head->student.studentID, studentID) == EQUAL) {
    temp = head;
    head = head->next;
    free(temp);                     /*============>error is right here*/
  }
  else {
    while(curStudent != NULL) {
      if(strcmp(curStudent->student.studentID, studentID) == EQUAL) {
    temp = curStudent;
        prevStudent->next = curStudent->next;
    free(temp);                /*==============>error is right here*/
      }
      else {
        prevStudent = curStudent;
        curStudent = curStudent->next;
      }
    }
  }
  return head;
}