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

#define MAX_STR  32

typedef struct Student {
  char            name[MAX_STR];
  char            major[MAX_STR];
  struct Student *next;
} StudentType;


// These are the functions used in the main function.
// They are defined here since the main function appears
// before them.
void createStudent(char*, char*, StudentType**);
void printStudent(StudentType*);
void freeList(StudentType*);


int main() {
  StudentType *ourClassroom = NULL;
  StudentType *currStudent;
  char         str1[MAX_STR];
  char         str2[MAX_STR];

  printf("\nEnter student names and their majors (use -1 when done): ");
  while(1) {
    printf("\nEnter name: ");
    scanf("%s", str1);
    if (strcmp(str1, "-1") == 0)
      break;
    printf("Enter major: ");
    scanf("%s", str2);

    createStudent(str1, str2, &currStudent);
    
    currStudent->next = ourClassroom;
    ourClassroom = currStudent;
  }

  printf("\nHere is the list:\n");
  printf("%-15s %-15s\n", "NAME","MAJOR");
  printf("--------------- ---------------\n");

  currStudent = ourClassroom;
  while(currStudent != NULL) {
    printStudent(currStudent);
    currStudent = currStudent->next;
  }
  freeList(ourClassroom);
}

// Allocates memory for a new student and initializes it with the given data
void createStudent(char *name, char *major, StudentType **student) {
  *student = (StudentType *) malloc(sizeof(StudentType));
  if (student == NULL) { 
    printf("Memory allocation error\n"); 
    exit(0); 
  }
  strcpy((*student)->name,  name);
  strcpy((*student)->major, major);
  (*student)->next = NULL;
}

// Prints a single student's information
void printStudent(StudentType *sPtr) {
  printf("%-15s %-15s\n", sPtr->name, sPtr->major);
}

// Free all items in a Singly-Linked List 
void freeList(StudentType *listItem) {
  StudentType *nextItem;
  
  while(listItem != NULL) {
    nextItem = listItem->next;
    free(listItem);
    listItem = nextItem;
  }
}