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

// structure definition
struct node {
    char name[50];
    int age;
    int student_no;
    char nationality[50];
    struct node *next;
};
typedef struct node *NODE_T;

// function declarations
void enter_new_data();
void remove_existing_data();
void display_all_data();
void show_options();
NODE_T getnode();
void freenode(NODE_T p);
void free_buffer();
void continue_f(char message[100]);

// global variables
char ch;

// create linked-list's main holder variable
NODE_T students,conductor;

int main(){

    // allocate memory for the node link-list holder
    students = NULL;
    //students->next = 0; // initialize next to 0 for first node of linked-list

    // show the options that user has
    show_options();

    return 1;
}

// this function will list options that user can apply
void show_options(){

    system("cls"); // clear screen

    int opt,opt_bool=0;

    printf("%s\n\n%s\n%s\n%s\n%s\n\n","The Options You Have","1. Add New Student's Record","2. Delete An Existing Student's Record","3. Display The List Of Students","4. Exit");


    while(opt_bool != 1){
        printf("Operation:  ");
        scanf("%d",&opt);

        if(opt == 1 || opt == 2 || opt == 3 || opt == 4){
            opt_bool = 1;
        }

    }

    // check the operation and go to the operation
    if(opt == 1){ // adding record
        enter_new_data();
    } else if(opt == 2){ // removing record

    } else if(opt == 3){ // displaying records
        display_all_data();
    } else if(opt == 4){ // exit the program
        exit(0);
    }
}

// enter new student data into linked-list
void enter_new_data(){

    system("cls"); // clear screen

    // get a new node
    NODE_T p = getnode();

    printf("You are entering a new student's record\n");

    // take student's name
    printf("Student's Name: ");
    scanf("%s",p->name);
    free_buffer();

    // take student's age
    printf("Student's Age: ");
    scanf("%d",&p->age);
    free_buffer();

    // take student's number
    printf("Student's Number: ");
    scanf("%d",&p->student_no);
    free_buffer();

    // take student's nationality
    printf("Student's Nationality: ");
    scanf("%s",p->nationality);
    free_buffer();

    // set p->next next value of last node of linked-list, which is equal to 0
    p->next = 0;

    printf("%s, %d, %d, %s",p->name,p->age,p->student_no,p->nationality);


    // if there is no any node yet, add node p as first node
    if(students == NULL) {
        students = p;
    } else {

        conductor = students; // assign linked-list to the conductor to traverse

        // reach the last node
        while (conductor->next != 0)
        {
            conductor = conductor->next;
        }

        conductor->next = p; // append the node p to the linked list
    }

    freenode(p); // set free node p

    continue_f("Adding new record is done."); // ask press any key to continue

    show_options(); // show options

}

// to display all data of linked list
void display_all_data(){

    system("cls"); // clear screen

    printf("The Student Records\n\n");

    printf("%s%7s%18s%15s","STUDENT'S NAME","AGE","STUDENT NUMBER","NATIONALITY"); // captions

    freenode(conductor);
    conductor = getnode();
    conductor = students; // assign linked-list to the conductor to traverse

    if (conductor != NULL ) { /* Makes sure there is a place to start */
        // traverse untill last node
        while ( conductor->next != 0)
        {

            printf("\n%s%7d%18d%15s",conductor->name,conductor->age,conductor->student_no,conductor->nationality); // record

            conductor = conductor->next;
        }
    } else {
        printf("\n\n There is not any record yet.");
    }

    continue_f("Listing records is done."); // ask press any key to continue

    show_options(); // show options
}

// create new node
NODE_T getnode(void){
    NODE_T p;
    p = (struct node *) malloc(sizeof(struct node));
    return p;
}

// set free a node
void freenode(NODE_T p){
    free(p);
}

// clear the buffer if there are any extra data in it
void free_buffer(){
    while (getchar() != '\n') { }
}

void continue_f(char message[100]){
    printf("\n\n%s\nPress any key to continue...",message);
    getch(); // wait for pushing any key from user
}