cây nhị phân sinh viên

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

struct item{
    char id[20];
    char name[20];
    double scores;
};
struct Node
{
     item key; //truong key cua du lieu
     Node *Left, *Right; //con trai va con phai
};
typedef Node *Tree;  //cay

int compare(item x, item y){ // so sanh 2 item theo key
    return strcmp(x.id, y.id);
}

item inputItem(){   // nhap 1 item
    item x;
    char id[20];
    printf("Enter id of student (q to quit): ");
    gets(x.id);

    if(strcmp(x.id, "q") == 0 || strcmp(x.id, "Q") == 0){
        return x;
    }

    printf("Enter name of student: ");
    gets(x.name);

    printf("Enter scores of student:");
    scanf("%lf", &x.scores);

    //fflush(stdin);
    while (getchar() != '\n');

    return x;
}

void outItem(item x){
    printf("%-20s %-20s %-3.2f \n", x.id, x.name, x.scores);
}

int insertNode(Tree &T, item x) // chen 1 Node vao cay
{
    if (T != NULL)
    {
        if (compare(T->key, x) == 0) return -1;  // Node nay da co
        if (compare(T->key, x) > 0) return insertNode(T->Left, x); // chen vao Node trai
        else if (compare(T->key, x) < 0) return insertNode(T->Right, x);   // chen vao Node phai
    }
    T = (Node *) malloc(sizeof(Node));
    if (T == NULL) return 0;    // khong du bo nho
    T->key = x;
    T->Left = T->Right = NULL;
    return 1;   // ok
}

void CreateTree(Tree &T)        // nhap cay
{
    item x;
    while (1)
    {
        printf("Enter a student: ");
        x = inputItem();
        if (strcmp(x.id, "q") == 0 || strcmp(x.id, "Q") == 0) break;  // x = 0 thi thoat
        int check = insertNode(T, x);
        if (check == -1) printf("Student is exits!");
        else if (check == 0) printf("Memory full");

    }
}

// Duyet theo LNR
void LNR(Tree T)
{
     if(T!=NULL)
     {
          LNR(T->Left);
          outItem(T->key);
          LNR(T->Right);
     }
}

Node* searchKey(Tree T, int scores)     // tim nut co diem < 4
{
    if (T!=NULL)
    {
        if (T->key.scores < scores) { Node *P = T; return P;}
        if (T->key.scores >= scores) {
            Node *node = searchKey(T->Left, scores);
            if(node != NULL) return node;
            else {
                return searchKey(T->Right, scores);
            }
        }
    }
    return NULL;
}

int delKey(Tree &T, item x)     // xoa nut co key x
{
    if (T==NULL) return 0;
    else if (compare(T->key, x) > 0) return delKey(T->Left, x);
    else if (compare(T->key, x) < 0) return delKey(T->Right, x);
    else // T->key == x
    {
        Node *P = T;
        if (T->Left == NULL) T = T->Right;    // Node chi co cay con phai
        else if (T->Right == NULL) T = T->Left;   // Node chi co cay con trai
        else // Node co ca 2 con
        {
            Node *S = T, *Q = S->Left;
            // S la cha cua Q, Q la Node phai nhat cua cay con trai cua P
            while (Q->Right != NULL)
            {
                S = Q;
                Q = Q->Right;
            }
            P->key = Q->key;
            S->Right = Q->Left;
            delete Q;
        }
    }
    return 1;
}


int main()
{
    Tree T;
    T=NULL; //Tao cay rong

    CreateTree(T); //Nhap cay
    //duyet cay
    printf("LNR: \n");
    LNR(T);
    printf("\n");

    Node *P;
    item x;
    printf("Enter id of student to add: ");
    x = inputItem();
    if (insertNode(T, x) == -1){
        printf("add failt!");
    }else{
        printf("add success:\n");
        printf("LNR: \n");
        LNR(T);
        printf("\n");
    }


    int del = 1;
    while(del){
        Node* node = searchKey(T, 4);
        if(node != NULL){
            printf("del");
            del = delKey(T, node->key);
        }else{
            printf("null");
            del = 0;
        }
    }
    printf("LNR: \n");
    LNR(T);
    printf("\n");
    return 0;
}