[Cau 2 De 1] Nhap Xuat Sua file trong C

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define fbin "thieumao.txt"

typedef struct DanhSach{
    char Ho_ten[50], Que[50];
    float Diem_TB;
} DS;

void input(DS sv[], int *n);
void writeBin(DS sv[], int n);
void readBin(DS sv[], int *n);

int main() {
    DS sv[50];
    int n, i;

    int select;
    do {
        printf("1: Nhap\n2: Xuat\n3: Sua\n4: Thoat\n");
        printf("Enter the number to work: ");
        scanf("%d", &select);
        switch(select){
            case 1: {
                printf("DOC\n");
                input(sv, &n);
                writeBin(sv, n);
                break;
            }
            case 2: {
                printf("XUAT\n");
                readBin(sv, &n);
                output(sv, n);
                break;
            }
            case 3: {
                printf("SUA\n");
                readBin(sv, &n);
                int i;
                printf("Nhap STT sinh vien can sua Diem_TB: ");
                scanf("%d",&i);
                printf("Nhap Diem_TB: ");
                scanf("%1f", &sv[i-1].Diem_TB);
                writeBin(sv, n);
                printf("\nSAU KHI SUA:\n");
                output(sv, n);
                break;
            }
            case 4: return 0;
            default : printf("LOI\n"); break;
        }
    }
    while (select != 4);
    return 0;
}

void input(DS sv[], int *n){
    int i;
    char s[50];
    printf("Nhap so luong sinh vien: ");
    scanf("%d", n);
    gets(s);
    printf("\n");
    for (i = 0; i < (*n); i++){
        printf("\nNhap sinh vien thu %d \n",i+1);
        printf("\tHo ten: ");
        gets(sv[i].Ho_ten);
        printf("\tQue: ");
        gets(sv[i].Que);
        printf("\tDiem TB: ");
        scanf("%1f", &sv[i].Diem_TB);
        gets(s);
    }
}

void writeBin(DS sv[], int n){
    FILE *f = fopen(fbin,"wb");;
    int i;
    if(f==NULL) printf("Error load file");
    else fwrite(sv,sizeof(DS),n,f);
    fclose(f);
}

void readBin(DS sv[], int *n){
    FILE *f = fopen(fbin,"rb");
    fseek(f,0,SEEK_END); //Nhay ve cuoi file, di chuyen di 0 vi tri
    (*n) = (ftell(f)+1)/sizeof(DS); //ftell(); tra ve vi tri hien tai cua con tro
    // SEEK_CUR: di chuyen bat dau tu vi tri hien tai cua con tro, chi dung trong fseek()
    fseek(f,0,SEEK_SET); //Nhay ve dau file, di chuyen di 0 vi tri
    fread(sv,sizeof(DS),(*n),f);
    fclose(f);
}

    char Ho_ten[50], Que[50];
    float Diem_TB;

void output(DS sv[], int n){
    int i;
    printf("%-10s %-10s %-15s %-10s\n", "STT", "Ho_ten", "Que",  "Diem_TB");
    for (i = 0; i < n; i++)
        printf("%-10d %-10s %-15s %-10.2lf\n", i + 1, sv[i].Ho_ten, sv[i].Que, sv[i].Diem_TB);
}