Bai mau doc ghi file

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define fio "Products.txt"
#define fbin "Products.dat"

typedef struct products{
    char Id[50], name[50];
    int quantity;   // so luong
    double cost;    // gia
} product;

void input(product prd[], int *n);
void writeBin(product prd[], int n);
void write(product prd[], int n);

void sort_cost(product prd[], int n);

void readBin(product prd[], int *n);
void output(product prd[], int n);

void search_id(product prd[], int n, char id[]);
void search_name(product prd[], int n, char name[]);
void search(product prd[], int n);


int main() {
    product prd[50];
    int n, i;
    FILE *f = fopen(fio, "r");

    int select;
    do {
        printf("Products:\n-----------------\n");
        printf("1: input\n2: read and sort by cost\n3: Search\n4: exit\n");
        printf("Enter the number to work: ");
        scanf("%d", &select);
        switch(select){
            case 1: {
                printf("1: INPUT\n");
                input(prd, &n);
                write(prd, n);
                break;
            }
            case 2: {
                printf("2: READ AND SORT BY COST\n");
                printf("Befor sort:\n--------------\n");
                readBin(prd, &n);
                output(prd, n);
                sort_cost(prd, n);
                write(prd, n);
                printf("After sort:\n--------------\n");
                readBin(prd, &n);
                output(prd, n);
                break;
            }
            case 3: {
                printf("SEARCH\n");
                search(prd, n);
                break;
            }
            case 4: return 0;
            default : printf("Error select !"); break;
        }
    }
    while (select != 4);
    return 0;
}

void input(product prd[], int *n){
    int i;
    char s[50];
    printf("Enter the number of products: ");
    scanf("%d", n);
    gets(s);
    printf("\n");
    for (i = 0; i < (*n); i++){
        printf("Enter the Id of products %d : ", i+1);
        gets(prd[i].Id);
        printf("\tEnter the nam of products %d : ", i+1);
        gets(prd[i].name);
        printf("\tEnter the quantity of products %d : ", i+1);
        scanf("%d", &prd[i].quantity);
        printf("\tEnter the cost of products %d : ", i+1);
        scanf("%lf", &prd[i].cost);
        gets(s);
    }
}

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

void write(product prd[], int n){
    int i;
    FILE *f = fopen(fio, "w");
    if(f==NULL) printf("Error load file");
    fprintf(f, "%-10s %-15s %-10s %-10s\n", "Id", "Name", "Quantity", "Cost");
    for (i = 0; i < n; i++)
        fprintf(f, "%-10s %-15s %-10d %-10.2lf\n", prd[i].Id, prd[i].name, prd[i].quantity, prd[i].cost);
    fclose(f);
    writeBin(prd, n);
    printf("input and write success to file!\n");
}

void sort_cost(product prd[], int n){
    int i, j;
    for (i = 0; i < n - 1; i++){
        for (j = i + 1; j < n; j++){
            if (prd[i].cost > prd[j].cost){
                product temp = prd[i];
                prd[i] = prd[j];
                prd[j] = temp;
            }
        }
    }
}

void output(product prd[], int n){
    int i;
    printf("%-10s %-10s %-15s %-10s %-10s\n", "Order", "Id", "Name", "Quantity", "Cost");
    for (i = 0; i < n; i++)
        printf("%-10d %-10s %-15s %-10d %-10.2lf\n", i + 1, prd[i].Id, prd[i].name, prd[i].quantity, prd[i].cost);
}



void readBin(product prd[], 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(product); //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(prd,sizeof(product),(*n),f);
    fclose(f);
}

void search_id(product prd[], int n, char id[]){
    int i, check = 0;
    for (i = 0; i < n; i++){
        if (strcmp(id, prd[i].Id) == 0){
            check = 1;
            printf("%-10s %-10s %-15s %-10s %-10s\n", "Order", "Id", "Name", "Quantity", "Cost");
            printf("%-10d %-10s %-15s %-10d %-10.2lf\n", i + 1, prd[i].Id, prd[i].name, prd[i].quantity, prd[i].cost);
            break;
        }
        if (check == 0 && i == n - 1)
            printf("Not found product have Id is %s !\n", id);
    }
}

void search_name(product prd[], int n, char name[]){
    int i, check = 0;
    for (i = 0; i < n; i++){
        if (strcmp(name, prd[i].name) == 0){
            check = 1;
            printf("%-10s %-10s %-15s %-10s %-10s\n", "Order", "Id", "Name", "Quantity", "Cost");
            printf("%-10d %-10s %-15s %-10d %-10.2lf\n", i + 1, prd[i].Id, prd[i].name, prd[i].quantity, prd[i].cost);
            break;
        }
        if (check == 0 && i == n - 1)
            printf("Not found product have name is %s !\n", name);
    }
}

void search(product prd[], int n){
    int select;
    char s[50];
    do{
        printf("\t1: Id\n\t2: Name\n\t3: exit search\nEnter the type you want search: ");
        scanf("%d", &select);
        gets(s);
        switch(select){
            case 1: {
                printf("Enter Id want search: ");
                char id[50];
                gets(id);
                search_id(prd, n, id);
                break;
            }
            case 2: {
                printf("Enter name want search: ");
                char name[50];
                gets(name);
                search_name(prd, n, name); break;
            }
            case 3: return;
            default : printf("Error select !"); break;
        }
    }while (select != 3);
}