Program to count number of used cluster in first 100 cluster

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

struct BOOT {  //for FAT16
    char jmp[3];
    char OEM[8];
    int bytes_per_sector;
    char sectors_per_cluster;
    int reserved;
    char FAT_cnt;
    int ROOT_size;
    int total_sectors;
    char media;
    int FAT_size;
    int sectors_per_track;
    int head_cnt;
    long hidden_sectors;
    long total_sectors_long;
    char unknown[3];
    long serial;
    char volume[11];
    char FAT_type[8];
    char loader[448];
    char mark[2];
};

struct ROOT {
    char name[8];
    char ext[3];
    char attr;
    char reserved[10];
    char time[2];
    char date[2];
    int first_cluster;
    long size;
};

void main()
{]
    int i;
    int drive = 3; //A=0, B=1, C=2, D=3 ...

    //Reading boot sector from disk D
    BOOT boot;

    int res = absread(drive, 1, 0, &boot);


    //Reading FAT16 table from disk D
    unsigned int *fat = (unsigned int *)malloc (boot.FAT_size * boot.bytes_per_sector);


    res = absread(drive, boot.FAT_size, boot.reserved, fat);
    if(res != 0){
        printf("Cannot read FAT\n");
        return;
    }
    //Counting number of used clusters from first 100 clusters
    int used_count = 0;
    for (i = 2; i < 100; i++){ //first 2 clusters are not used
        if(fat[i] != 0) used_count++;
    }
    printf("\n");
    printf("Number of used clusters from first 100 clusters:");
    printf("%d\n", used_count);



    getchar();
}