Program to display content of first 30 non-empty FAT cell

#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 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);
    unsigned int *fat = (unsigned int *)malloc (boot.FAT_size * boot.bytes_per_sector);
    //printing first 30 non-empty FAT cells
    printf("Content of first 30 non-empty FAT cells:");
    int i = 0, num = 0;
    int total = 30;
    while(num<total){
        if(fat[i]!=0){
            printf("%u ", fat[i]);
            num++;
        }
        i++;

    getchar();
}