File allocation table

#include <stdio.h>
#include <conio.h>
#include <alloc.h>
#include <dos.h>
#include <bios.h>

struct boot
{
    unsigned char jump[3] ;
    char OEMname[8] ;
    short int bps ;
    unsigned char spc ;
    short int reservedsec ;
    unsigned char fatcopies ;
    short int maxdirentries ;
    short int totalsec ;
    unsigned char mediadesc ;
    short int secperfat ;
    short int secpertrack ;
    short int noofsides ;
    long int hidden ;
    long int hugesec ;
    unsigned char drivenumber ;
    unsigned char reserved ;
    unsigned char bootsignature ;
    long int volumeid ;
    char volumelabel[11] ;
    char filesystype[8] ;
    unsigned char unused[450] ;
} ;

struct boot bs ;
char filetypestr[8] ;

void getfat_12 ( unsigned char * ) ;
void read_fat_info ( long ) ;
void fat_info( ) ;

void main( )
{
    char choice ;

    clrscr( ) ;

    printf ( \"A. Drive A\" ) ;
    printf ( \"\\nC. Drive C\" ) ;
    printf ( \"\\n0. Exit\" ) ;

    printf ( \"\\nEnter the drive (A/C): \" ) ;
    scanf ( \"%c\", &choice ) ;

    if ( absread ( choice - 65, 1, 0, &bs ) == -1 )
    {
        printf ( \"Error reading sector\" ) ;
        exit ( 0 ) ;
    }
    else
    {
        strcpy ( filetypestr, bs.filesystype ) ;
        filetypestr[6] = \'\\0\' ;
    }

    fat_info( ) ;
}

void getfat_12 ( unsigned char *pfat )
{
    int value ;
    int *fatentry ;
    int i, k ;

    for ( k = 2 ; k < 18 ; k++ )
    {
        i = k * 3 / 2 ;

        fatentry =  ( int* ) ( pfat + i ) ;

        if ( ( k % 2 ) == 0 )
            value = ( *fatentry & 0x0fff ) ;
        else
            value = ( *fatentry >> 4 ) ;

        printf ( \"%03x   \", value ) ;
        if ( k % 9 == 0 )
            printf ( \"\\n\" ) ;
    }
}

void read_fat_info ( long fat_num )
{
    int j, i ;

    unsigned char *p ;

    if ( strncmp ( \"FAT12\", filetypestr, 5 ) == 0 )
    {
        p = ( unsigned char* ) malloc ( bs.bps ) ;
        absread ( 0, 1, fat_num, p ) ;
        getfat_12( p ) ;
    }

    if ( strncmp ( \"FAT16\", filetypestr, 5 ) == 0 )
    {
        short int *pfat ;
        p = ( unsigned char* ) malloc ( bs.bps ) ;
        absread ( 2, 1, fat_num, p ) ;
        pfat = ( short int* ) p ;

        for ( j = 0 ; j < 2 ; j++ )
        {
            printf ( \"\\n%d   \", j * 8 ) ;
            for ( i = 0 ; i < 8 ; i++ )
            {
                printf ( \"%04x  \", *pfat++ ) ;
            }
        }
    }
}

void fat_info( )
{
    long int first_fat, second_fat ;

    first_fat = bs.reservedsec ;
    second_fat = bs.reservedsec + bs.secperfat ;

    printf ( \"\\n%s Fat Information\", filetypestr ) ;
    printf ( \"\\n-------------------------------\" ) ;

    printf ( \"\\nFirst FAT Information\\n\" ) ;

    read_fat_info ( first_fat ) ;

    printf ( \"\\n\\nSecond FAT Information\\n\" ) ;

    read_fat_info ( second_fat ) ;
    printf ( \"\\n-------------------------------\\n\" ) ;
}