File allocation table (FAT8) implementation error in C++?

Question

I am trying to simulate FAT8 File_Allocation_Table. FAT entries varies from -1 to 255 inclusive. Directory entry contains starting address of FAT table for a particular directory.

Whenever the starting address is greater than 127 then it's give a negative number. Negative number can be converted to +ve number by using offset. But the problem become hard for me when entry contains -1 and 255 since both gives same value.

How to handle this case ?

#include<bits/stdc++.h>
#define SIZE 256 
using namespace std;

struct Dir{
    char fname[SIZE]; //File Name 
    char start;//1st entry in FAT
    char end;//Last entry in FAT
}dir;

char FAT[SIZE];
int NoOfFile;
char dfname[ ]="dir.txt";

int main(){
    ofstream fout;
    ifstream fin;
    char name[256];
    cout<<"Enter file name\n";
    cin>>name;
    dir.start=255;
    dir.end=3;
    strcpy(dir.fname,name);

    fout.open(dfname);
    fout.write((char*)&dir,sizeof(dir));
    fout.close();

    fin.open(dfname);
    fin.read((char*)&dir,sizeof(dir));
    cout<<dir.fname<<" "<<(int)dir.start<<" "<<(int)dir.end<<"\n";
    fin.close();
    return 0;
}