decryption windows form app c++

char ch,mod;
char key = 97;
ifstream fin("Encrypted.txt",ios::binary);
    if(!fin)
    {
        MessageBox::Show("Couldn't open file : Encrypted.txt");
    }

    while(fin.get(ch))
    {
        if(ch==EOF)
        break;
        mod = ch + key;
        if (mod < 0) mod +=256;
    }