No Operator error code - c++

Question

I am completing a hotel reservation form using C++ language. I keep getting no operator error for fin !=0. How can I address this error? Here is the actual coding...
void Hotel::show_room_record()
{
cout << "R.Num" << setw(10) << "R.Stat" << setw(10) << "Category" << setw(10) << "Rent\n";
ifstream fin("room.dat", ios::in);
for (int p = 0; fin != 0; p = p + 15)
{
fin.seekg(p);
fin >> room_no;
fin >> room_status;
fin >> category;
fin >> rent;
cout << room_no << setw(10) << room_status << setw(10) << category << setw(10) << rent << "\n";
}
fin.close();
}

Answer 1

You can't compare fin with 0, fin wont return the next input.
First store the input in a variable, then compare it.
For your case, you probably want to check if the next character is a '0', or even a '\0'.
Try using this:
http://www.cplusplus.com/reference/istream/istream/peek/
Your condition becomes (assuming you want '\0'):
fin.peek() != 0

Answer 2

You cannot test fin != 0. fin isn't a number, to testing for equality with 0 makes about as much sense as testing what kind of orange an apple is. You can test that fin is still readable though with a simple fin by taking advantage of operator bool, but that's tricky because the test for is readable will be made before reading. You can't test for failure before you have a chance to fail and that leaves open the possibility that the last reads failed and were not checked for validity.
Instead of trying to fix this, I'm going to go all X-Y on you here and suggest something completely different.
Define a structure
struct room
{
int room_no;
string room_status;
string category;
int rent; // could be a float. Don't care much for this example
// that said, watch out for rounding errors when dealing with floats
};
Create a function that makes it really easy to read into this structure
std::istream & operator>>(std::istream & in,
room & inroom)
{
in >> inroom.room_no >> inroom.room_status >> inroom.category >> inroom.rent;
return in;
}
Create a function that makes it really easy to write this structure
std::ostream & operator<<(std::ostream & out,
const room & outroom)
{
out << outroom.room_no << setw(10) << outroom.room_status <<
setw(10) << outroom.category << setw(10) << outroom.rent;
return out;
}
Make a std::vector of the above structure a member of the Hotel class
std::vector<room> rooms;
Read the file into it
room temp;
while (in >> temp)
{
rooms.push_back(temp);
}
Now the hotel knows the status of all the rooms without having to keep looking at the file. This makes printing easy.
for(room & r: rooms)
{
cout << r << '\n';
}
It makes finding any room a simple traversal of rooms
for(room & r: rooms)
{
if (r.whatever == desiredwhatever)
{
return r;
}
}
and every now and then you rewrite the file if a room was changed.
std::ostream outfile("path to file goes here");
for(room & r: rooms)
{
if (!(outfile << r << '\n'))
{
//handle error
}
}
All of these things you probably have to do anyway. The only downside is if you are not allowed to use std::vector. In that case you either write a simple vector substitute or use an array and pray it never overflows.