while loop problem

Hey,

I find with all my programmes I write, if I have two inputs to enter, within the while loop, it wont end until the last input has been put in, in the past I went round it the long way by putting an 'if' statment in to break the loop after the first input, but what is the correct way to solve this problem, I had a quick look at the QA's and the Search thing, but not much luck

Code:

	while (( miles != -1) || ( liters != -1 ))
	{
	cout << "Please enter number of miles you have driven or -1 to quit" << endl;
	cin >> miles;
	cout << "Please enter number of liters you put in your car to fill it up" << endl;
	cin >> liters;
	answer = compute(liters, miles);

	cout << "You have travled " << answer << " miles per gallon" << endl;
	}
	return 0;

Thanks, ps not homework as I am only teaching myself, in the UK I can never find any (cheap) lessions on C++ anyway.

Actually, since you state the part about entering -1 only at the prompt for miles, you'll only need to test miles.
So the loop condition becomes (miles != -1)

THe quirk with the way you do it might be that a user could enter -1 for miles, and then still be greeted with a prompt for liters.
An alternative to fix this might be to use an infinite loop, breaking out of it if miles is tested to be -1.

Code:

//loop ends when miles == -1
for (;;) {
	//prompt for miles, enter -1 to quit
	cin >> miles;
	if (miles == -1)
		break; //end loop here!
	//prompt for liters
	cin >> liters;
	//compute answer
	//print result
}

Code:

cout << "Please enter number of miles you have driven or -1 to quit" << endl;
cin >> miles;
while ( miles != -1 )
{
    cout << "Please enter number of liters you put in your car to fill it up" << endl;
    cin >> liters;

    answer = compute(liters, miles);
    cout << "You have travled " << answer << " miles per gallon" << endl;

    cout << "Please enter number of miles you have driven or -1 to quit" << endl;
    cin >> miles;
}
return 0;