Thread: Need help with my program

Hey guys I'm new to this board, but if you guys could share a little insight I would appreciate it. Now the program is for figuring fuel mileage.

Code:

#include <iostream>

using std::cout;
using std::cin;
using std::endl;


#include <iomanip>



 // main function begins
int main()
{ 

 
	double gal; //gallons used
	int miles; //miles driven
	double mpg; //mpg
	int counter;//counter used
	double total; //total of miles
    double average; //overall average

	total = 0;
	counter = 0;


	cout << "Enter the gallons used (-1 to end): ";
	cin >> gal;

	cout << "Enter the miles driven ";
	cin >> miles;

	mpg = miles / gal;
		cout << "The miles / gallon for this tank was " << mpg << endl;

		while ( gal != -1 ) {
		total = total + gal;
		counter = counter + 1;

		cout << "Enter the gallons used (-1 to end) "; 
		cin >> gal;
		cout << "Enter the miles driven ";
		cin >> miles;
		
		mpg = miles / gal;
		cout << "The miles / gallon for this tank was " << mpg << endl;

		
		}
		if ( gal != 0 ) {
			average = ( double) total  / counter;

			cout << "The overall average miles/gallon was " << average <<endl;
		}
		
		
		else
			cout << " No data was entered" << endl;
		
				
		return 0;
}

Now what happens is, I can input the gallons used and miles travedeled over and over, and it will give me the the miles/gallon answer which is correct. But as soon as I hit -1 to end the program it will continue asking for the gal's used and miles driven. It should terminate right after I hit -1. What have I done wrong? Is it my while statement that is incorrect? I've tried several different ways and nothing works. The program has no errors at all, so it must be a incorrect operator or misplacement.

Thanks

Thanks man...yeah I went to the wrong forum....DOH

The problem is that while loops don't check until the very end, thus everything between when you enter -1 and the bracket will still run. You need to do one of two things:

Code:

while (gal!=-1
{
   cout << "Enter the gallons used (-1 to end) "; 
   cin >> gal;
   if (gal==-1)
       break;
   etc

or do something like this:

Code:

// ask for gallons
while (gal!=-1)
{
     // get miles then print mpg
     // ask for gallons
}