Before:

sum = count = 0;
do
{ 
    cout << "Enter the next number and -1 to end the sequence" << endl;
    cin >> number; 

    if( number != -1 )
    {
        sum += number;
	count++;
    }
    else
    {
        average = sum / count;
        cout << "The average of " << count << " numbers is " << average << endl;
    }
} while( number != -1 );