// Fig. 2.9: fig02_09.cpp
// Class average program with sentinel-controlled repetition.
#include <iostream>
     
using std::cout;
using std::cin;
using std::endl;
using std::fixed;
                                                                   
#include <iomanip>        // parameterized stream manipulators
                                                                  
using std::setprecision;  // sets numeric output precision    
    
// function main begins program execution
int main()
{
  int total;         // sum of grades
  int gradeCounter;  // number of grades entered
  int grade;         // grade value
    
  double average;    // number with decimal point for average
    
  // initialization phase
  total = 0;         // initialize total
  gradeCounter = 0;  // initialize loop counter
    
  // processing phase
  // get first grade from user
  cout << "Enter grade, -1 to end: ";  // prompt for input
  cin >> grade;                        // read grade from user
    
  // loop until sentinel value read from user
  while ( grade != -1 ) {                  
    total = total + grade;            // add grade to total
    gradeCounter = gradeCounter + 1;  // increment counter
          
    cout << "Enter grade, -1 to end: ";  // prompt for input
    cin >> grade;                        // read next grade
    
  } // end while
    
  // termination phase
  // if user entered at least one grade ...
  if ( gradeCounter != 0 ) {
          
    // calculate average of all grades entered
    average = static_cast< double >( total ) / gradeCounter;
         
    // display average with two digits of precision
    cout << "Class average is " << setprecision( 2 )
	 << fixed << average << endl;
    
  } // end if part of if/else
    
  else // if no grades were entered, output appropriate message
    cout << "No grades were entered" << endl;
    
  return 0;   // indicate program ended successfully
    
} // end function main