// loop to calc. grade for each student
#include <iostream>
using namespace std;
int getInfo(int&, int&);//use reference var to change values
char calcGrade(int, int); //values: not to be changed
int main()
// loop until getInfo returns false 
{ int midterm, final;
  char grade;
  while (getInfo(midterm,final))
  { grade = calcGrade(midterm, final);
    cout<<"Grade = "<<grade<<"\n";
  } // while loop 
  return 0;
} // main 
		
int getInfo(int &mid, int &fin)
// get midterm and final grade 
{ cout<<"Enter midterm grade: (-1 to end)";
  cin>>mid;  
  if (mid < 0 )
    return 0; // signal end of data by returning false 
  else        // valid midterm get final & return true 
  {  cout<<"Enter final grade: ";
     cin>>fin; 
     return 1;
  } // valid midterm 
} // getInfo 
		
char calcGrade(int mid, int fin)
// calculate average, return letter grade 
{ int avg;
  char grade='F'; //pessimistic method
  avg = (int)((mid + fin+1.0)/2.0);// rounds to nearest int 
  if (avg >= 65) grade= 'D';
  if (avg >= 70) grade= 'C';
  if (avg >= 80) grade= 'B';
  if (avg >= 90) grade= 'A';
  return grade;
} // calcGrade