/*
  file3.c
  Author:  James Tam
  Version: January 12, 2010
  
  Assumptions: 
  1) The input file is in the following format
  <midterm gpa> <space> <final exam gpa> <assignment gpa>
  2) The maximum length of the name of the input file (and the path) 
  does not exceed 256 characters.

  This program will read numeric grade points from a file and based on 
  these values calculate a term letter grade. The user will be prompted to
  enter the name of the file at run time. The letter grades read from
  the input file will be then written to an output file called "letters.txt".
*/

#include <stdio.h>

int const MAX = 256;

int
main ()
{
  FILE *input_fp;
  FILE *output_fp;

  int midterm_exam;
  int final_exam;
  int assignments;
  float term_gpa;
  char letter;
  char input_file_name [MAX];

  printf ("Enter the name of the file that contains the numeric grade points: ");
  scanf ("%s", input_file_name);

  input_fp = fopen (input_file_name, "r");
  output_fp = fopen ("letters.txt", "w");

  if (input_fp == NULL)
    printf ("File '%s' cannot be opened.", input_file_name);
  else if (output_fp == NULL)
    printf ("Unable to open output file letters.txt for writing.");
  else
  {
    while (fscanf (input_fp, "%d", &midterm_exam) >= 0)
    {
      fscanf (input_fp, "%d", &final_exam);
      fscanf (input_fp, "%d", &assignments);
      term_gpa = (midterm_exam * 0.3) + (final_exam * 0.4) + (assignments * 0.3);
      
      /* JT's note: these cutoffs are for use in this program only and do not 
	 necessarily correspond to the ones used in the course. */
      if ((term_gpa <= 4) && (term_gpa > 3.5))
	letter = 'A';
      else if ((term_gpa <= 3.5) && (term_gpa > 2.5))
	letter = 'B';
      else if ((term_gpa <= 2.5) && (term_gpa > 1.5))
	letter = 'C';
      else if ((term_gpa <= 1.5) && (term_gpa > 0.5))
	letter = 'D';
      else if ((term_gpa <= 0.5) && (term_gpa >= 0))
	letter = 'F';
      else
	printf ("Error in gpa");
      printf ("%0.2f %c\n", term_gpa, letter);
      
      fprintf (output_fp, "%c\n", letter);
    } /* While: read from file */
    fclose (input_fp);
    fclose (output_fp);
  } /* Else: if program can read from the file. */
} /* End of the program. */