#include <stdio.h>

//	Function Declarations
int getStu     (FILE* spStu,
                int* stuID, int*  exam1,
                int*  exam2, int* final);
int writeStu   (FILE* spGrades,
                int   stuID, int   avrg,  char grade);
void calcGrade (int   exam1, int   exam2, int  final,
                int*  avrg,  char* grade);

int main (void)
{
//	Local Declarations
	FILE* spStu;
	FILE* spGrades;

	int stuID;
	int exam1;
	int exam2;
	int final;
	int avrg;

	char grade;

//	Statements
	printf("Begin student grading\n");
	if (!(spStu = fopen ("stu_grades.txt", "r")))
	   {
	    printf("\aError opening student file\n");
	    return 100;
	   } // if open input

	if (!(spGrades = fopen ("P07-06Gr.DAT", "w")))
	   {
	    printf("\aError opening grades file\n");
	    return 102;
	   } // if open output

	while (getStu (spStu, &stuID, &exam1, &exam2, &final))
	   {
	    calcGrade (exam1, exam2, final, &avrg, &grade);
	    writeStu  (spGrades, stuID, avrg, grade);
	   } // while

	fclose (spStu);
	fclose (spGrades);

	printf("End student grading\n");
	return 0;
}	// main

/* ======================== getStu =======================
	Reads data from student file.
	   Pre   spStu is an open file.
	         stuID, exam1, exam2, final pass by address
	   Post  reads student ID and exam scores
	         if data read   --returns 1
	         if EOF or error--returns 0
*/
int getStu (FILE* spStu, int* stuID, int* exam1,
            int*  exam2, int* final)
{
//	Local Declarations
	int ioResult;

//	Statements
	ioResult = fscanf(spStu, "%d%d%d%d", stuID,
	                  exam1, exam2, final);
	if (ioResult == EOF)
	    return 0;
	else if (ioResult != 4)
	   {
	    printf("\aError reading data\n");
	    return 0;
	   } // if
	else
	   return 1;
}	// getStu

/*	==================== calcGrade ===================
	Determine student grade based on absolute scale.
	   Pre   exam1, exam2, and final contain scores
	         avrg and grade are addresses of variables
	   Post  Average and grade copied to addresses
*/
void calcGrade (int  exam1, int   exam2, int final,
                int* avrg,  char* grade)
{
//	Statements
	*avrg = (exam1 + exam2 + final) / 3;
	if (*avrg >= 90)
	   *grade = 'A';
	else if (*avrg >= 80)
	   *grade = 'B';
	else if (*avrg >= 70)
	   *grade = 'C';
	else if (*avrg >= 60)
	   *grade = 'D';
	else
	   *grade = 'F';
	return;
}	// calcGrade

/*	===================== writeStu ====================
	Writes student grade data to output file.
	   Pre   spGrades is an open file
	         stuID, avrg, and grade have values to write
	   Post  Data written to file
*/
int writeStu  (FILE* spGrades, int  stuID,
               int   avrg,     char grade)
{
//	Statements
	fprintf(spGrades, "%04d %d %c\n",
	                   stuID, avrg, grade);
	return 0;
}	// writeStu