/* Sample Solution to Assignment #2 */

#include <string.h>
#include <stdio.h>
#include <stdlib.h>

#define MAX_STUDENTS 25      /* Maximum number of students enrolled */
#define MAX_COURSE_NUM 5     /* Maximum number of courses a student can take*/
#define TOTAL_COURSES 7      /* Number of courses offered */ 

struct course {
  int num;       /* unique course number */
  int credits;   /* number of credits per course */
};

struct student{
  int num;                      /* student number */
  int courses[MAX_COURSE_NUM];  /* course numbers of courses taken */
  char grades[MAX_COURSE_NUM];  /* student grade in each course above */
  int courses_taken;            /* actual number of courses being taken */
  float GPA;                    /* grade point average */
};

/* courses offered at Llenroc */
struct course courses_offered[TOTAL_COURSES] = 
{{100, 4}, {113, 1}, {212, 4}, {213, 2}, {611, 6}, {709, 1}, {990, 8}};

/* Error function.  Print out the error message argument and terminate 
   program execution.  The exit function terminates the program with the
   argument (in this case, 1 - I'm using a non-zero value because calling
   fail indicates non-standard termination.  exit is found in <stdio.h> */

void fail(char *error_message)
{
  printf("\n");
  printf("%s",error_message);
  printf("\n");
  exit(1);
}

/* Fail if the argument is not a valid grade */
void check_grade(char g)
{
  switch(g){
  case 'A': case 'B': case 'C': case 'D': case 'F':
    break;
  default:
    printf("%c\n", g);
    fail("Illegal Grade");
  }
  return;
}

/* Fail if the course_num argument is not on the list of courses offered */
void check_course(int course_num)
{
  int i;

  for (i=0; i< TOTAL_COURSES; i++){
    if (courses_offered[i].num == course_num)
      return;
  }

  fail("Illegal Course Number");
  return;
}

/* Scan in student information other than the GPA */
void scan_student(struct student *s)
{
  int i;

  printf("Student number:");
  scanf("%d",&(s->num));

  /* Get number of courses taken, checking against maximum of MAX_COURSE_NUM */
  printf("Number of Courses taken(Maximum %d): ", MAX_COURSE_NUM);
  scanf("%d",&s->courses_taken);
  if (s->courses_taken > MAX_COURSE_NUM)
    fail("Max number of courses exceeded");

  /* Scan in courses and grades */
  for (i =0; i < s->courses_taken; i++){
    printf("Course: ");
    scanf("%d", &(s->courses[i]));
    check_course(s->courses[i]);

    printf("Grade: ");
    scanf("%1s", &(s->grades[i]));
    check_grade(s->grades[i]);
  }

  return;
}
  
/* Print out student information */
void print_student(struct student s)
{
  int i;

  printf("Student number: %d\n", s.num);

  for(i=0; i<s.courses_taken; i++){
    printf("%d:%c  ", s.courses[i], s.grades[i]);
  }

  printf("\n");
  printf("%.2f\n", s.GPA);
  return;
}

/* Return the number of credits for the course with the given number */
int get_credits(int course_num)
{
  int i;

  for (i=0; i<TOTAL_COURSES; i++){
    if (courses_offered[i].num == course_num)
      return courses_offered[i].credits;
  }

  fail("get_credits: course not found");
  return -1;
}

/* Translate a letter grade into the corresponding numeric value */
float translate_grade(char g)
{
  float result;

  switch(g) {
  case 'A':
    result = 4.0;
    break;
  case 'B':
    result = 3.0;
    break;
  case 'C':
    result = 2.0;
    break;
  case 'D':
    result = 1.0;
    break;
  case 'F':
    result = 0.0;
    break;
  default:
    fail("translate_grade: illegal grade");
    break;
  }

  return result;
}

/* Calculate a student's gpa */
float gpa(struct student s)
{
  int i;                    /* loop counter */
  int credits;              /* credits for current course */
  float translated_grade;   /* numeric grade for current course */
  int total_credits = 0;    /* sum of all credit hours */
  float sum = 0.0;          /* sum of all grade points */

  /* For each course the student is taking, 
     calculate the credit hours and numeric grade, adding each
     to the totals 
   */
  for (i=0; i<s.courses_taken; i++){
    credits = get_credits(s.courses[i]);
    translated_grade = translate_grade(s.grades[i]);
    sum += credits * translated_grade;
    total_credits += credits;
  }
  
  return sum/total_credits;
}

/******************************************/
/*    Sorting and Associated functions    */
/******************************************/

/* copy information in student s2 into s1 */
void copy_student(struct student *s1, struct student s2)
{
  int i;

  s1->num = s2.num;
  
  for (i=0;i<s2.courses_taken; i++){
    s1->courses[i] = s2.courses[i];
    s1->grades[i] = s2.grades[i];
  }

  s1->courses_taken = s2.courses_taken;
  s1->GPA = s2.GPA;

  return;
}

/* swap the values in structure pointed to by s1 in structure pointed
   to by s2
 */
void swap(struct student *s1, struct student *s2)
{
  struct student temp;

  copy_student(&temp, *s1);
  copy_student(s1, *s2);
  copy_student(s2, temp);

  return;
}

/* insert the array element at index into sorted section of array
   ranging from 0 to index-1.  Array sorted in non-increasing order by GPA
 */
void insert(struct student students[], int index)
{
  int i;

  for (i=index; i> 0; i--){
    if (students[i-1].GPA < students[i].GPA)
      swap(&students[i-1], &students[i]);
    else
      break;
  }

  return;
}

/* Sort array students of given length in non-increasing order by GPA */
void isort(struct student students[], int length)
{
  int i;

  for (i=1; i< length; i++)
    insert(students, i);

  return;
}

/* Read in students.
   Calculate GPA.
   Sort students by GPA.
   Print out students.
 */
int main(void)
{
  int i;
  struct student students[MAX_STUDENTS];
  int number_of_students;

  /* Scan in number of students */
  printf("How many students are there?\n");
  scanf("%d", &number_of_students);
  
  /* Error checking: */
  if (number_of_students <= 0)
    fail("No students?");
  if (number_of_students > MAX_STUDENTS)
    fail("Too many students");

  for (i=0; i<number_of_students; i++){
    scan_student(&students[i]);
    students[i].GPA = gpa(students[i]);  /* Calculate student GPA */
  }

  /* Sort Students by GPA */
  isort(students, number_of_students);

  /* Print Students */
  printf("\n");
  for (i=0; i<number_of_students; i++){
    print_student(students[i]);
  }

  return 0;
}