Question

I’m trying to complete a lab in which I have to calculate the total Grade Point Average (GPA) from course information given in a linked list of structures. I’m trying to define each letter grade with its appropriate grade point (‘A’ = 4.0, “A-” = 3.7 …). The course grades are stored in arrays of chars. I’m able to use the #define derivative to define the letter grades A,B,C,D,E, but I am having trouble defining the +/- grades. Is using the #define derivative the proper way to achieve this task? and if so, would someone be able to show me the proper syntax.

/* Definition of a data node holding course information */
  struct course {
    int term;
    char name[15];
    char abbrev[20];
    float hours;
    char grade [4];
    char type[12];
    struct course *next;
  };



float gpa ( struct course *ptr )
{
  float totalhours;
  float gpa;
  float gradepoints;

  while (ptr != NULL )
    {
      totalhours += (ptr->hours);
      gradepoints = (ptr->hours * ptr->grade);
    }
  gpa = (gradepoints / totalhours);
}

Answer 1

What you are looking for is a map, or a dictionary, which is not natively supported in C. You can implement a simple map for your use case as an array of structs as such:

struct GradeInfo {
  char *grade;
  float value;
};
struct GradeInfo GRADES[] = { {"A", 4.0}, {"A-", 3.7}, ..., {NULL, 0.0}};

Then loop over this array inside your for loop (fixing a few more bugs):

float gpa ( struct course *ptr )
{
  float totalhours = 0.0;
  float gradepoints = 0.0;

  for (; ptr; ptr = ptr->next)
    {
      float grade = -1.0;
      struct GradeInfo *info;
      for (info = GRADES; info->grade; ++info) {
        if (!strcmp(ptr->grade, info->grade)) {
          grade = info->value;
          break;
        }
      }
      if (grade < 0) {
        continue;
      }
      totalhours += (ptr->hours);
      gradepoints = (ptr->hours * ptr->grade);
    }
  if (!totalhours) {
    return 0.0;
  }
  return (gradepoints / totalhours);
}