#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
/* qsort C-string comparison function from qsort(3) man-page */
static int
cmpstringp(const void *p1, const void *p2)
{
  /* The actual arguments to this function are "pointers to
     pointers to char", but strcmp(3) arguments are "pointers
     to char", hence the following cast plus dereference */
 
  return strcmp(* (char * const *) p1, * (char * const *) p2);
}
 
static double
get_score(int scores) {
  size_t sum = 0, nscores = 0;
  for ( ; scores > 0; scores /= 10) {
    sum += scores % 10;
    ++nscores;
  }
  return (double)sum / nscores; /*XXX remove /nscore to get mere sum */
}
 
int main(void) {
  const char* student_list[] = {
    /* группа | фио |  оценки */
    "4272 Галкин Г. А. 5445",
    "4273 Константинопольский А. А. 4333",
    "4273 Курочкин А. А. 3433",
    "4272 Козлов И. И. 4443"
  };
  const size_t n = sizeof(student_list) / sizeof(student_list[0]);
  const char* *pstudent = NULL;
  int last_group = -1;
  double group_score = 0;
  size_t group_count = 0;
 
  qsort(student_list, n, sizeof(student_list[0]), cmpstringp);
 
  for (pstudent = student_list; pstudent != &student_list[n]; ++pstudent) {
    int group = -1, scores = -1;
    char *name = NULL;
 
    errno = 0;
    if (sscanf(*pstudent, "%d %m[^0-9] %d", &group, &name, &scores) != 3) {
      if (errno) perror("sscanf");
      fprintf(stderr, "error: can't parse '%s'\n", *pstudent);
      exit(EXIT_FAILURE);
    }
    if (group != last_group) {
      if (group_count > 0) /* print the last group average score */
        printf("%d %f\n", last_group, (double)group_score/group_count);
 
      group_score = 0; /* start new group */
      group_count = 0;
      last_group = group;
    }
    ++group_count;
    group_score += get_score(scores);
    free(name);
  }
  if (group_count > 0) /* print the last group average score */
    printf("%d %f\n", last_group, (double)group_score/group_count);
  return 0;
}
 

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