Courses

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

//ex 1
struct Course{
  char name[51];
  char date[11];
  int lectures;
  float price;
};

int main() {
    FILE *file;

    file = fopen("Course.bin", "rb");
    if (file == NULL) {
      printf("File could not be opened\n");
      return 1;
    }
                            // Четем първо броя на курсовете който е посочен в първия ред на файла
    if(fseek(file, 0, SEEK_END) != 0){               //int n;
      printf("File could not be seeked\n");          //if (fread(&n, sizeof(int), 1, file) != 1) {
      fclose(file);                                  //printf("Could not read number of courses\n");
      return 1;                                      //fclose(file);
    }                                                //return 1;
                                                     //}
    long size = ftell(file);
    if(size < 0){                                    // За side safety: проверка дали броят е положителен
      printf("Error determining to end of file\n");
      fclose(file);                                  //if (n <= 0) {
      return 1;                                      //printf("Invalid number of courses in file\n");
    }                                                //fclose(file);
                                                     //return 1;
    rewind(file);                                    //}

    int n = size / sizeof(struct Course);
    ////////////////////////////////////////////////
    struct Course* courses = (struct Course*) malloc(n * sizeof(struct Course));

    if (courses == NULL) {
      printf("Memory could not be allocated\n");
      fclose(file);
      return 1;
    }

    if(fread(courses, sizeof(struct Course), n, file) != n) {
      if (feof(file)) {
        perror("");        //printf("File could not be read\n");
      }
      else if (ferror(file)) {
        perror("");       //printf("Error reading file\n");
      }
      free(courses);
      fclose(file);
      return 1;
    }
    fclose(file);
    free(courses);

    return 0;
}

//ex 2

int discount(struct Course* courses, int n, int index){

  if (index < 0 || index >= n) {
    printf("Invalid index\n");
    return 1;
  }

  courses[index].price *= 0.9;

  printf("%.2flv - %s - %s\n", courses[index].price, courses[index].name, courses[index].date);

  return 0;
}

//ex 3
int write (struct Course* courses, int n, float max, float min){

  FILE *file;
  file = fopen("offer.txt", "w");
  if (file == NULL) {
    printf("File could not be opened\n");
    return 1;
  }

  int counter = 0;
  for (int i = 0; i < n; i++) {
    if (courses[i].price <= max && courses[i].price >= min) {
      counter++;
      fprintf("%s\n%s\n%d\n%.2flv", courses[i].name, courses[i].date, courses[i].lectures, courses[i].price);
    }
  }
  fclose(file);
  return counter;
}

//ex4
struct Course* deleteCourse(struct Course* courses, int* n, const char name[51], const char date[11]) {

  int index = -1;

  for (int i = 0; i < *n; i++) {
    if (strcmp(courses[i].name, name) == 0 && strcmp(courses[i].date, date) == 0) {
      index = i;
      break;
    }
  }

  if (index == -1) {
    printf("Course not found.\n");
    return courses;  // няма нужда от промяна
  }

  // изместване на елементите наляво
  for (int i = index; i < *n - 1; i++) {
    courses[i] = courses[i + 1];
  }

  // преоразмеряване на масива
  struct Course* resized = realloc(courses, (*n - 1) * sizeof(struct Course));
  if (resized == NULL && *n - 1 > 0) {
    perror("");
    return NULL;
  }

  (*n)--;  // намаляваме броя на елементите
  return resized;
}