//Name: Christine 
//Purpose: The purpose of the program is to save all records. If the inputted
//         data finds a duplicate ID's, it will automatically save to
//         myfile2.dat.

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

struct record
{
  int  studnumb;
  char studname[30];
};
typedef record stud_rec;
// CLEAR FILE
void clrfile() {
  FILE *fptr;
  //
  clrscr();
  fptr = fopen("myfile.dat", "w");
  if (fptr != NULL) {
    fclose(fptr);
    printf("File has been cleared. \n");
  }
  else
    printf("Error in creating the file. \n");
  getch();
}
// FILE ENTRY
void add_rec() {
  stud_rec stud, temp;
  char ans;
  FILE *fptr;
  FILE *fptr_trash;
  int max_rec, rec_num = 0;
  int duplicate = 0;
  //
  clrscr();
  printf("Record Entry \n");
  do {
    printf("Stud ID# : ");
    scanf("%d", &stud.studnumb);
  } while (stud.studnumb < 1000 || stud.studnumb > 9999);
  fflush(stdin);
  do {
    printf("Stud Name: ");
    gets(stud.studname);
  } while (strlen(stud.studname) == 0 || strlen(stud.studname) > 29);
  //
  fptr  = fopen("myfile.dat", "a+");
  if (fptr != NULL) {
    fseek(fptr, (long) 0, SEEK_END);
    max_rec = ftell(fptr) / sizeof(record);
    if (max_rec > 0)
      rewind(fptr);
      while (rec_num < max_rec) {
	fread(&temp, sizeof(record), 1, fptr);
	if (stud.studnumb == temp.studnumb) {
	  duplicate = 1;
	  break;
	}
	rec_num++;
      }
      if (!duplicate) {
	rewind(fptr);
	fwrite(&stud, sizeof(record), 1, fptr);
	printf("Record has been added to file. \n");
	fclose(fptr);
      }else {
	fptr_trash = fopen("myfile2.dat", "a+");
	fwrite(&stud, sizeof(record), 1, fptr_trash);
	printf("Invalid ID. Sent to myfile2.dat\n");
	fclose(fptr_trash);
      }

  }
  else
    printf("Error in opening the file. \n");
  getch();
}
// DISPLAY ALL RECORDS
void readrec() {
  stud_rec stud;
  char ans;
  long a = 0;
  FILE *fptr;
  int rec_num = 0, max_rec;
  //
  fptr = fopen("myfile.dat", "r");
  if (fptr != NULL) {
    fseek(fptr, a, SEEK_END);
    max_rec = ftell(fptr) / sizeof(record);
    if (max_rec > 0) {
      rewind(fptr);
      while (rec_num < max_rec) {
	fread(&stud, sizeof(record), 1, fptr);
	printf("Stud ID# : %d \n", stud.studnumb);
	printf("Stud Name: %s \n", stud.studname);
	printf("\n");
	rec_num++;
      }
      printf("End of file. \n");
      fclose(fptr);
    }
    else
      printf("File is empty. \n");
  }
  else
    printf("Error in opening file. \n");
  getch();
}
// DISPLAY nTH RECORD
void readnth(int n) {
  stud_rec stud;
  FILE *fptr;
  int max_rec;
  //
  fptr = fopen("myfile.dat", "r");
  if (fptr != NULL) {
    rewind(fptr);
    fseek(fptr, (long) 0, SEEK_END);
    max_rec = ftell(fptr) / sizeof(record);
    if (max_rec >= n) {
      rewind(fptr);
      fseek(fptr, (long) (n-1)*sizeof(record), SEEK_SET);
      fread(&stud, sizeof(record), 1, fptr);
      printf("Stud ID# : %d \n", stud.studnumb);
      printf("Stud Name: %s \n", stud.studname);
      printf("\n");
      fclose(fptr);
    }
    else
      printf("Record # %d not existing. \n", n);
  }
  else
    printf("Error in opening file. \n");
  getch();
}
void main() {
  textmode(2);
  char ans;
  int  n;
  do {
    clrscr();
    printf("1. Record Entry                  \n");
    printf("2. Display All Records           \n");
    printf("3. Display nth Record            \n");
    printf("9. Clear File                    \n");
    printf("---------------------------------\n");
    printf("0. Exit  (or ESC)                \n");
    //
    ans = getch();
    switch(ans) {
      case '1' :
	clrscr();
	add_rec();
	break;
      case '2' :
	clrscr();
	readrec();
	break;
      case '3' :
	clrscr();
	do {
	  printf("Enter Record#: ");
	  scanf("%d", &n);
	} while (n < 1);
	readnth(n);
	break;
      case '9' :
	clrscr();
	clrfile();
	break;
    }
  } while (ans != 27 && ans != '0');
}