Klavyeden gireceginiz iki tarih arasindaki günleri hesaplamak...

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

• typedef enum {FALSE, TRUE} BOOL;

• #define YEARBASE 1900

• typedef struct DATE_{//structure tanimi.Bu bizim sanki bi sinifimiz varmis gibi düsünün ve içindeki elemanlari kolayca tanir
  int day;
  int month;
  int year;
  }DATE;

• BOOL is_leap(int year);//return 0 veya 1 dir
  DATE *set_date(int day, int month, int year, DATE *date);
  void print_date(const DATE *date);
  long date_to_number(const DATE *date);
  int day_of_year(const DATE *date);
  long date_dif(const DATE *date1, const DATE *date2);
  BOOL is_valid(const DATE *date);

• char *days[] = {"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"};
  char *months[] = {"Jan", "Feb", "Mar", "Apr", "May", "Jun",
  "Jul","Aug", "Sep", "Oct", "Nov", "Dec"};

• int daytab[] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};//aylarin içindeki günlerin sayisi

• int main(void)
  {
  int day, month, year;
  DATE d1, d2;//DATE structure da tanimlanmisti d1 ilk girdigimiz tarihi tutuyor ,d2 ikinci girdigimiz tarihi tutuyor

• for (;;) {
  printf("first date [day()gün ,month(ay) ,year(yil)]: ");
  scanf("%d%d%d", &day, &month, &year);
  set_date(day, month, year, &d1);//
  if (!is_valid(&d1))//tarih kaliba uygunmu kontroluü
  printf("invalid date!\n");
  else
  break;
  }

• for (;;) {
  printf("second date [day()gün ,month(ay) ,year(yil)]: ");
  scanf("%d%d%d", &day, &month, &year);
  set_date(day, month, year, &d2);
  if (!is_valid(&d2))
  printf("invalid date!\n");
  else
  break;
  };

• printf("toplam gün sayisi ");
  print_date(&d1);//
  printf(" ve");
  print_date(&d2);
  printf(": %d\n", date_dif(&d1, &d2));
  return 0;
  }
  /*************************************************/
  BOOL is_leap(int year)
  {
  return (year % 4 == 0 && year % 100 != 0 || year % 400 == 0);
  }
  /*************************************************/
  DATE *set_date(int day, int month, int year, DATE *date)//structure da gün ay ce yilin yerlerini belirliyoruz
  {
  date->day = day;//-> yerine nokta da kullanabliriz.örnek date.day=day;
  date->month = month;
  date->year = year;
  return date;
  }

• /*************************************************/
  void print_date(const DATE *date)//ana fonksiyonda gönderdigimiz print date fonksiyonu
  {
  printf("%02d", date->day);

• switch (date->day) {
  case 1: case 21: case 31:
  printf("st "); break;
  case 2: case 22:
  printf("nd "); break;
  case 3: case 23:
  printf("rd "); break;
  default :
  printf("th ");
  }
  printf("%s ", months[date->month - 1]);
  printf("%d ", date->year);
  printf("%s", days[(int)(date_to_number(date) % 7)]);
  }
  /*************************************************/
  long date_to_number(const DATE *date)
  {
  long result = 0;
  int year;

• for (year = YEARBASE; year < date->year; year++)
  result += 365 + is_leap(year);
  result += day_of_year(date);
  return result;
  }
  /*************************************************/
  int day_of_year(const DATE *date)//ayin güne dönüsümünü yaptigi fonksiyon
  {
  int k;
  int result = date->day;

• daytab[1] = 28 + is_leap(date->year);

• for (k = 0; k < date->month - 1; ++k)
  result += daytab[k];
  return result;
  }
  /*************************************************/
  long date_dif(const DATE *date1, const DATE *date2)
  {
  return date_to_number(date1) - date_to_number(date2);
  }
  /*************************************************/
  BOOL is_valid(const DATE *date)//girdigimiz tarih kaliba uygunmu kontrol yeri
  {
  daytab[1] = 28 + is_leap(date->year);

• if (date->year < YEARBASE)
  return FALSE;
  if (date->day > daytab[date->month - 1] || date->day <= 0)
  return FALSE;
  if (date->month < 1 || date->month > 12)
  return FALSE;

• return TRUE;
  }