#include <stdio.h>
#include <time.h>
//
// ---------------------------------------------------------
// Function: daysUntilChristmas
// Purpose : Calculate how many days remain until Christmas.
// ---------------------------------------------------------
//
int daysUntilChristmas() {
// Get the current system time (seconds since 1970)
time_t now = time(NULL);
// Convert to a tm structure (local date/time)
struct tm today = *localtime(&now);
// Extract the current year (tm_year counts from 1900)
int year = today.tm_year + 1900;
// Build a tm structure for Christmas of the current year
struct tm christmas = {0};
christmas.tm_year = year - 1900; // Year since 1900
christmas.tm_mon = 11; // December (0-based index)
christmas.tm_mday = 25; // 25th day
// Convert Christmas date to time_t
time_t christmas_time = mktime(&christmas);
// If Christmas already passed this year, use next year
if (difftime(christmas_time, now) < 0) {
christmas.tm_year += 1; // Move to next year
christmas_time = mktime(&christmas);
}
// Calculate difference in seconds
double seconds = difftime(christmas_time, now);
// Convert seconds → days
int days = (int)(seconds / (60 * 60 * 24));
return days;
}
int main() {
int days = daysUntilChristmas();
printf("Days until Christmas: %d\n", days);
return 0;
}
/*
run:
Days until Christmas: 210
*/
