#include <stdio.h>
#include <time.h>
void findFridayThe13ths(int startYear, int endYear) {
for (int year = startYear; year <= endYear; ++year) {
for (int month = 1; month <= 12; month++) {
// Create a tm structure for the 13th day of the current month and year
struct tm timeStruct = {0};
timeStruct.tm_year = year - 1900; // tm_year is years since 1900
timeStruct.tm_mon = month - 1; // tm_mon is 0-based (0 = January)
timeStruct.tm_mday = 13; // 13th day of the month
// Normalize the tm structure to get the correct day of the week
mktime(&timeStruct);
// Check if the 13th is a Friday (tm_wday == 5)
if (timeStruct.tm_wday == 5) {
printf("Friday the 13th: %d-%02d-13\n", year, month);
}
}
}
}
int main() {
int startYear = 2025; // Starting year
int endYear = 2031; // Ending year
findFridayThe13ths(startYear, endYear);
return 0;
}
/*
run:
Friday the 13th: 2025-06-13
Friday the 13th: 2026-02-13
Friday the 13th: 2026-03-13
Friday the 13th: 2026-11-13
Friday the 13th: 2027-08-13
Friday the 13th: 2028-10-13
Friday the 13th: 2029-04-13
Friday the 13th: 2029-07-13
Friday the 13th: 2030-09-13
Friday the 13th: 2030-12-13
Friday the 13th: 2031-06-13
*/
