luc018.c (1220B)
1 /* According to Gregorian calender, it was Monday on the date 01/01/01. 2 if any year is input through the keyboard write a program to find out 3 what is the day on 1st January of this year. */ 4 /* Let Us C, Chap- 3, Page - 53, Qn No.: f(i) */ 5 6 #include <stdio.h> 7 8 int is_leap(int year) { 9 if ((year % 400 == 0) || (year % 4 == 0 && year % 100 != 0)) { 10 return 1; 11 } 12 return 0; 13 } 14 15 int main() { 16 long long year; // long long for year input if years far in the future/past are tested 17 int i; 18 long long total_days = 0; 19 int day_index; 20 21 // Day names array for output 22 const char *day_names[] = {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"}; 23 24 printf("Enter the year (e.g., 2025): "); 25 if (scanf("%lld", &year) != 1 || year < 1) { 26 printf("Invalid year input. Please enter a positive integer year (>= 1).\n"); 27 return 1; 28 } 29 int years_passed = year - 1; 30 long long leap_years = years_passed / 4 - years_passed / 100 + years_passed / 400; 31 total_days = years_passed * 365 + leap_years; 32 day_index = (total_days + 1) % 7; 33 printf("\nOn January 1st, %lld, the day was: %s.\n", year, day_names[day_index]); 34 return 0; 35 }