C language to achieve perpetual calendar effect

This article example Shared C language to achieve the specific code of perpetual calendar for your reference, the specific content is as follows

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define str "  SUN  MON TUE  WED  THU  FRI  SAT  "
 
void menu();     // The operating menu 
int leap(int year);    // Determine if a year is a leap year 
int days_month(int year, int month);    // Returns the number of days of a month 
int someday(int year, int month, int day);  // Calculate the day of the week 
void search_month(int year, int month);    // Output a calendar for that month 
void search_someday(int year, int month, int day);  // Check the day of the week 
 
int main()
{
 int i, year, month, day;
 int k1, k2, k3, k4;  // To determine whether the input data and operations are correct, 1 That's correct, 0 On behalf of the error 
 int a = 1;
 menu();
 do
 {
 printf(" Please enter the action you want to take (1-4):");
 scanf_s("%d", &i);
 getchar();
 switch (i)
 {
 case 1:
  printf(" Please enter the year you want to query: "); scanf_s("%d", &year);
  for (a; a <= 12; a++)
  {
  printf("\n\n---------*******  %d *******------------\n", a);
  search_month(year, a);
  }
  printf("---------*********************------------\n\n\n");
  break;
 
 
 case 2:
  printf(" Please enter the information you are looking for .\n");
  printf(" Year: "); scanf_s("%d", &year);
  printf(" Month: "); scanf_s("%d", &month);
  k1 = 1;
  while (k1)
  {
  if (month > 12 || month < 1)
  {
   printf(" The month you entered is wrong, please re-enter !\n");
   printf(" in :");
   scanf_s("%d", &month);
   if (month < 1 || month>12)  k1 = 1;
  }
  else k1 = 0;
  }
  search_month(year, month);
  printf("---------*********************------------\n\n\n");
  break;
 
 
 case 3:
  printf(" Please enter the date you want to query \n");
  printf(" Year: "); scanf_s("%d", &year);
  printf(" Month: "); scanf_s("%d", &month);
  k2 = 1;
  while (k2)
  {
  if (month > 12 || month < 1)
  {
   printf(" The month you entered is wrong, please re-enter !\n");
   printf(" in :");
   scanf_s("%d", &month);
   if (month < 1 || month>12)  k2 = 1;
  }
  else k2 = 0;
  }
  //  printf("%d years %d Month, %d day \n",year,month,days_month(year,month));    Debug to see if the date input is wrong, you can ignore 
  printf(" Date: "); scanf_s("%d", &day);
  k3 = 1;
  while (k3)
  {
  if (day > days_month(year, month) || day < 1)
  {
   printf(" The date you entered is wrong, please reenter it !\n");
   printf(" The date of :");
   scanf_s("%d", &day);
   if (day > days_month(year, month) || day < 1)  k3 = 1;
  }
  else k3 = 0;
  }
  search_someday(year, month, day);
  printf("---------*********************------------\n\n\n"); break;
 
 
 case 4:exit(0);
  printf("---------*********************------------\n\n\n"); break;
 
 
 default:
  k4 = 1;
  while (k4)
  {
  printf(" You entered the data is wrong, please re - enter your operation (1-4):");
  scanf_s("%d", &i);
  if (i < 1 || i>4)  k4 = 1;
  else k4 = 0;
  }
  break;
 }
 } while (i > 0 && i < 5);
 return 0;
}
 
void menu()
{
 int i = 1;
 printf("\n\n\t\t----------------------------------------\n");
 printf("\t\t|--------------------------------------|\n");
 printf("\t\t|      %d.  Output a calendar for a given year      |\n", i);
 printf("\t\t|      %d.  Output a calendar for that month      |\n", i + 1);
 printf("\t\t|      %d.  Check the day of the week     |\n", i + 2);
 printf("\t\t|      %d.  Log out         |\n", i + 3);
 printf("\t\t|--------------------------------------|\n");
 printf("\t\t----------------------------------------\n\n");
 
}
 
int leap(int year)
{
 if ((year % 4 == 0 && year % 100 != 0) || year % 400 == 0) return 1;
 else return 0;
}
 
int days_month(int year, int month)
{
 int days_month;
 switch (month)
 {
 case 1:
 case 3:
 case 5:
 case 7:
 case 8:
 case 10:
 case 12: days_month = 31; break;
 
 case 4:
 case 6:
 case 9:
 case 11:days_month = 30; break;
 
 case 2:
 if (leap(year) == 1)
 {
  days_month = 29; break;
 }
 else days_month = 28; break;
 }
 return days_month;
}
 
int someday(int year, int month, int day)
{
 // This function USES the special calculation formula, detailed can see  http://blog.163.com/hexin_mars_blog/blog/static/248215040201571351115699/
 int someday, m, n, i; //someday Indicates the day of the week of the query 
 m = year - year / 1000 * 1000;
 n = m - m / 100 * 100 - 1;      // Used to get the last two digits of the year 
 int days = 0;
 for (i = 1; i < month; i++) days = days + days_month(year, i);
 days = days + day;
 someday = (n + n / 4 - n / 100 + n / 400 + days) % 7;
 return someday;
}
 
void search_someday(int year, int month, int day)
{
 char weekname[20];
 switch (someday(year, month, day))
 {
 case 0:strcpy_s(weekname, " Sunday "); break;
 case 1:strcpy_s(weekname, " week 1"); break;
 case 2:strcpy_s(weekname, " week 2"); break;
 case 3:strcpy_s(weekname, " week 3"); break;
 case 4:strcpy_s(weekname, " week 4"); break;
 case 5:strcpy_s(weekname, " week 5"); break;
 case 6:strcpy_s(weekname, " week 6"); break;
 }
 printf(" The date you want to check is %s\n", weekname);
}
 
void search_month(int year, int month)
{
 int i = 0, j, k = 0, m;   //j Used to record the end of a month 1 What day of the week is it   m Used to record the number of days in a month  k Used for line breaks 
 char x[10] = "   ";
 m = days_month(year, month);
 j = someday(year, month, 1);
 
 // Output a calendar for that month 
 printf("------------------------------------------\n");
 printf("%s\n", str);
 for (; i < j; i++)
 {
 printf("%s", x); k++;
 }
 for (i = 1; i <= m; i++)
 {
 k++;
 if (k % 7 == 0)
 {
  if (i < 10)
  {
  printf("  %d ", i);
  printf("\n");
  }
  else if (i >= 10)
  {
  printf("  %d ", i);
  printf("\n");
  }
 }
 else
 {
  if (i < 10)
  {
  printf("  %d ", i);
  }
  else if (i >= 10)
  {
  printf("  %d ", i);
  }
 }
 }
 printf("\n------------------------------------------\n");
}
 
void exit()
{
 exit(0);
}