A calendar displays the days of each month according to the starting day of the year. In C++, we can generate a calendar for any given year by calculating the first day of the year and the number of days in each month.
- The program handles both leap years and non-leap years.
- It prints all 12 months with days arranged according to their weekdays.
- The calendar is generated without using any built-in calendar library.
Approach
The calendar is generated in three main steps:
- Calculate the day of the week for January 1 of the given year.
- Determine the number of days in each month, including February for leap years.
- Print each month's days in the correct weekday positions.
Example: For 2016, the program prints the complete calendar for the year. Since 2016 is a leap year, February contains 29 days.
#include<bits/stdc++.h>
using namespace std;
/*A Function that returns the index of the day
of the date- day/month/year
For e.g-
Index Day
0 Sunday
1 Monday
2 Tuesday
3 Wednesday
4 Thursday
5 Friday
6 Saturday*/
int dayNumber(int day, int month, int year)
{
static int t[] = { 0, 3, 2, 5, 0, 3, 5, 1,
4, 6, 2, 4 };
year -= month < 3;
return ( year + year/4 - year/100 +
year/400 + t[month-1] + day) % 7;
}
/*
A Function that returns the name of the month
with a given month number
Month Number Name
0 January
1 February
2 March
3 April
4 May
5 June
6 July
7 August
8 September
9 October
10 November
11 December */
string getMonthName(int monthNumber)
{
string months[] = {"January", "February", "March",
"April", "May", "June",
"July", "August", "September",
"October", "November", "December"
};
return (months[monthNumber]);
}
/* A Function to return the number of days in
a month
Month Number Name Number of Days
0 January 31
1 February 28 (non-leap) / 29 (leap)
2 March 31
3 April 30
4 May 31
5 June 30
6 July 31
7 August 31
8 September 30
9 October 31
10 November 30
11 December 31
*/
int numberOfDays (int monthNumber, int year)
{
// January
if (monthNumber == 0)
return (31);
// February
if (monthNumber == 1)
{
// If the year is leap then February has
// 29 days
if (year % 400 == 0 ||
(year % 4 == 0 && year % 100 != 0))
return (29);
else
return (28);
}
// March
if (monthNumber == 2)
return (31);
// April
if (monthNumber == 3)
return (30);
// May
if (monthNumber == 4)
return (31);
// June
if (monthNumber == 5)
return (30);
// July
if (monthNumber == 6)
return (31);
// August
if (monthNumber == 7)
return (31);
// September
if (monthNumber == 8)
return (30);
// October
if (monthNumber == 9)
return (31);
// November
if (monthNumber == 10)
return (30);
// December
if (monthNumber == 11)
return (31);
}
// Function to print the calendar of the given year
void printCalendar(int year)
{
printf (" Calendar - %d\n\n", year);
int days;
// Index of the day from 0 to 6
int current = dayNumber (1, 1, year);
// i --> Iterate through all the months
// j --> Iterate through all the days of the
// month - i
for (int i = 0; i < 12; i++)
{
days = numberOfDays (i, year);
// Print the current month name
printf("\n ------------%s-------------\n",
getMonthName (i).c_str());
// Print the columns
printf(" Sun Mon Tue Wed Thu Fri Sat\n");
// Print appropriate spaces
int k;
for (k = 0; k < current; k++)
printf(" ");
for (int j = 1; j <= days; j++)
{
printf("%5d", j);
if (++k > 6)
{
k = 0;
printf("\n");
}
}
if (k)
printf("\n");
current = k;
}
return;
}
// Driver Program to check above functions
int main()
{
int year = 2016;
printCalendar(year);
return (0);
}
Output
Calendar - 2016
------------January-------------
Sun Mon Tue Wed Thu Fri Sat
1 2
3 4 5 6 7 8 9
10 11 12 13 14 15 16
17 18 19 20 21 22 23
24 25 26 27 28 29 30
31
------------February-------------
Sun Mon Tue Wed Thu Fri Sat
1 2 3 4 5 6
7 8 9 10 11 12 13
14 15 16 17 18 19 20
21 22 23 24 25 26 27
28 29
------------March-------------
Sun Mon Tue Wed Thu Fri Sat
1 2 3 4 5
6 7 8 9 10 11 12
13 14 15 16 17 18 19
20 21 22 23 24 25 26
27 28 29 30 31
------------April-------------
Sun Mon Tue Wed Thu Fri Sat
1 2
3 4 5 6 7 8 9
10 11 12 13 14 15 16
17 18 19 20 21 22 23
24 25 26 27 28 29 30
------------May-------------
Sun Mon Tue Wed Thu Fri Sat
1 2 3 4 5 6 7
8 9 10 11 12 13 14
15 16 17 18 19 20 21
22 23 24 25 26 27 28
29 30 31
------------June-------------
Sun Mon Tue Wed Thu Fri Sat
1 2 3 4
5 6 7 8 9 10 11
12 13 14 15 16 17 18
19 20 21 22 23 24 25
26 27 28 29 30
------------July-------------
Sun Mon Tue Wed Thu Fri Sat
1 2
3 4 5 6 7 8 9
10 11 12 13 14 15 16
17 18 19 20 21 22 23
24 25 26 27 28 29 30
31
------------August-------------
Sun Mon Tue Wed Thu Fri Sat
1 2 3 4 5 6
7 8 9 10 11 12 13
14 15 16 17 18 19 20
21 22 23 24 25 26 27
28 29 30 31
------------September-------------
Sun Mon Tue Wed Thu Fri Sat
1 2 3
4 5 6 7 8 9 10
11 12 13 14 15 16 17
18 19 20 21 22 23 24
25 26 27 28 29 30
------------October-------------
Sun Mon Tue Wed Thu Fri Sat
1
2 3 4 5 6 7 8
9 10 11 12 13 14 15
16 17 18 19 20 21 22
23 24 25 26 27 28 29
30 31
------------November-------------
Sun Mon Tue Wed Thu Fri Sat
1 2 3 4 5
6 7 8 9 10 11 12
13 14 15 16 17 18 19
20 21 22 23 24 25 26
27 28 29 30
------------December-------------
Sun Mon Tue Wed Thu Fri Sat
1 2 3
4 5 6 7 8 9 10
11 12 13 14 15 16 17
18 19 20 21 22 23 24
25 26 27 28 29 30 31
Sure. Since you’re keeping the
original code
, the explanation should match its exact functions and flow.
Explanation
- dayNumber() calculates the weekday index for the first day of the year using a calendar formula.
- getMonthName() returns the name of a month based on its index from 0 to 11.
- numberOfDays() returns the number of days in each month and checks the leap-year condition for February.
- printCalendar() iterates through all 12 months, aligns the first day using spaces, and prints the dates under the correct weekdays.
- main() sets the year to 2016 and calls printCalendar() to display its calendar.