C program to display month by month calendar for a given year

Prerequisite: Find day of the week for a given date Given a year N, the task is to print the calendar for every month of the given year. Implementation:

C

// C program to print the month by month
// calendar for the given year

#include <stdio.h>

// Function that returns the index of the
// day for date DD/MM/YYYY
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;
}

// Function that returns the name of the
// month for the given month Number
// January - 0, February - 1 and so on
char* getMonthName(int monthNumber)
{
    char* month;

    switch (monthNumber) {
    case 0:
        month = "January";
        break;
    case 1:
        month = "February";
        break;
    case 2:
        month = "March";
        break;
    case 3:
        month = "April";
        break;
    case 4:
        month = "May";
        break;
    case 5:
        month = "June";
        break;
    case 6:
        month = "July";
        break;
    case 7:
        month = "August";
        break;
    case 8:
        month = "September";
        break;
    case 9:
        month = "October";
        break;
    case 10:
        month = "November";
        break;
    case 11:
        month = "December";
        break;
    }
    return month;
}

// Function to return the number of days
// in a month
int numberOfDays(int monthNumber, int year)
{
    // January
    if (monthNumber == 0)
        return (31);

    // February
    if (monthNumber == 1) {
        // If the year is leap then Feb
        // 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 for Iterate through months
    // j for Iterate through 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));

        // 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 Code
int main()
{
    int year = 2016;

    // Function Call
    printCalendar(year);
    return 0;
}

Output

...  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

Time Complexity: O(1)
Auxiliary Space: O(1), As constant extra space is used.