Make or print calendar for any year

This program will make and print a calendar for any year starting from 1800 AD. However 1800 is not a fixed starting point, you can tweak the code and change firstYear, dayOffset and firstLeapYear to get any starting point. The dayoffset is the first day of our start year which may not be a Sunday ( in 1800 it was Wednesday). The logic goes like that it first calculates the number of days passed from a starting point (1800 AD). The days passed is then divided by 7 to get the starting day for a particular month. Then it gets the number of days in that month and loops accordingly to print the number of days. The example here prints the calendar for 2009. Just change the year variable in main function to print calendar of that particular year.

#include

int IsLeapYear(int Year)

{

    if (Year % 400 == 0 || (Year % 4 == 0 && Year % 100 != 0))

        return 1;

    return 0;

}

int DaysPassedFromYear(int firstYear, int month,int year)

{

    int days;

    int daysPassed[] = { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334}; //per month per year

    const int dayOffset = 3; //The first day of our start year may not be a Sunday ( in 1800 it was Wednesday)

    const int firstLeapYear = 1804; //help to reduce how many leap years we have to check

    int count;



    //calculates basic number of days passed 

    days = (year - firstYear) * 365;

    days += dayOffset;

    days += daysPassed[month-1];

    

    //add on the extra leapdays for past years

    for (count = firstLeapYear; count < year ; count +=4)

    {

        if (IsLeapYear(count) )

        {

            days++;

        }

    }



    //add leapday for this year if requested  month is greater than  Feb  

    if( month > 2 && IsLeapYear(year) )

    {

        days++;

    }



    return days;



}



int GetNumberOfDaysInMonth(int Month,int Year)

{

    int NumberOfDaysInMonth;

    printf("\n");

    switch (Month)

    {

        case 1:

            printf("              January %d\n",Year);

            NumberOfDaysInMonth = 31;

            break;

        case 2:

            printf("              February %d\n",Year);

            if(IsLeapYear(Year))

                NumberOfDaysInMonth = 29;

            else

                NumberOfDaysInMonth = 28;

            break;

        case 3:

            printf("               March %d\n",Year);

            NumberOfDaysInMonth = 31;

            break;

        case 4:

            printf("               April %d\n",Year);

            NumberOfDaysInMonth = 30;

            break;

        case 5:

            printf("                May %d\n",Year);

            NumberOfDaysInMonth = 31;

            break;

        case 6:

            printf("                June %d\n",Year);

            NumberOfDaysInMonth = 30;

            break;

        case 7:

            printf("                July %d\n",Year);

            NumberOfDaysInMonth = 31;

            break;

        case 8:

            printf("              August %d\n",Year);

            NumberOfDaysInMonth = 31;

            break;

        case 9:

            printf("              September %d\n",Year);

            NumberOfDaysInMonth = 30;

            break;

        case 10:

            printf("              October %d\n",Year);

            NumberOfDaysInMonth = 31;

            break;

        case 11:

            printf("              November %d\n",Year);

            NumberOfDaysInMonth = 30;

            break;

        case 12:

            printf("              December %d\n",Year);

            NumberOfDaysInMonth = 31;

            break;

    }

    printf("__________________________________________");

    printf("\n  Sun   Mon   Tue   Wed   Thu   Fri   Sat\n\n");

    return NumberOfDaysInMonth;

}



int main()

{

    int year=2009;

    int month;

    

    for(month=1;month<=12;month++)

    {

        const int firstYear = 1800; //This is our start point

        int NumDaysInMonth=GetNumberOfDaysInMonth(month,year);

        int firstDayOfMonth = DaysPassedFromYear(firstYear,month,year) % 7;//0-Sunday 1-Monday

        firstDayOfMonth++;//offsetting so that 1-Sunday,2-monday etc

        int i;

        for(i=1;i        {

            printf("      ");

            if(i%7 == 0) printf("\n");

        }

        for(i=firstDayOfMonth;i        {

            if((i-firstDayOfMonth) < 9)

                printf("   %d  ",i-firstDayOfMonth+1);

            else

                printf("   %d ",i-firstDayOfMonth+1);

            if(i%7 == 0) printf("\n");

        }

        printf("\n");

    }

    return 0;

}

compiled on:gcc and linux
output: