/*
 * File: calendar.c
 * ----------------
 * This program is used to generate a calendar for a year
 * entered by the user.
 */

#include <stdio.h>

/* 
 * Constants:
 * ----------
 * Days of the week are represented by the integers 0-6.
 * Months of the year are identified by the integers 1-12;
 * because this numeric representation for months is in
 * common use, no special constants are defined.
 */

#define SUNDAY     0
#define MONDAY     1
#define TUESDAY    2
#define WEDNESDAY  3
#define THURSDAY   4
#define FRIDAY     5
#define SATURDAY   6

/* Function prototypes */

void GiveInstructions(void);
int GetYearFromUser(void);
void PrintCalendar(int year);
void PrintCalendarMonth(int month, int year);
int FirstDayOfMonth(int month, int year);
char * MonthName(int month);

You need to put function prototypes that are missing here.

/* Main program */

int main(void)
{
    int year;

    GiveInstructions();
    year = GetYearFromUser();
    PrintCalendar(year);

    return 0;
}

/*
 * Function: GiveInstructions
 * Usage: GiveInstructions();
 * --------------------------
 * This procedure prints out instructions to the user.
 */

void GiveInstructions(void)
{
    printf("This program displays a calendar for a full\n");
    printf("year.  Any year after 1899 is okay.\n");
}

/*
 * Function: GetYearFromUser
 * Usage: year = GetYearFromUser();
 * --------------------------------
 * This function reads in a year from the user and returns
 * that value.  If the user enters a year before 1900, the
 * function gives the user another chance. Using a while loop here
 * is a good idea. The loop should only end when a good year is entered.
 */

int GetYearFromUser(void)
{

Write your function here. 

}

/*
 * Function: PrintCalendar
 * Usage: PrintCalendar(year);
 * ---------------------------
 * This procedure prints a calendar for an entire year.
 */

void PrintCalendar(int year)
{
    int month;

    for (month = 1; month <= 12; month++) {
        PrintCalendarMonth(month, year);
        printf("\n");
    }
}

/*
 * Function: PrintCalendarMonth
 * Usage: PrintCalendarMonth(month, year);
 * ---------------------------------------
 * This procedure prints a calendar for the given month
 * and year.
 */

void PrintCalendarMonth(int month, int year)
{
    int weekday, no_of_days ;

    printf("    %s %d\n", MonthName(month), year);
    printf(" Su Mo Tu We Th Fr Sa\n");
    no_of_days = MonthDays(month, year);
    weekday = FirstDayOfMonth(month, year);
    IndentFirstLine(weekday);
    weekday = PrintDays (no_of_days, weekday);
    if (weekday != SUNDAY) printf("\n");
}


/*
 * Function: IndentFirstLine
 * Usage: IndentFirstLine(weekday);
 * --------------------------------
 * This procedure indents the first line of the calendar
 * by printing enough blank spaces to get to the position
 * on the line corresponding to weekday. It does this simply
 * by spacing over as many spaces are needed so that the numbers
 *  begin printing in the correct columns.
 */

void IndentFirstLine(int weekday)
{
  
Write your function here.

}

/*
 * Function: PrintDays
 * Usage: PrintDays (no_of_days, weekday)
 * --------------------------------
 * This procedure takes the number of days in a month and
 * the first day in that month and prints out the dates in
 * that month in the correct columns. 
 * It returns the value of the day after the last day of
 * the month to the function PrintCalendarMonth.
 * You might use either a switch or if-else statement here.
 */

int PrintDays (int no_of_days, int weekday)
{

  int day;

  for (day = 1; day <= no_of_days; day++) {
    printf(" %2d", day);
    if (weekday == SATURDAY) printf("\n");
    weekday = (weekday + 1) % 7;
  }

  return (weekday);

}



/*
 * Function: MonthDays
 * Usage: ndays = MonthDays(month, year);
 * --------------------------------------
 * MonthDays returns the number of days in the indicated
 * month and year.  The year is required to handle leap years.
 * You may want to use the IsLeapYear function in this function.
 */

int MonthDays(int month, int year)
{

Write your function here. 

}

/*
 * Function: FirstDayOfMonth
 * Usage: weekday = FirstDayOfMonth(month, year);
 * ----------------------------------------------
 * This function returns the day of the week on which the
 * indicated month begins.  This program simply counts
 * forward from January 1, 1900, which was a Monday.
 * It may be useful to use the IsLeapYear function.
 */

int FirstDayOfMonth(int month, int year)
{

Write your function here. 

}


/*
 * Function: MonthName
 * Usage: name = MonthName(month);
 * -------------------------------
 * MonthName converts a numeric month in the range 1-12
 * into the string name for that month.
 */

char * MonthName(int month)
{
    switch (month) {
      case  1: return ("January");
      case  2: return ("February");
      case  3: return ("March");
      case  4: return ("April");
      case  5: return ("May");
      case  6: return ("June");
      case  7: return ("July");
      case  8: return ("August");
      case  9: return ("September");
      case 10: return ("October");
      case 11: return ("November");
      case 12: return ("December");
      default: return ("Illegal month");
    }
}

/*
 * Function: IsLeapYear
 * Usage: if (IsLeapYear(year)) . . .
 * ----------------------------------
 * This function returns 1 if year is a leap year, 0 if not. 
 */

int IsLeapYear(int year)
{

Write your function here. 

}