#include <stdio.h>
#include <stdlib.h>

/*
Write a complete C program that prints a monthly calendar for any month 
in 2012. Your program can assume (and not calculate) that Jan 1, 2012 is 
a Sunday and also that 2012 is a leap year (i.e., February has 29 days).
It is OK to hardcode an integer array in your program that has the number 
of days in each month, e.g., int days[12]={31, 29, 31,....}.

Important: Your program must calculate the calendar for each month. 
You can't simply hardcode a set of printf statements for each month. 
Also, you can't call the calendar utility of the operating system do the job. 
(The 'cal' program that is available in Unix inspired this problem.) 

The month is specified by the user as a number from 1 to 12.
The output must be in the format specified the three sample runs given below.
 
 
> Please enter a month [1-12]: 1

     January 2012
 Su Mo Tu We Th Fr Sa
  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 

 
 
>Please enter a month [1-12]: 3
     March 2012
 Su Mo Tu We Th Fr Sa
              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


 
 >Please enter a month [1-12]: 10
 
     October 2012
 Su Mo Tu We Th Fr Sa
     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
 
*/

void print_month_name(int month)
{
	switch(month)
	{
		case  1: printf("January"); break;
		case  2: printf("February"); break;
		case  3: printf("March"); break;
		case  4: printf("April"); break;
		case  5: printf("May"); break;
		case  6: printf("June"); break;
		case  7: printf("July"); break;
		case  8: printf("August"); break;
		case  9: printf("September"); break;
		case 10: printf("October"); break;
		case 11: printf("November"); break;
		case 12: printf("December"); break;
	}
}

void print_days(int daysInThisMonth, int startDayOfWeek)
{
	int i, day;
	
	for(i=0; i<startDayOfWeek; i++) // print leading spaces
	   printf("   ");
	   
	day=startDayOfWeek;   
	for(i=1; i<=daysInThisMonth; i++)
	{		
		printf("%2d ", i);
		day++;
		if(day%7==0)
		{
			printf("\n");
			day=0;
		}
	}
}

int main()
{
	int i, month;
	int days[12]={31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
	
	// User input and input safety checks
	do
	{
		printf("This program prints a monthly calendar for 2008.\n");
		printf("Please enter a month [1-12]: ");
		scanf(" %d", &month);
	}while((month<1) || (month>12));

	// calucalte the day of the week for the 1st day of the month
	
	int startDayOfWeek=0;// Jan 1, 2012 is a Sunday
	for(i=0; i<month-1; i++)  // don't include the current month
		startDayOfWeek+=days[i];
		
	startDayOfWeek%=7;
	
    // Print the calendar
	printf("\n\n    ");
	print_month_name(month);	
	printf(" 2012\n");
	printf("Su Mo Tu We Th Fr Sa\n");
	print_days(days[month-1], startDayOfWeek);
	printf("\n");
	
	system("pause");
	return 0;
}