horizontalcalendar.cpp

/* The following code prints the calendar of the year input by the user */

#include<bits/stdc++.h>
#define f(i,a,n) for(int i=a ;i<n ;i++)
using namespace std;

/* The integer function dayofweek returns a number corresponding to the day at which 1st January of input year falls i.e. day at which 01/01/.... occurs
Day		Value of n
Monday 		1
Tuesday		2
Wednesday	3
Thursday	4
Friday		5
Saturday	6
Sunday		0 */

int dayofweek(int y)  
{  
	int d=1,m=1;
    static int t[] = { 0, 3, 2, 5, 0, 3, 
                       5, 1, 4, 6, 2, 4 };  
    y -= m < 3;  //If m<3, return y-1, else return y
	
    //Using Tomohiko Sakamoto’s Algorithm
    return ( y + y / 4 - y / 100 +  y / 400 + t[m - 1] + d) % 7;  
}

//The boolean function checkYear is used to check is the input year is leap year or not. If it is a leap year, true is returned, else false is returned.
bool checkYear(int year)  
{  

    if (year % 400 == 0)  
        return true;  
  
    if (year % 100 == 0)  
        return false;  
  
    if (year % 4 == 0)
        return true;  
        
    return false;  
}  

int main()
{
	int y;
	cout<<"Enter year : ";
	cin>>y;
	
	int n = dayofweek(y);
//	cout<<n<<endl<<endl;
	/* The following lines modify the value of n to give the following result
	Day		Value of n
	Monday 		1
	Tuesday		2
	Wednesday	3
	Thursday	4
	Friday		5
	Saturday	6
	Sunday		7 */
	
	n%=7;
	if(!n)
	n=7;
	int m=1,d=31,febday;
	
	//Set containing all months of the year
	string month[12]={"January", "February" ,"March" , "April" , "May" ,"June" ,"July" , "August" ,"September" ,"October" ,"November" ,"December"};
	int i=1;
	
//	If input year is leap year, number of days in Februrary are 29, else 28.
	if(checkYear(y))
	febday=29;
	else
	febday=28;
	
	while(i<=12)
	{
		//Print Current Month of the year
		cout<<month[i-1]<<" "<<y<<endl;
		
		//Print all days of the week
		int j=1;
		cout<<"Mon \t"<<"Tue \t"<<"Wed \t"<<"Thu \t"<<"Fri \t"<<"Sat \t"<<"Sun \t"<<endl;
		
		//Print tab until the day corresponding to 01/../.... is reached
		f(k,1,n)
		cout<<"\t";
		
		//If Current month is February, set number of days as determined in line 72:75
		if(i==2)
		d=febday;
		
		//Run 'for loop' from 1 to d+1 where d is the number of days in that month
		f(k,1,d+1)
		{
			//Print dates while adjusting space for two digit numbers
			if(k<10)
			cout<<k<<"   \t";
			
			else
			cout<<k<<"  \t";
			
			n++;
			//Reset day of the week to Monday (i.e. 1) if it becomes greater than Sunday (i.e. 7)
			if(n>7)
			{
				n=1;
				cout<<"\n";
			}			
		}
		
		//If Current month is July, set number of days for next iteration as 31 (August), else set to 30
		if(d==31 && i!=7)
		d=30;
		else
		d=31;
		
		cout<<endl<<endl;
		i++;
		
	}
	
}