Get the first day of every month.

[sita kalidindi]

Hi All,
I need to write a code where i get the first date of every month and display those values.I would like to know how to proceed in order to achieve that?

[hamsterman]

You mean you want to know if it's Monday or etc? Then, assuming that Monday is 0, Tuesday is 1, ..., the first day of a month is the first day of the previous month, and the number of days in that month and do modulo (%) 7.

[sita kalidindi]

Hello Hamsterman,
Thanks for your response.If i enter month 2/1/2012 then i need to get 3/1/2012 .....12/1/2012,1/1/2013.As u mentioned that i should write number of days in a month is it the right way to write ((firstday+ 30)%7).Do i need to write it for all the months?

[hamsterman]

You don't need to repeat the same code 12 times. Loops are for that. You'll need a method to get the number of says in nth month though. This could be

int days_in_month(int m /*0-11*/,bool leap) {
   int days[] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
   if(leap && m==1) return 29;
   else return days[m];
} 

Figure out how to tell if it's a leap year. I think there are code snippets in wikipedia..

[sita kalidindi]

void E::dates()
{
int month;
int year;
int day;
E et;
Date* dt;
d=new Date;

month=dt->getMonth(); //Get the month which is set(ex:1)
year=dt->getYear(); //Get the year which is set(ex:2010)
day=dt->getDay(); //Get the year which is set(ex:1)

bool leapyear = false; //Check whether the year is a leap year

if(year % 4 == 0)
{
if(year % 100 !=0)
leapyear = true;
}

for(month;month<=6;month++) //Need to push the elements of first 6 months.
{
dt->setDate(day, month,year);
dts.push_back(dt); //dts is the vector of Date pointers.
}


}

Problem with this code:After the first element is inserted with value 1/1/2011 then when i try to insert the second element during debugging i am able to see the value of month as 2 but in the result even the first value in the vector also set to 1/2/2011.So i am getting the below output for 6 months:
1/6/2011
1/6/2011
Why those values are being reset?Do guide me.

[Duthomhas]

Where to go for stuff about dates:
http://www.faqs.org/faqs/calendars/faq/part1/index.html

There is in there also a simple method to determine the day of week for a specific date, as well as methods for determining whether it is a leap year.

Hope this helps.

[sita kalidindi]

Hi,
I would like to know why the values are being overwritten with latest value when trying to insert the values in to a vector?

[hamsterman]

You have a vector of pointers. You change the object dt points to and push dt. Thus all pointers point to the same location as dt. The quickest way to solve this is to remove the * from declaration of dts (making it an vector of Date objects rather than pointers) and add it to line dts.push_back(*dt);. There is no need to use pointers anywhere here though at all.

[sita kalidindi]

Hello Hamsterman,
Thanks for your help.It worked.I have one more thing to get clarified.While displaying i would like to have this format Jan 1 Wed 2011 etc.Basically i wanted to display along with the day of week.This is the below code but it is not working.By default it is same for all the values Jan 1 Wed 2011,Jan 1 Wed 2011 etc.

vector <Date>::const_iterator iter; //vector of date objects

for(iter=dts.begin();iter!=dts.end();++iter) //Traversing through the vector
{
Date dat;
printMonth(dat.getMonth(),dayofweek(1,dat.getMonth(),dat.getYear()),dat.getYear());
}

//Finds what day of the week the year starts on
int E::dayofweek(const int day, const int month, const int year) const
{
int a,y,m;
a=(14-month)/12;
y=year-a;
m= month+12*a-2;
return (day+y+y/4-y/100 + y/400 + (31*m/12))%7;
}


void E::printMonth(const int month, const int startday, const bool leap) const
{

string Days[7] = {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"};

string Months[13] = {" ", "January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"};
int DaysinMonth[13] = {0,31,28,31,30,31,30,31,31,30,31,30,31};
//Checks to see if it is a leap year and changes the days in February accordingly.
if(leap)
DaysinMonth[2] = 29;

cout<<setw(10)<<Months[month]<<setw(15)<<Days[startday]<<setw(15)<<dt->getDay()<<setw(15)<<dt->getYear();
cout << endl;
}
Thanks in advance.

[hamsterman]

You forgot dat = *iter; ? Now dat has no relation to the contents of dts.

[sita kalidindi]

Hello Hamsterman,
Thanks a lot.It helped me a lot.One more thing i wanted to try for any given date it should display 6 months from that date.Ex:1/2/2011 then it should display till July 1/7/2011.
I tried with both for loops:
for(month;month<=6;month++) //Need to push the elements of first 6 months.
{
dt->setDate(day, month,year);
dts.push_back(dt); //dts is the vector of Date pointers.
}

Output will be from Feb to June since i wrote the condition as month<=6.

for(month=month+6;month<=12;month++) //Need to push the elements of first 6 months.
{
dt->setDate(day, month,year);
dts.push_back(dt); //dts is the vector of Date pointers.
}
Output is starting from August since i wrote the start condition as month+6.

What can be the exact condition?

Thanks in advance.