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Working out how many hours worked after a certain time

I am working on some custom rules in a time managment system and need to know how many hours in a shift have been before a certain time (19:00pm) and how many hours after. Shifts can start in the evening and finish in the morning so need to take that into account.
So far I have the below (this is just a snippet for one day) however it seems very clumsy and eloborate what I have written, can't help but feel I am missing a simpler solution, anyone have any ideas?
DateTime cutOffTime = new DateTime(DateTime.Now.Year, DateTime.Now.Month, DateTime.Now.Day, 19, 00, 00);
string cutOffTimeOfDay = GetTimeOfDayFromDateTime(cutOffTime);
double baseMondayHours = 10.00;
baseMondayHours = (baseMondayHours - 0.5);
if (GetTimeOfDayOnlyFromDateTime(monday.ShiftStart.Value) == "AM" && GetTimeOfDayOnlyFromDateTime(monday.ShiftEnd.Value) == "PM"
&& monday.ShiftEnd.Value.TimeOfDay < cutOffTime.TimeOfDay)
{
postCutOffMondayHours = 0;
baseMondayHours = monday.HoursWorked.Value;
}
else
{
string endTimeOfDay = GetTimeOfDayFromDateTime(monday.ShiftEnd.Value);
double hoursAfterCutOff = GetDuration(cutOffTimeOfDay, endTimeOfDay);
postCutOffMondayHours = hoursAfterCutOff;
baseMondayHours = (baseMondayHours - hoursAfterCutOff);
}
public static string GetTimeOfDayFromDateTime(DateTime d)
{
return d.ToString("HH:mm") + " " + d.ToString("tt", CultureInfo.InvariantCulture);
}
public static string GetTimeOfDayOnlyFromDateTime(DateTime d)
{
return d.ToString("tt", CultureInfo.InvariantCulture).ToUpper();
}
public static double GetDuration(string startTime, string endTime)
{
DateTime start = DateTime.Parse(startTime);
DateTime end = DateTime.Parse(endTime);
if (start > end)
end = end.AddDays(1);
TimeSpan duration = end.Subtract(start);
return duration.TotalHours;
}

I'm not sure if I'm missing something here, but isn't the built-in operator- of DateTime exactly what you're looking for? It returns the TimeSpan between the 2 DateTime, and if you can guarantee shiftStart < cutoffDateTime < shiftEnd, then you can get the hours worked by just using the TotalHours of TimeSpan (but adding that check is just an additional small if)
var shiftStart = new DateTime(2020, 6, 2, 17, 0, 0);
var shiftEnd = new DateTime(2020, 6, 3, 6, 30, 0);
var cutoffDateTime = new DateTime(2020, 6, 2, 19, 0, 0);
var hoursWorkedBefore = (cutoffDateTime - shiftStart).TotalHours;
var hoursWorkedAfter = (shiftEnd - cutoffDateTime).TotalHours;

DateTime go to first occurrence of hour/minute/second

Given this datetime of January 1 2015 at 23:00 hours:
var someDate = new DateTime(2015, 1, 1, 23, 0, 0);
And given the int 6, which is the desired hour, how do I return the first following datetime where the hour is 6? In this case, someDate and 6 would return a new DateTime of January 2 2015 at 06:00 hours.

I would simply add the hours to the original date and add another day if the result is before the original time:
var someDate = new DateTime(2015, 1, 1, 23, 0, 0);
var result = someDate.Date.AddHours(6); // note the "Date" part
if (result < someDate) result = result.AddDays(1);

You just have to add one day to the date and six hours to the result:
var someDate = new DateTime(2015, 1, 1, 23, 0, 0);
var result = someDate.Date.AddDays(1).AddHours(6);
Note the use of Date property - it will give you the start od the day and from there it's easy to navigate forward.

Try this:
while(someDate.Hour != 6){
someDate = someDate.AddHours(1);
}

Assuming you meant 24h clock, you can try this:
public DateTime GetDate(DateTime someDate,int hour)
{
return someDate.Hour>=hour? someDate.Date.AddDays(1).AddHours(6):someDate.Date.AddHours(6);
}

Something like this should do it:
public DateTime FollowingHour(DateTime start, int hour)
{
DateTime atHour = start.Date.AddHours(6);
if(atHour < start)
{
atHour += TimeSpan.FromDays(1);
}
return atHour;
}

How to find all certain days of week in the given year?

My task is to find all Friday, 13 in a year that user inputs.
Can somebody explain how to do it? (I'm a beginner in c#)

int year = 2015;
for(int m=1; m<=12; m++)
{
var dt = new DateTime(year, m, 13);
if (dt.DayOfWeek == DayOfWeek.Friday)
Console.WriteLine(dt.ToShortDateString());
}

To obtain the dates you may use Linq:
var dates = Enumerable
.Range(1, 12) // All months
.Select(month => new DateTime(2015, month, 13))
.Where(date => date.DayOfWeek == DayOfWeek.Friday);
To print out them
Console.WriteLine(String.Join(Environment.NewLine, dates));

If you want to get these dates in Gregorian Calender, you can use a combination of a loop, DateTime constructor and DayOfWeek enumeration like;
int year = 2015;
for (int i = 1; i < 13; i++)
{
if(new DateTime(year, i, 13).DayOfWeek == DayOfWeek.Friday)
Console.WriteLine(new DateTime(year, i, 13));
}
For 2015, result will be;
13.02.2015 00:00:00
13.03.2015 00:00:00
13.11.2015 00:00:00
If you want to number of months, you can use .Month property of the result like;
Console.WriteLine((new DateTime(year, i, 13)).Month);
If you want to get your month names based on your CurrentCulture, you can use custom MMMM specifier like;
Console.WriteLine((new DateTime(year, i, 13)).ToString("MMMM"));
Also you can use Enumerable.Range like;
List<int> monthList = Enumerable.Range(1, 12).
Where(d => new DateTime(2015, d, 13).DayOfWeek == DayOfWeek.Friday).
ToList(); // {2, 3, 11}
or
List<string> monthList = Enumerable.Range(1, 12).
Where(d => new DateTime(2015, d, 13).DayOfWeek == DayOfWeek.Friday).
Select(m => new DateTime(2015, m, 13).ToString("MMMM", CultureInfo.InvariantCulture)).
ToList(); // {February, March, November}

Try to inspire by the code showed in that thread:
Finding every friday from start date till the end of the year
(of course you will have to check if selected Friday is 13th)

It can be done like this using linq.
var year = 2015;
var months = new[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 };
var unluckyDays = months.Select(m => new DateTime(year, m, 13)).Where(dt => dt.DayOfWeek == DayOfWeek.Friday);
The first Select statement projects the list of integers into a list of datetimes representing the 13th of each month in the year specified.
Then simply filter this list to those where the day of the week is Friday.

DateTime objects have a property on them called DayOfWeek. You can utilize this to help you figure out if a date supplied returns a DayOfWeek Value of Friday: see below:
static void Main(string[] args)
{
for (var i = 1; i < 12; i++)
{
DateTime date = new DateTime(2015, i, 13);
if (date.DayOfWeek == DayOfWeek.Friday)
Console.WriteLine(date.ToShortDateString());
}
Console.ReadLine();
}

Yes, it is quite simple
int year = 2014;
DateTime day = new DateTime(2014,1,1);
while (day.Year == year)
{
if (day.DayOfWeek == DayOfWeek.Friday && day.Day == 13)
{
Console.WriteLine(day);
}
day = day.AddDays(1);
}
You init a DateTime variable in the start of the year
Then you loop over each day of the year in this code I printed it
You can find more info of the DateTime class here
DateTime Day of the week
DateTime referenc in MSDN

C# get whole hour values between 2 datetime objects

I am trying to get the affected hours between 2 datetime and all i found was a python solution.
For example 'start' is 09:30 and 'end' is 14:00 (same day). The values I'd like returned are
[9:00, 10:00, 11:00, 12:00, 13:00, 14:00]
Python get whole hour values between 2 datetime objects
I can't seem to find any equivalent to C#.

So you want a list of all hours between both dates? You can use this query:
TimeSpan ts = dt2 - dt1;
IEnumerable<int> hoursBetween = Enumerable.Range(0, (int)ts.TotalHours)
.Select(i => dt1.AddHours(i).Hour);
Sample dates:
DateTime dt1 = new DateTime(2013, 07, 08, 15, 50, 00);
DateTime dt2 = new DateTime(2013, 07, 10, 19, 30, 00);
TimeSpan ts = dt2 - dt1;
IEnumerable<int> hoursBetween = Enumerable.Range(0, (int)ts.TotalHours)
.Select(i => dt1.AddHours(i).Hour);
foreach (int hour in hoursBetween)
Console.WriteLine(hour);
Output:
15
16
17
18
19
20
21
22
23
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17

The following will return the total hours between the 2 DateTime objects:
(datevalue1 - datevalue2).TotalHours
And for a custom behavior,such as displaying a list of hours, use a simple custom method on that Timespan created to get a list of hours in your desired format.
Code suggestion of the top of my head:
public List<String> GenerateHours(DateTime t1,DateTime t2){
if ((t2-t1).TotalHours >24)){
//decide what to do.
return null;
}else{
var currentHour = t2.Hour;
var list = new List<String>();
for (int i=0;i<(t2-t1).TotalHours;i++){
if (currentHour<10){
list.Add("0"+currentHour+":00");
}else if (currentHour>=10){
list.Add(currentHour+":00");
}
currentHour= (currentHour+1)%24;
}
return list;
}
}

public IEnumerable<DateTime> GetHoursBetween(DateTime start, DateTime end)
{
DateTime first = start.Date.AddHours(start.Hour);
for (DateTime dateTime = first; dateTime <= end; dateTime = dateTime.AddHours(1))
{
yield return dateTime;
}
}

TimeSpan ts = DateTime1 - DateTime2;
double totalHours = ts.TotalHours;
From MSDN: "Gets the value of the current TimeSpan structure expressed in whole and fractional hours."
EDIT: ok, now I see what you're asking for. How about this:
var d1 = DateTime.Today.AddHours(9.5);
var d2 = DateTime.Today.AddHours(14);
var first = new DateTime(d1.Year, d1.Month, d1.Day, d1.Minute == 0 ? d1.Hour : d1.Hour + 1, 0, 0);
var second = new DateTime(d2.Year, d2.Month, d2.Day, d2.Minute == 0 ? d2.Hour : d2.Hour + 1, 0, 0);
TimeSpan ts = second - first;
//returns DateTimes affected. I.e., Today at, [10:00, 11:00, 12:00, 13:00, 14:00]
IEnumerable<DateTime> dates = Enumerable.Range(0, (int)ts.TotalHours + 1).Select(hour => first.AddHours(hour));
//Or, if you just want the HOURs
//returns just ints: i.e., DateTimes 10,11,12,13,14
IEnumerable<int> hours = Enumerable.Range(0, (int)ts.TotalHours + 1).Select(hour => first.AddHours(hour).Hour);
The first method is needed if you actually have dates that span days. If you DON'T, then the second method that just returns the hours would work fine.

This should do the trick. Tested in LinqPad.
var startDate = new DateTime(2013, 8, 7, 9, 30, 0);
var endDate = new DateTime(2013, 8, 7, 14, 0, 0);
List<string> times = new List<string>();
var currentTime = startDate;
if (currentTime.Minute != 0 || currentTime.Second != 0) {
// Get next hour
currentTime = currentTime.AddHours(1).AddMinutes(currentTime.Minute * -1);
}
while (currentTime <= endDate) {
times.Add(string.Format("{0:00}:00", currentTime.Hour));
currentTime = currentTime.AddHours(1);
}

(int)Math.Abs((date1 - date2).TotalHours)

Simply subtract them and get the total of hours from the result. Something like this:
var totalHours = (dateTime1 - dateTime2).TotalHours;

Maybe something like this would work?
public static List<DateTime> GetAffectedHours(DateTime start, DateTime end)
{
List<DateTime> result = new List<DateTime>();
// Strip start of its minutes/seconds/etc
DateTime initial = new DateTime(start.Year, start.Month, start.Day, start.Hour, 0, 0);
// Go ahead and get the next hour
DateTime iterator = initial.AddHours(1.0);
// if it is still before the end
while (iterator < end)
{
// add it to the results list
result.Add(iterator);
// and get the next hour
iterator = iterator.AddHours(1.0);
}
return result;
}

You can use a For loop
List<int> allHoursBetween = new List<int>();
for (DateTime d = myStartDate; d <= myEndDate; d = d.AddHours(1))
allHoursBetween.Add(d.Hour);

Select Only Fourth Sunday of each month

I am stuck for sometime now, now need your help.
I want to display in a dropdown only fourth Sunday of each month, say from 1-Sep-2010 to 31-Aug-2011
I only want fourth Sunday in dropdown list, how to do it using asp.net C#
Regards

Here is an approach that uses a little LINQ and the knowledge that the fourth Sunday will occur between the 22nd and 28th of a month, inclusive.
DateTime startDate = new DateTime(2010, 9, 1);
DateTime endDate = startDate.AddYears(1).AddDays(-1);
List<DateTime> fourthSundays = new List<DateTime>();
DateTime currentDate = startDate;
while (currentDate < endDate)
{
// we know the fourth sunday will be the 22-28
DateTime fourthSunday = Enumerable.Range(22, 7).Select(day => new DateTime(currentDate.Year, currentDate.Month, day)).Single(date => date.DayOfWeek == DayOfWeek.Sunday);
fourthSundays.Add(fourthSunday);
currentDate = currentDate.AddMonths(1);
}
You can then bind that List<DateTime> to the dropdown or skip the list itself in favor of adding the items as you generate them to the dropdown, like below.
yourDropdown.Items.Add(new ListItem(fourthSunday.ToString()));
For giggles, you can do the whole thing in a LINQ statement and skip (most of) the variables.
DateTime startDate = new DateTime(2010, 9, 1);
IEnumerable<DateTime> fourthSundays =
Enumerable.Range(0, 12)
.Select(item => startDate.AddMonths(item))
.Select(currentMonth =>
Enumerable.Range(22, 7)
.Select(day => new DateTime(currentMonth.Year, currentMonth.Month, day))
.Single(date => date.DayOfWeek == DayOfWeek.Sunday)
);

Got bored so here you go. Two helper methods one retrieves the Week if it exist, and the other iterates through the months
class Program
{
static void Main(string[] args)
{
DateTime startDate = new DateTime(2010, 09, 1);
foreach(DateTime dt in EachMonth( new DateTime(2010, 09, 1), new DateTime(2011, 09, 1))){
DateTime? result = GetDayByWeekOffset(DayOfWeek.Sunday, dt, 4);
Console.WriteLine("Sunday:" + (result.HasValue?result.Value.ToString("MM-dd-yyyy"):"null"));
}
Console.ReadKey();
}
public static DateTime? GetDayByWeekOffset(DayOfWeek day, DateTime month, int weekOffSet)
{
//First day of month
DateTime firstDayOfMonth = month.AddDays((-1 * month.Day) + 1);
//
int daysOffSet;
daysOffSet= ((int)day + 7 - (int)firstDayOfMonth.DayOfWeek) % 7;
DateTime firstDay = month.AddDays(daysOffSet);
// Add the number of weeks specified
DateTime resultDate = firstDay.AddDays((weekOffSet - 1) * 7);
if (resultDate.Month != firstDayOfMonth.Month){
return null;
}else{
return resultDate;
}
}
public static IEnumerable<DateTime> EachMonth(DateTime from, DateTime thru)
{
for (var month = from.Date; month.Date <= thru.Date; month = month.AddMonths(1))
yield return month;
}
}

Anthony's answer above is nice, I like it a lot. As an alternate, here is a method which is parameterized for the day of the week and the week number (i.e. if you need other combinations, like 4th Sunday, 3rd Friday, etc.) with some comments.
Call it like this for your case:
List<DateTime> sundays = DateInstances(new DateTime(2010, 9, 1), new DateTime(2011, 8, 31), DayOfWeek.Sunday, 4);
And the method itself:
public List<DateTime> DateInstances(DateTime start, DateTime end, DayOfWeek day, int weeks)
{
if (start > end)
throw new ArgumentOutOfRangeException("end", "The start date must occur before the end date");
List<DateTime> results = new List<DateTime>();
DateTime temp = start;
while (temp < end)
{
DateTime firstWeekday = new DateTime(temp.Year, temp.Month, 1);
//increment to the given day (i.e. if we want the 4th sunday, we must find the first sunday of the month)
while (firstWeekday.DayOfWeek != day)
firstWeekday = firstWeekday.AddDays(1);
//add the number of weeks (note: we already have the first instance, so subtract 1)
firstWeekday = firstWeekday.AddDays(7 * (weeks - 1));
//make sure we haven't gone over to the next month
if (firstWeekday.Month == temp.Month)
results.Add(firstWeekday);
//let's not loop forever ;)
temp = temp.AddMonths(1);
}
return results;
}