Check if less than 7 days before ending [duplicate] - c#

I see that this question has been answered for Java, JavaScript, and PHP, but not C#. So, how might one calculate the number of days between two dates in C#?


Assuming StartDate and EndDate are of type DateTime:
(EndDate - StartDate).TotalDays


The top answer is correct, however if you would like only WHOLE days as an int and are happy to forgo the time component of the date then consider:
(EndDate.Date - StartDate.Date).Days
Again assuming StartDate and EndDate are of type DateTime.


Use TimeSpan object which is the result of date substraction:
DateTime d1;
DateTime d2;
return (d1 - d2).TotalDays;


I think this will do what you want:
DateTime d1 = DateTime.Now;
DateTime d2 = DateTime.Now.AddDays(-1);
TimeSpan t = d1 - d2;
double NrOfDays = t.TotalDays;


DateTime xmas = new DateTime(2009, 12, 25);
double daysUntilChristmas = xmas.Subtract(DateTime.Today).TotalDays;


// Difference in days, hours, and minutes.
TimeSpan ts = EndDate - StartDate;
// Difference in days.
int differenceInDays = ts.Days; // This is in int
double differenceInDays= ts.TotalDays; // This is in double
// Difference in Hours.
int differenceInHours = ts.Hours; // This is in int
double differenceInHours= ts.TotalHours; // This is in double
// Difference in Minutes.
int differenceInMinutes = ts.Minutes; // This is in int
double differenceInMinutes= ts.TotalMinutes; // This is in double
You can also get the difference in seconds, milliseconds and ticks.


In case someone wants numer of whole days as a double (a, b of type DateTime):
(a.Date - b.Date).TotalDays


There often is a debate on time (hours) when it comes to counting days between two dates. The responses to the question and their comments show no exception.
Considering StartDate and EndDate are of type DateTime: if performance is not a concern, I would strongly recommend documenting your calculation through intermediate conversions. For example, (EndDate - StartDate).Days is unintuitive because rounding will depend on the hour component of StartDate and EndDate.
If you want the duration in days to include fractions of days, then as already suggested
use (EndDate - StartDate).TotalDays.
If you want the duration to reflect
the distance between two days, then use (EndDate.Date - StartDate.Date).Days
If you want the duration to reflect the
duration between the morning of the start date, and the evening of
the end date (what you typically see in project management software), then use
(EndDate.Date - StartDate.Date).Days + 1


You can try this
EndDate.Date.Subtract(DateTime.Now.Date).Days


Using a timespan would solve the problems as it has many attributes:
DateTime strt_date = DateTime.Now;
DateTime end_date = Convert.ToDateTime("10/1/2017 23:59:59");
//DateTime add_days = end_date.AddDays(1);
TimeSpan nod = (end_date - strt_date);
Console.WriteLine(strt_date + "" + end_date + "" + "" + nod.TotalHours + "");
Console.ReadKey();


For a and b as two DateTime types:
DateTime d = DateTime.Now;
DateTime c = DateTime.Now;
c = d.AddDays(145);
string cc;
Console.WriteLine(d);
Console.WriteLine(c);
var t = (c - d).Days;
Console.WriteLine(t);
cc = Console.ReadLine();


For beginners like me that will stumble upon this tiny problem, in a simple line, with sample conversion to int:
int totalDays = Convert.ToInt32((DateTime.UtcNow.Date - myDateTime.Date).TotalDays);
This calculates the total days from today (DateTime.UtcNow.Date) to a desired date (myDateTime.Date).
If myDateTime is yesterday, or older date than today, this will give a positive (+) integer result.
On the other side, if the myDateTime is tomorrow or on the future date, this will give a negative (-) integer result due to rules of addition.
Happy coding! ^_^


First declare a class that will return later:
public void date()
{
Datetime startdate;
Datetime enddate;
Timespan remaindate;
startdate = DateTime.Parse(txtstartdate.Text).Date;
enddate = DateTime.Parse(txtenddate.Text).Date;
remaindate = enddate - startdate;
if (remaindate != null)
{
lblmsg.Text = "you have left with " + remaindate.TotalDays + "days.";
}
else
{
lblmsg.Text = "correct your code again.";
}
}
protected void btncal_Click(object sender, EventArgs e)
{
date();
}
Use a button control to call the above class. Here is an example:


You can use the code below:
int DateDifInSecond = EndDate.Subtract(StartDate).TotalSeconds


Get the difference between the two dates and then get the days from:
int total_days = (EndDate - StartDate).TotalDays


try this truly worked Get actual days diff. date format is "dd/MM/yyyy"
string[] d1 = txtFromDate.Values.Split('/');
string[] d2 = txtToDate.Values.Split('/');
DateTime FrmDt = new DateTime(Convert.ToInt32(d1[2]), Convert.ToInt32(d1[1]), Convert.ToInt32(d1[0]));
DateTime ToDt = new DateTime(Convert.ToInt32(d2[2]), Convert.ToInt32(d2[1]), Convert.ToInt32(d2[0]));
TimeSpan TDiff = ToDt.Subtract(FrmDt);
String DaysDiff = TDiff.TotalDays.ToString();


protected void Calendar1_SelectionChanged(object sender, EventArgs e)
{
DateTime d = Calendar1.SelectedDate;
// int a;
TextBox2.Text = d.ToShortDateString();
string s = Convert.ToDateTime(TextBox2.Text).ToShortDateString();
string s1 = Convert.ToDateTime(Label7.Text).ToShortDateString();
DateTime dt = Convert.ToDateTime(s).Date;
DateTime dt1 = Convert.ToDateTime(s1).Date;
if (dt <= dt1)
{
Response.Write("<script>alert(' Not a valid Date to extend warranty')</script>");
}
else
{
string diff = dt.Subtract(dt1).ToString();
Response.Write(diff);
Label18.Text = diff;
Session["diff"] = Label18.Text;
}
}

Related

Net Core 2 StartOfWeek [duplicate]

How do I find the start of the week (both Sunday and Monday) knowing just the current time in C#?
Something like:
DateTime.Now.StartWeek(Monday);

Use an extension method:
public static class DateTimeExtensions
{
public static DateTime StartOfWeek(this DateTime dt, DayOfWeek startOfWeek)
{
int diff = (7 + (dt.DayOfWeek - startOfWeek)) % 7;
return dt.AddDays(-1 * diff).Date;
}
}
Which can be used as follows:
DateTime dt = DateTime.Now.StartOfWeek(DayOfWeek.Monday);
DateTime dt = DateTime.Now.StartOfWeek(DayOfWeek.Sunday);

The quickest way I can come up with is:
var sunday = DateTime.Today.AddDays(-(int)DateTime.Today.DayOfWeek);
If you would like any other day of the week to be your start date, all you need to do is add the DayOfWeek value to the end
var monday = DateTime.Today.AddDays(-(int)DateTime.Today.DayOfWeek + (int)DayOfWeek.Monday);
var tuesday = DateTime.Today.AddDays(-(int)DateTime.Today.DayOfWeek + (int)DayOfWeek.Tuesday);

A little more verbose and culture-aware:
System.Globalization.CultureInfo ci =
System.Threading.Thread.CurrentThread.CurrentCulture;
DayOfWeek fdow = ci.DateTimeFormat.FirstDayOfWeek;
DayOfWeek today = DateTime.Now.DayOfWeek;
DateTime sow = DateTime.Now.AddDays(-(today - fdow)).Date;

Using Fluent DateTime:
var monday = DateTime.Now.Previous(DayOfWeek.Monday);
var sunday = DateTime.Now.Previous(DayOfWeek.Sunday);

Ugly but it at least gives the right dates back
With start of week set by system:
public static DateTime FirstDateInWeek(this DateTime dt)
{
while (dt.DayOfWeek != System.Threading.Thread.CurrentThread.CurrentCulture.DateTimeFormat.FirstDayOfWeek)
dt = dt.AddDays(-1);
return dt;
}
Without:
public static DateTime FirstDateInWeek(this DateTime dt, DayOfWeek weekStartDay)
{
while (dt.DayOfWeek != weekStartDay)
dt = dt.AddDays(-1);
return dt;
}

Let's combine the culture-safe answer and the extension method answer:
public static class DateTimeExtensions
{
public static DateTime StartOfWeek(this DateTime dt, DayOfWeek startOfWeek)
{
System.Globalization.CultureInfo ci = System.Threading.Thread.CurrentThread.CurrentCulture;
DayOfWeek fdow = ci.DateTimeFormat.FirstDayOfWeek;
return DateTime.Today.AddDays(-(DateTime.Today.DayOfWeek- fdow));
}
}

This would give you the preceding Sunday (I think):
DateTime t = DateTime.Now;
t -= new TimeSpan ((int) t.DayOfWeek, 0, 0, 0);

For Monday
DateTime startAtMonday = DateTime.Now.AddDays(DayOfWeek.Monday - DateTime.Now.DayOfWeek);
For Sunday
DateTime startAtSunday = DateTime.Now.AddDays(DayOfWeek.Sunday- DateTime.Now.DayOfWeek);

This may be a bit of a hack, but you can cast the .DayOfWeek property to an int (it's an enum and since its not had its underlying data type changed it defaults to int) and use that to determine the previous start of the week.
It appears the week specified in the DayOfWeek enum starts on Sunday, so if we subtract 1 from this value that'll be equal to how many days the Monday is before the current date. We also need to map the Sunday (0) to equal 7 so given 1 - 7 = -6 the Sunday will map to the previous Monday:-
DateTime now = DateTime.Now;
int dayOfWeek = (int)now.DayOfWeek;
dayOfWeek = dayOfWeek == 0 ? 7 : dayOfWeek;
DateTime startOfWeek = now.AddDays(1 - (int)now.DayOfWeek);
The code for the previous Sunday is simpler as we don't have to make this adjustment:-
DateTime now = DateTime.Now;
int dayOfWeek = (int)now.DayOfWeek;
DateTime startOfWeek = now.AddDays(-(int)now.DayOfWeek);

using System;
using System.Globalization;
namespace MySpace
{
public static class DateTimeExtention
{
// ToDo: Need to provide culturaly neutral versions.
public static DateTime GetStartOfWeek(this DateTime dt)
{
DateTime ndt = dt.Subtract(TimeSpan.FromDays((int)dt.DayOfWeek));
return new DateTime(ndt.Year, ndt.Month, ndt.Day, 0, 0, 0, 0);
}
public static DateTime GetEndOfWeek(this DateTime dt)
{
DateTime ndt = dt.GetStartOfWeek().AddDays(6);
return new DateTime(ndt.Year, ndt.Month, ndt.Day, 23, 59, 59, 999);
}
public static DateTime GetStartOfWeek(this DateTime dt, int year, int week)
{
DateTime dayInWeek = new DateTime(year, 1, 1).AddDays((week - 1) * 7);
return dayInWeek.GetStartOfWeek();
}
public static DateTime GetEndOfWeek(this DateTime dt, int year, int week)
{
DateTime dayInWeek = new DateTime(year, 1, 1).AddDays((week - 1) * 7);
return dayInWeek.GetEndOfWeek();
}
}
}

Putting it all together, with Globalization and allowing for specifying the first day of the week as part of the call we have
public static DateTime StartOfWeek ( this DateTime dt, DayOfWeek? firstDayOfWeek )
{
DayOfWeek fdow;
if ( firstDayOfWeek.HasValue )
{
fdow = firstDayOfWeek.Value;
}
else
{
System.Globalization.CultureInfo ci = System.Threading.Thread.CurrentThread.CurrentCulture;
fdow = ci.DateTimeFormat.FirstDayOfWeek;
}
int diff = dt.DayOfWeek - fdow;
if ( diff < 0 )
{
diff += 7;
}
return dt.AddDays( -1 * diff ).Date;
}

Step 1:
Create a static class
public static class TIMEE
{
public static DateTime StartOfWeek(this DateTime dt, DayOfWeek startOfWeek)
{
int diff = (7 + (dt.DayOfWeek - startOfWeek)) % 7;
return dt.AddDays(-1 * diff).Date;
}
public static DateTime EndOfWeek(this DateTime dt, DayOfWeek startOfWeek)
{
int diff = (7 - (dt.DayOfWeek - startOfWeek)) % 7;
return dt.AddDays(1 * diff).Date;
}
}
Step 2: Use this class to get both start and end day of the week
DateTime dt = TIMEE.StartOfWeek(DateTime.Now ,DayOfWeek.Monday);
DateTime dt1 = TIMEE.EndOfWeek(DateTime.Now, DayOfWeek.Sunday);

var now = System.DateTime.Now;
var result = now.AddDays(-((now.DayOfWeek - System.Threading.Thread.CurrentThread.CurrentCulture.DateTimeFormat.FirstDayOfWeek + 7) % 7)).Date;

This would give you midnight on the first Sunday of the week:
DateTime t = DateTime.Now;
t -= new TimeSpan ((int) t.DayOfWeek, t.Hour, t.Minute, t.Second);
This gives you the first Monday at midnight:
DateTime t = DateTime.Now;
t -= new TimeSpan ((int) t.DayOfWeek - 1, t.Hour, t.Minute, t.Second);

Try with this in C#. With this code you can get both the first date and last date of a given week. Here Sunday is the first day and Saturday is the last day, but you can set both days according to your culture.
DateTime firstDate = GetFirstDateOfWeek(DateTime.Parse("05/09/2012").Date, DayOfWeek.Sunday);
DateTime lastDate = GetLastDateOfWeek(DateTime.Parse("05/09/2012").Date, DayOfWeek.Saturday);
public static DateTime GetFirstDateOfWeek(DateTime dayInWeek, DayOfWeek firstDay)
{
DateTime firstDayInWeek = dayInWeek.Date;
while (firstDayInWeek.DayOfWeek != firstDay)
firstDayInWeek = firstDayInWeek.AddDays(-1);
return firstDayInWeek;
}
public static DateTime GetLastDateOfWeek(DateTime dayInWeek, DayOfWeek firstDay)
{
DateTime lastDayInWeek = dayInWeek.Date;
while (lastDayInWeek.DayOfWeek != firstDay)
lastDayInWeek = lastDayInWeek.AddDays(1);
return lastDayInWeek;
}

I tried several, but I did not solve the issue with a week starting on a Monday, resulting in giving me the coming Monday on a Sunday. So I modified it a bit and got it working with this code:
int delta = DayOfWeek.Monday - DateTime.Now.DayOfWeek;
DateTime monday = DateTime.Now.AddDays(delta == 1 ? -6 : delta);
return monday;

The same for end of the week (in style of Compile This's answer):
public static DateTime EndOfWeek(this DateTime dt)
{
int diff = 7 - (int)dt.DayOfWeek;
diff = diff == 7 ? 0 : diff;
DateTime eow = dt.AddDays(diff).Date;
return new DateTime(eow.Year, eow.Month, eow.Day, 23, 59, 59, 999) { };
}

Thanks for the examples. I needed to always use the "CurrentCulture" first day of the week and for an array I needed to know the exact Daynumber.. so here are my first extensions:
public static class DateTimeExtensions
{
//http://stackoverflow.com/questions/38039/how-can-i-get-the-datetime-for-the-start-of-the-week
//http://stackoverflow.com/questions/1788508/calculate-date-with-monday-as-dayofweek1
public static DateTime StartOfWeek(this DateTime dt)
{
//difference in days
int diff = (int)dt.DayOfWeek - (int)CultureInfo.CurrentCulture.DateTimeFormat.FirstDayOfWeek; //sunday=always0, monday=always1, etc.
//As a result we need to have day 0,1,2,3,4,5,6
if (diff < 0)
{
diff += 7;
}
return dt.AddDays(-1 * diff).Date;
}
public static int DayNoOfWeek(this DateTime dt)
{
//difference in days
int diff = (int)dt.DayOfWeek - (int)CultureInfo.CurrentCulture.DateTimeFormat.FirstDayOfWeek; //sunday=always0, monday=always1, etc.
//As a result we need to have day 0,1,2,3,4,5,6
if (diff < 0)
{
diff += 7;
}
return diff + 1; //Make it 1..7
}
}

Here is a correct solution. The following code works regardless if the first day of the week is a Monday or a Sunday or something else.
public static class DateTimeExtension
{
public static DateTime GetFirstDayOfThisWeek(this DateTime d)
{
CultureInfo ci = System.Threading.Thread.CurrentThread.CurrentCulture;
var first = (int)ci.DateTimeFormat.FirstDayOfWeek;
var current = (int)d.DayOfWeek;
var result = first <= current ?
d.AddDays(-1 * (current - first)) :
d.AddDays(first - current - 7);
return result;
}
}
class Program
{
static void Main()
{
System.Threading.Thread.CurrentThread.CurrentCulture = CultureInfo.GetCultureInfo("en-US");
Console.WriteLine("Current culture set to en-US");
RunTests();
Console.WriteLine();
System.Threading.Thread.CurrentThread.CurrentCulture = CultureInfo.GetCultureInfo("da-DK");
Console.WriteLine("Current culture set to da-DK");
RunTests();
Console.ReadLine();
}
static void RunTests()
{
Console.WriteLine("Today {1}: {0}", DateTime.Today.Date.GetFirstDayOfThisWeek(), DateTime.Today.Date.ToString("yyyy-MM-dd"));
Console.WriteLine("Saturday 2013-03-02: {0}", new DateTime(2013, 3, 2).GetFirstDayOfThisWeek());
Console.WriteLine("Sunday 2013-03-03: {0}", new DateTime(2013, 3, 3).GetFirstDayOfThisWeek());
Console.WriteLine("Monday 2013-03-04: {0}", new DateTime(2013, 3, 4).GetFirstDayOfThisWeek());
}
}

Modulo in C# works bad for -1 mod 7 (it should be 6, but C# returns -1)
so... a "one-liner" solution to this will look like this :)
private static DateTime GetFirstDayOfWeek(DateTime date)
{
return date.AddDays(
-(((int)date.DayOfWeek - 1) -
(int)Math.Floor((double)((int)date.DayOfWeek - 1) / 7) * 7));
}

I did it for Monday, but with similar logic for Sunday.
public static DateTime GetStartOfWeekDate()
{
// Get today's date
DateTime today = DateTime.Today;
// Get the value for today. DayOfWeek is an enum with 0 being Sunday, 1 Monday, etc
var todayDayOfWeek = (int)today.DayOfWeek;
var dateStartOfWeek = today;
// If today is not Monday, then get the date for Monday
if (todayDayOfWeek != 1)
{
// How many days to get back to Monday from today
var daysToStartOfWeek = (todayDayOfWeek - 1);
// Subtract from today's date the number of days to get to Monday
dateStartOfWeek = today.AddDays(-daysToStartOfWeek);
}
return dateStartOfWeek;
}

The following method should return the DateTime that you want. Pass in true for Sunday being the first day of the week, false for Monday:
private DateTime getStartOfWeek(bool useSunday)
{
DateTime now = DateTime.Now;
int dayOfWeek = (int)now.DayOfWeek;
if(!useSunday)
dayOfWeek--;
if(dayOfWeek < 0)
{// day of week is Sunday and we want to use Monday as the start of the week
// Sunday is now the seventh day of the week
dayOfWeek = 6;
}
return now.AddDays(-1 * (double)dayOfWeek);
}

You could use the excellent Umbrella library:
using nVentive.Umbrella.Extensions.Calendar;
DateTime beginning = DateTime.Now.BeginningOfWeek();
However, they do seem to have stored Monday as the first day of the week (see the property nVentive.Umbrella.Extensions.Calendar.DefaultDateTimeCalendarExtensions.WeekBeginsOn), so that previous localized solution is a bit better. Unfortunate.
Edit: looking closer at the question, it looks like Umbrella might actually work for that too:
// Or DateTime.Now.PreviousDay(DayOfWeek.Monday)
DateTime monday = DateTime.Now.PreviousMonday();
DateTime sunday = DateTime.Now.PreviousSunday();
Although it's worth noting that if you ask for the previous Monday on a Monday, it'll give you seven days back. But this is also true if you use BeginningOfWeek, which seems like a bug :(.

Following on from Compile This' answer, use the following method to obtain the date for any day of the week:
public static DateTime GetDayOfWeek(DateTime dateTime, DayOfWeek dayOfWeek)
{
var monday = dateTime.Date.AddDays((7 + (dateTime.DayOfWeek - DayOfWeek.Monday) % 7) * -1);
var diff = dayOfWeek - DayOfWeek.Monday;
if (diff == -1)
{
diff = 6;
}
return monday.AddDays(diff);
}

This will return both the beginning of the week and the end of the week dates:
private string[] GetWeekRange(DateTime dateToCheck)
{
string[] result = new string[2];
TimeSpan duration = new TimeSpan(0, 0, 0, 0); //One day
DateTime dateRangeBegin = dateToCheck;
DateTime dateRangeEnd = DateTime.Today.Add(duration);
dateRangeBegin = dateToCheck.AddDays(-(int)dateToCheck.DayOfWeek);
dateRangeEnd = dateToCheck.AddDays(6 - (int)dateToCheck.DayOfWeek);
result[0] = dateRangeBegin.Date.ToString();
result[1] = dateRangeEnd.Date.ToString();
return result;
}
I have posted the complete code for calculating the begin/end of week, month, quarter and year on my blog
ZamirsBlog

Calculating this way lets you choose which day of the week indicates the start of a new week (in the example I chose Monday).
Note that doing this calculation for a day that is a Monday will give the current Monday and not the previous one.
//Replace with whatever input date you want
DateTime inputDate = DateTime.Now;
//For this example, weeks start on Monday
int startOfWeek = (int)DayOfWeek.Monday;
//Calculate the number of days it has been since the start of the week
int daysSinceStartOfWeek = ((int)inputDate.DayOfWeek + 7 - startOfWeek) % 7;
DateTime previousStartOfWeek = inputDate.AddDays(-daysSinceStartOfWeek);

I work with a lot of schools, so correctly using Monday as the first day of the week is important here.
A lot of the most terse answers here don't work on Sunday -- we often end up returning the date of tomorrow on Sunday, which is not good for running a report on last week's activities.
Here's my solution, which returns last Monday on Sunday, and today on Monday.
// Adding 7 so remainder is always positive; Otherwise % returns -1 on Sunday.
var daysToSubtract = (7 + (int)today.DayOfWeek - (int)DayOfWeek.Monday) % 7;
var monday = today
.AddDays(-daysToSubtract)
.Date;
Remember to use a method parameter for "today" so it's unit testable!!

Here is a combination of a few of the answers. It uses an extension method that allows the culture to be passed in. If one is not passed in, the current culture is used. This will give it maximum flexibility and reuse.
/// <summary>
/// Gets the date of the first day of the week for the date.
/// </summary>
/// <param name="date">The date to be used</param>
/// <param name="cultureInfo">If none is provided, the current culture is used</param>
/// <returns>The date of the beggining of the week based on the culture specifed</returns>
public static DateTime StartOfWeek(this DateTime date, CultureInfo cultureInfo=null) =>
date.AddDays(-1 * (7 + (date.DayOfWeek - (cultureInfo ?? CultureInfo.CurrentCulture).DateTimeFormat.FirstDayOfWeek)) % 7).Date;
Example Usage:
public static void TestFirstDayOfWeekExtension() {
DateTime date = DateTime.Now;
foreach(System.Globalization.CultureInfo culture in CultureInfo.GetCultures(CultureTypes.UserCustomCulture | CultureTypes.SpecificCultures)) {
Console.WriteLine($"{culture.EnglishName}: {date.ToShortDateString()} First Day of week: {date.StartOfWeek(culture).ToShortDateString()}");
}
}

If you want Saturday or Sunday or any day of week, but not exceeding the current week (Sat-Sun), I got you covered with this piece of code.
public static DateTime GetDateInCurrentWeek(this DateTime date, DayOfWeek day)
{
var temp = date;
var limit = (int)date.DayOfWeek;
var returnDate = DateTime.MinValue;
if (date.DayOfWeek == day)
return date;
for (int i = limit; i < 6; i++)
{
temp = temp.AddDays(1);
if (day == temp.DayOfWeek)
{
returnDate = temp;
break;
}
}
if (returnDate == DateTime.MinValue)
{
for (int i = limit; i > -1; i++)
{
date = date.AddDays(-1);
if (day == date.DayOfWeek)
{
returnDate = date;
break;
}
}
}
return returnDate;
}

We like one-liners: Get the difference between the current culture's first day of week and the current day, and then subtract the number of days from the current day:
var weekStartDate = DateTime.Now.AddDays(-((int)now.DayOfWeek - (int)DateTimeFormatInfo.CurrentInfo.FirstDayOfWeek));

calculate difference between two dates using c#

I'm trying to calculate difference between two dates, my code is given below
DateTime daterenew = DateTime.Parse(drow.ItemArray.GetValue(16).ToString()); //18/01/2017
DateTime datecurrent = DateTime.Parse(DateTime.Now.ToString("dd/MM/yyyy"));
renewstatuslbl.Text = ((daterenew - datecurrent).Days) + " Day(s) remains";
But I'm getting an error
"String was not recognized as a valid DateTime."

I would simplify that:
var daterenew = DateTime.ParseExact("18/01/2017", "dd/MM/yyyy", CultureInfo.InvariantCulture);
var res = ((daterenew - DateTime.Today).Days) + " Day(s) remains";
Note, that DateTime.Now != DateTime.Today.

Try something like this
string dateString = drow.ItemArray.GetValue(16).ToString();
DateTime daterenew = DateTime.ParseExact(dateString, "dd/MM/yyyy", CultureInfo.InvariantCulture);
renewstatuslbl.Text = string.Format("{0} Day(s) remains", (daterenew - DateTime.Now).TotalDays);
Idea is in ParseExact where you can set up format for your date in drow.ItemArray
Also look at TotalDays

Assuming your drow.ItemArray.GetValue(16).ToString()format is always dd/MM/yyyy. Use ParseExact
DateTime daterenew = DateTime.ParseExact(drow.ItemArray.GetValue(16).ToString(), "dd/MM/yyyy", null); //18/01/2017
//DateTime datecurrent = DateTime.Parse(DateTime.Now.ToString("dd/MM/yyyy"));
DateTime datecurrent = DateTime.Now;
renewstatuslbl.Text = ((daterenew - datecurrent).Days) + " Day(s) remains";

The format of the date , causes the error. 18/01/2017
https://msdn.microsoft.com/en-us/library/az4se3k1(v=vs.110).aspx
example I used "yyyy/MM/dd"
//DateTime daterenew = DateTime.Parse("18/01/2017"); //18/01/2017
DateTime daterenew = DateTime.Parse("2017.01.18"); //18/01/2017
DateTime datecurrent = DateTime.Parse(DateTime.Now.ToString("dd/MM/yyyy"));
object renewstatuslbl = ((daterenew - datecurrent).Days) + " Day(s) remains";
thus, I think you can change the string date format first of the value before inserting to drow.ItemArray

enter codenamespace FineCalculation
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
DateTime date01 = date1.Value;
DateTime date02 = date2.Value;
TimeSpan timeSpan = date02 - date01;
int days = Convert.ToInt16(timeSpan.TotalDays);
double fine = 0;
if(days < 30)
{
fine = days * 0.5;
}else if(days > 30 && days < 60)
{
fine = days * 0.5 * 0.75;
}else if(days > 60)
{
fine = days * 0.5 * 0.75 * 1;
}
MessageBox.Show("For "+ days + " days fine is " + fine.ToString());
}
}
} here

How To Display Date In Locale For 0 Values?

Ok, so I have a date stored in UK format (dd/mm/yy) which I need to display in the locale of wherever the user might be.
The issue is that this date can be 000000 (00/00/2000); so I can't convert it to DateTime directly, as DateTime doesn't support 0 values for day or month.
I have this so far:
int dateInt = ddmmyy;
var year = (dateInt % 100) + 2000;
var month = (dateInt / 100) % 100;
var day = (dateInt / 100000);
var result = new DateTime(year, month, day); //2014/00/00 at this point, so breaks.
var resultStr = result.ToString(CultureInfo.InvariantCulture);
return resultStr;
What's the correct way to add support for 0 values initially? I've tried changing the 0 to 1 before converting to DateTime, running the conversion and then replacing with a 0 again; but due to culture variants I see no way that this method can support other cultures, which is the purpose of this conversion to begin with.
Any ideas? I'm guessing this is a common issue.

Is this what you need ?
using System;
namespace ConsoleApplication2
{
class Program
{
static void Main(string[] args)
{
int[] savedDates = new int[] { 000000, 010000, 000013 };
foreach (var item in savedDates)
{
DateTime date = ConvertToDate(item);
Console.WriteLine(item.ToString("D6") + " => " + date.ToShortDateString());
}
Console.ReadLine();
}
private static DateTime ConvertToDate(int item)
{
string temp = item.ToString("D6");
int day = int.Parse(temp.Substring(0, 2));
int month = int.Parse(temp.Substring(2, 2));
int year = int.Parse(temp.Substring(4, 2));
if (day == 0)
day = 1;
if (month == 0)
month = 1;
year += 2000;
return new DateTime(year, month, day);
}
}
}

I would not store dates like this as the methodology for doing so is already provided by the .NET framework.
The best way to store dates would be to use Culture.InvariantCulture for string conversion cases and then convert to local culture for display purposes as necessary. DateTime itself is culture-independent so converting between cultures is very easy.

Julian date string to DateTime

I am trying to convert Julian date string to DateTime but none of the solutions on the web seem to be working. I have a Julian date string 13324.
Julian Date: 13324
And I want to get the following DateTime
Date: 20-Nov-2013
Could you please direct me in the right direction. Thanks.

This is the simplest solution I can think of:
string julianDate = "13324";
int jDate = Convert.ToInt32(julianDate);
int day = jDate % 1000;
int year = (jDate - day) / 1000;
var date1 = new DateTime(year, 1, 1);
var result = date1.AddDays(day - 1);
(Note: this is all from memory; verify the syntax, etc.)

Sorry for my bad english
Try this code if the one on top didn't work. It worked for me.
public DateTime ConvertJulianToDatetime(string julianDate)
{
int dateint = int.Parse(julianDate);
DateTime dinicio = new DateTime(1840, 12, 31);
dinicio = dinicio.AddDays((double)dateint);
return dinicio;
}

This code is more reliable I think (can anyone notice):
public static DateTime FromJD(double JD)
{
return DateTime.FromOADate(JD - 2415018.5);
}
For MJD (modified julian day). Math.Floor or Math.Ceiling can be added as needed:
public static DateTime FromMJD(double MJD)
{
return DateTime.FromOADate((MJD - 2415018.5) + 2400000.5);
}
And one example for reverse translation:
public static double ToMJD(DateTime date)
{
return (date.ToOADate() + 2415018.5) -2400000.5;
}
public static double ToJD(DateTime date)
{
return date.ToOADate() + 2415018.5;
}

Safely adding/subtracting days to DateTime in C#

I have a function which takes two DateTime parameters and I have to add separate offsets to these date. I know that DateTime has a AddDays function to add days to a date and it throws an exception if DateTime is less than MinValue or greater than MaxValue.
Now I want to do a safe check whether adding/subtracting the following number of days to a DateTime can cause over/under flow or not.
safeStartDate = (startDate == DateTime.MinValue || startDate == DateTime.MaxValue) ? startDate : startDate.AddDays(startDateOffset);
safeEndDate = (endDate == DateTime.MaxValue || endDate == DateTime.MinValue) ? endDate : endDate.AddDays(enDateOffset);
By doing this, I am making it one level exception free but date can be DateTime.Max - 1 and while trying to add offset it throws an exception. I am looking a better way that whether the final values over/under flows without doing the actual calculation, in order to prevent exception.

If catch is not called very often you can do:
try
{
safeDate = dt.AddDays(days);
}
catch (ArgumentOutOfRangeException)
{
safeDate = date;
}
Alternatively,
var maxDays = (DateTime.MaxValue - dt).TotalDays;
safeDate = (days <= maxDays) ? dt.AddDays(days) : dt;
Or if there are negative days:
var maxDays = (DateTime.MaxValue - dt).TotalDays;
var minDays = (DateTime.MinValue - dt).TotalDays;
return (minDays <= days && days <= maxDays) ? dt.AddDays(days) : dt;
Or just use the method from Rawling's answer: CanAddDays(dt, days) ? dt.AddDays(days) : dt
The try/catch version is about 25% faster if you don't catch and about 1000x slower if you do. So, if you expected to catch more than about 1 time in every 5000 uses, then use the second version.

You can use the following to check whether you can add a given number of days to a given DateTime without causing an overflow:
bool CanAddDays(DateTime dt, int days)
{
double maxDaysToAdd = (DateTime.MaxValue - dt).TotalDays;
double minDaysToAdd = (DateTime.MinValue - dt).TotalDays;
return days <= maxDaysToAdd && days >= minDaysToAdd;
}

You might consider the following method:
private static DateTime AddDays(DateTime dateTime, int days)
{
var daysTimeSpanTicks = (new TimeSpan(days, 0, 0, 0)).Ticks;
return (days >= 0) ?
(DateTime.MaxValue.Ticks < dateTime.Ticks + daysTimeSpanTicks) ? dateTime : dateTime.AddDays(days) :
(dateTime.Ticks + daysTimeSpanTicks < 0) ? dateTime : dateTime.AddDays(days);
}
A sample usage is:
DateTime date = DateTime.MinValue;
DateTime safe = AddDays(date, -100);

I guess you are looking for something like this
DateTime Now = DateTime.Now;
DateTime Max = DateTime.MaxValue;
Max.Subtract(Now);
int DaysToAdd = 1000;//or something else
if (Max.Day > DaysToAdd) Now.AddDays(DaysToAdd);//add

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