Develop Reference

Change the time forward

I am getting dates from the database and for each date I want to change the time forward starting from the DateTime that was obtained from the database until I get to a given Fixed Time (Y). However, (Y) might be in the next day.
For example if the date from the database is [7/6/2017 5:00:00 AM] and the given Fixed Time is 10:00 PM then I want to get [7/6/2017 10:00:00 PM].
However if the fixed time is 02:00 AM then I want to get [7/7/2017 02:00:00 AM] (notice that the date has increased by one)
Note: The code is running, but I modified the code to make it shorter and make more sense. Thus, there might be syntax or spelling mistakes.
My first solution was something like this:
private DateTime setTimeForeward(DateTime date) {
DateTime today = DateTime.ParseExact(FixedTime, "hh:mm tt", CultureInfo.InvariantCulture);
TimeSpan difference = today.TimeOfDay - date.TimeOfDay;
return date + difference;
}
That didn't work as expected when the fixed time is 02:00 AM. The difference becomes negative( it doesn't go around the clock) and the date will be [7/6/2017 02:00:00 AM].
I ended up with the following code
private DateTime setTimeForeward(DateTime date) {
DateTime today = DateTime.ParseExact(FixedTime "hh:mm tt", CultureInfo.InvariantCulture);
TimeSpan difference = today.TimeOfDay - date.TimeOfDay;
if (difference.Hours < 0) {
difference += new TimeSpan(24, 0, 0);
}
return date + difference;
}
I am not sure if my function is logically correct and I feel like I am overthinking it. Also,I am not sure if there's a better way or a built in function that does what I want for me. Basically, I am looking for a correct and an elegant solution.
Thank you very much in advanced.

In this method, I'm using DateTime fixedTime to represent a time. I don't really care about it's Day, Month, and Year values.
static DateTime GetClosingTime(DateTime fixedTime, DateTime dbTime)
{
var cutoff = new DateTime(dbTime.Year, dbTime.Month, dbTime.Day, fixedTime.Hour, fixedTime.Minute, fixedTime.Second);
if (dbTime < cutoff)
return cutoff;
else
{
cutoff = cutoff.AddDays(1);
return cutoff;
}
}
Here's calling it with your provided example input.
var FixedTime10PM = new DateTime(1, 1, 1, 22, 0, 0);
var FixedTime02AM = new DateTime(1, 1, 1, 2, 0, 0);
var dbTime = new DateTime(2018, 6, 20, 5, 0, 0);
var dt1 = GetClosingTime(FixedTime10PM, dbTime);
var dt2 = GetClosingTime(FixedTime02AM, dbTime);
Console.WriteLine(dt1.ToLongDateString() + " " + dt1.ToLongTimeString());
Console.WriteLine(dt2.ToLongDateString() + " " + dt2.ToLongTimeString());
And here's my output:
EDIT:
Simplified method based on suggestions in comments:
static DateTime GetClosingTime(DateTime fixedTime, DateTime dbTime)
{
var cutoff = new DateTime(dbTime.Year, dbTime.Month, dbTime.Day, fixedTime.Hour, fixedTime.Minute, fixedTime.Second);
return dbTime < cutoff ? cutoff : cutoff.AddDays(1);
}

Your logic is almost right but you shouldn't be checking for difference.Hours because there might be a difference in minutes (or even seconds if you changed the format later).
I adjusted your function and changed some variable names to make them easier to follow:
private DateTime SetTimeForward(DateTime originalDate)
{
TimeSpan newTime = DateTime.ParseExact(FixedTime,
"hh:mm tt",
CultureInfo.InvariantCulture).TimeOfDay;
TimeSpan diff = newTime - originalDate.TimeOfDay;
if (diff.Ticks < 0)
diff = diff.Add(new TimeSpan(24, 0, 0));
return originalDate.Add(diff);
}
Some remarks:
If your FixedTime is really fixed, you might want to store it directly as a TimeSpan so you don't have to parse it every time.
If you parse the FixedTime because it's changeable, you might pass it as a second argument instead:
private DateTime SetTimeForward(DateTime originalDate, string fixedTime)
Or:
private DateTime SetTimeForward(DateTime originalDate, TimeSpan newTime)
The current implementation does not change the date value if the newTime is equal to originalDate.TimeOfDay. I.E., If the originalDate is 7/6/2017 2:00 AM and the FixedTime/newTime is 02:00 AM, the returned date will be equal to the originalDate. If that's not your desired behavior, you might change diff.Ticks < 0 to diff.Ticks <= 0.

Slightly different approach:
private DateTime setTimeForeward(DateTime date)
{
var targetTimeOfDay = TimeSpan.ParseExact(FixedTime, "hh:mm tt", CultureInfo.InvariantCulture);
if (targetTimeOfDay < date.TimeOfDay)
{
date = date.AddDays(1);
}
return date.Date + targetTimeOfDay;
}
I'm getting target time as TimeSpan from the beginning instead of creating DateTime and getting TimeOfDay (which is TimeSpan).
Then I check if the target time of day is lower than time to be modified and if it is I add one day.
I use date.Date + targetTimeOfDay as return value as date.Date will return date with time set to 00:00 and adding target time to it will already set the target hour without calculating the difference.

C# time subtraction Issue

I have been facing issue on time subtraction in C#.
For example I start timer on 4/5/2017 11:56:27 PM and end the timer in 5/5/2017 12:10:27 AM when I subtract this it shows me result 23 hours.
I want that it show exact time like 14 minutes. I am sharing my code as well.
double rate1 = Convert.ToDouble(rate.Text);
double value = rate1 / 3600;
DateTime dt = DateTime.Parse(text3.Text);
DateTime edt = DateTime.Parse(text5.Text);
var res = dt.Subtract(edt).ToString().Replace('-', ' ');
DateTime tt = Convert.ToDateTime(res);
DateTime dt1 = DateTime.Parse(text4.Text);
DateTime edt1 = DateTime.Parse(text6.Text);
var res1 = dt.Subtract(edt1).ToString().Replace('-', ' ');
double sec = TimeSpan.Parse(res).TotalSeconds;
double sec1 = TimeSpan.Parse(res1).TotalSeconds;
text7.Text = res.ToString();
text8.Text = res1.ToString();

It seems like you're showing a lot of code that's difficult to reproduce for us, and the variable names are not the clearest. I'm assuming dt stands for "datetime", and edt stands for "end datetime". If that's correct, then you're subtracting the end date from the start date instead of the other way around (you should subtract the smaller from the larger).
So, here's how to get the difference between start and end (I'm using Hindi culture info for this):
var dateFormatCulture = new CultureInfo("hi-IN");
var startDate = DateTime.Parse("4/5/2017 11:56:27 PM", dateFormatCulture);
var endDate = DateTime.Parse("5/5/2017 12:10:27 AM", dateFormatCulture);
var difference = endDate.Subtract(startDate);
You say you want "the exact time like 14 minutes". I'm not sure if that means you don't want to show the rest of the values, but here are a few ways you can display it.
Console.WriteLine($"General short string format: {difference:g}");
Console.WriteLine(
"Custom string format: {0} days, {1} hours, {2} minutes, {3} seconds",
difference.Days, difference.Hours, difference.Minutes, difference.Seconds);
Console.WriteLine("In terms of minutes, the total minutes difference is: {0}",
difference.TotalMinutes);
Notice that there's a difference between the second an third example in the methods being called to show the minutes . Minutes will display just the minutes portion of the difference. TotalMinutes will display the entire difference in terms of minutes. In your case they are the same, but if the difference was 1 hour and 14 minutes, Minutes would still be 14, but TotalMinutes would be 74.
The output looks like:

It looks like you might have a copy/paste error. In this line, did you mean to reference dt1 rather than dt?
var res1 = dt.Subtract(edt1).ToString().Replace('-', ' ');

How to divide time range in intervals if Start Time is greater than End time

I'm accepting time range from user in a 24 hr clock format.My code below works if the start time is less than End time. The following code divides the given time range with the interval.
How should I deal with a situation where Start Time is less than End Time. E.g. If Start Time is say 21:00 (9 PM) and End time is 03:00 (3 AM). Any idea how should I divide the time range where Start time is MORE than End Time?
DateTime start = DateTime.ParseExact(txtStartTime.Text.Trim(),"HH:mm", null);
DateTime end = DateTime.ParseExact(txtEndTime.Text.Trim(), "HH:mm", null);
int interval = Convert.ToInt32(txtSessionDuration.Text.Trim());
for (DateTime i = start; i < end; i = i.AddMinutes(interval))
{
//some code goes here...
}

Assuming that there is no user error and user want to get intervals, when end time is less than start time.
As DateTime contains not only time component, but date component, so we can simply add one day if end time is less than start time. You should modify you code as follows:
DateTime start = DateTime.ParseExact(txtStartTime.Text.Trim(),"HH:mm", null);
DateTime end = DateTime.ParseExact(txtEndTime.Text.Trim(), "HH:mm", null);
if (end < start)
{
end = end.AddDays(1);
}
int interval = Convert.ToInt32(txtSessionDuration.Text.Trim());
for (DateTime i = start; i < end; i = i.AddMinutes(interval))
{
//some code goes here...
}
After you have parsed DateTime from string - both start and end contains equals date component. This mean that end time is earlier than start time. But if you passing end time, that is less than start time, you actually mean, that end time is time of next day.
So, if time component of end is less than it of start you can simply add 1 day to end and you will have ability to iterate from start to end.

How should I deal with a situation where Start Time is less than End
Time?
Don't you can compare theirs .TimeOfDay properties? Like;
if(start.TimeOfDay < end.TimeOfDay)
Or instead of that, you can parse them to TimeSpan and compare directly.

You can do by
DateTime start = DateTime.ParseExact(DateTime.Now().ToString("dd/MM/yyyy") + txtStartTime.Text.Trim(),"dd/MM/yyyy HH:mm", null);
DateTime end = DateTime.ParseExact(DateTime.Now().ToString("dd/MM/yyyy") + txtEndTime.Text.Trim(), "dd/MM/yyyy HH:mm", null);
if(start.TimeOfDay < end.TimeOfDay)
{
// do stuff here
}

Use timespan:
DateTime departure = new DateTime(2010, 6, 12, 18, 32, 0);
DateTime arrival = new DateTime(2010, 6, 13, 22, 47, 0);
TimeSpan travelTime = arrival - departure;
Console.WriteLine("{0} - {1} = {2}", arrival, departure, travelTime);
// The example displays the following output:
// 6/13/2010 10:47:00 PM - 6/12/2010 6:32:00 PM = 1.04:15:00
reference: https://msdn.microsoft.com/en-us/library/system.timespan(v=vs.110).aspx

Date comparison - How to check if 20 minutes have passed?

How to check if 20 minutes have passed from current date?
For example:
var start = DateTime.Now;
var oldDate = "08/10/2011 23:50:31";
if(start ??) {
//20 minutes were passed from start
}
what's the best way to do this?
Thanks :)

You should convert your start time to a UTC time, say 'start'.
You can now compare your start time to the current UTC time using:
DateTime.UtcNow > start.AddMinutes(20)
This approach means that you will get the correct answer around daylight savings time changes.
By adding time to the start time instead of subtracting and comparing the total time on a TimeSpan you have a more readable syntax AND you can handle more date difference cases, e.g. 1 month from the start, 2 weeks from the start, ...

var start = DateTime.Now;
var oldDate = DateTime.Parse("08/10/2011 23:50:31");
if ((start - oldDate).TotalMinutes >= 20)
{
//20 minutes were passed from start
}

var start = DateTime.Now;
var oldDate = DateTime.Parse("08/10/2011 23:50:31");
if(start.Subtract(oldDate) >= TimeSpan.FromMinutes(20))
{
//20 minutes were passed from start
}

Parse oldDate into a DateTime object (DateTime.Parse).
Subtract the parsed date from start. This will return a TimeSpan.
Inspect TotalMinutes.

I was able to accomplish this by using a JodaTime Library in my project. I came out with this code.
String datetime1 = "2012/08/24 05:22:34";
String datetime2 = "2012/08/24 05:23:28";
DateTimeFormatter format = DateTimeFormat.forPattern("yyyy/MM/dd HH:mm:ss");
DateTime time1 = format.parseDateTime(datetime1);
DateTime time2 = format.parseDateTime(datetime2);
Minutes Interval = Minutes.minutesBetween(time1, time2);
Minutes minInterval = Minutes.minutes(20);
if(Interval.isGreaterThan(minInterval)){
return true;
}
else{
return false;
}
This will check if the Time Interval between datetime1 and datetime2 is GreaterThan 20 Minutes. Change the property to Seconds. It will be easier for you know. This will return false.

var end = DateTime.Parse(oldDate);
if (start.Hour == end.Hour && start.AddMinutes(20).Minute >= end.Minute)

How to Round to the Nearest 0.5?

in my application
Ex 1: Start time 12.30
(-)End time 16.00 here i get the value as 3.7 but i need to show this 3.7 as 3.5 in my application
Ex 2: Start time 12.00
(-)End time 16.00 here i get the value as 4.0 here there is no need to alter the value
(1.7,2.7,3.7,4.7,.... etc ) as to be represented as(1.5,2.5,3.5,4.5,.. etc )
so how to write an function for this where if the vale contains(1.7,2.7) i should change to 1.5,2.5
or if it contains 1.0,2.0 then there is no need to replace any value?

This extension method ought to do the job:
public decimal RoundToNearestHalf(this decimal value)
{
return Math.Round(value * 2) / 2;
}
var num1 = (3.7).RoundToNearestHalf(); // 3.5
var num1 = (4.0).RoundToNearestHalf(); // 4.0
I've used the decimal type in the code because it seems you want to maintain base 10 precision. If you don't, then float/double would do just as well, of course.

Use the DateTime type. Subtracting DateTime types returns a TimeSpan. Use TimeSpan.TotalHours to get your result. E.g.:-
var x = DateTime.Parse("12:30");
var y = DateTime.Parse("16:00");
Console.WriteLine((y - x).TotalHours);

Use DateTime type to work with time. Example:
string time1 = "12:30";
string time2 = "16:00";
TimeSpan diff = DateTime.Parse(time2)-DateTime.Parse(time2);
string diffString = diff.ToString("hh:mm"); // will be 03:30

Multiply hours with 60 and add minutes. You'll get total number of minutes.
12hours and 30 minutes = 720 + 30 = 750 minutes.
16 hours = 960 minutes.
Subtract the first value from the other and divide it by 60
(960 - 750) / 60 = 210 / 60 = 3.5

You should use TimeSpan and round it off:
TimeSpan startTime = new TimeSpan(12, 30, 0);
TimeSpan endTime = new TimeSpan(16, 0, 0);
TimeSpan span = endTime - startTime;
double totalHours = span.TotalHours;
double roundedToHalf = Math.Round(totalHours * 2) / 2;
Console.WriteLine(roundedToHalf);
UPDATE:
If the start and end time are from different dates, you should use DateTime for startTime and endTime.

If the values in your question represent times you can't do decimal arithmetic with them and expect time values as results.
You need to manipulate the values as times
I don't know C#, but it must have some time functions.

Have the times as DateTime then use Timspan to find the difference between the two times?

Times are not integers or floats. You can't work with them as if they are - you wouldn't try to do integer math using the String class, would you?
DateTime and TimeSpan are you friends for this kind of data manipulation.

You can use the C# Floor and Ceil method of the Math Class. Read more about it in the below URLs:
http://msdn.microsoft.com/en-us/library/system.math.ceiling(VS.71).aspx
http://dotnetperls.com/math-floor

string i = "2.0";
if (i == "2.3" || i == "3.3" || i == "4.3")
{
string strReplace = i.Replace(".3", ".5");
}
else
{
string strReplace = i;
}