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Problem with time intervals with given start time and end time c#

I am trying to develop a simple app for my upskill for c#, however I am stuck and new to the functionality of time with c#,
what I need:
I have a 3 text boxes that will contain start time, end time and time interval.
say user entered 7:00 AM , 12:00 PM , and 60 minutes it will store it inside a datatable and add it inside a listbox.
7:00 AM
8:00 AM
9:00 AM
10:00 AM
11:00 AM
12:00 AM
current approach:
I think I need to use the DateTime.AddMinutes(interval) but how am I going to arrive to the logic of it will stop if it reaches the end time? using the DateTime method? I am really confused on what to use, I saw TimeRange, TimeSpan etc.

You can use TimeSpan and DateTime together (to calculate and print respectively)
TimeSpan start = DateTime.Parse("7:00 AM").TimeOfDay;
TimeSpan end = DateTime.Parse("12:00 PM").TimeOfDay;
TimeSpan interval = new TimeSpan(0, 60, 0);
// If Start is bigger than end, Add a day to the end.
if (start > end)
end = end.Add(new TimeSpan(1, 0, 0, 0));
while (true)
{
Console.WriteLine((new DateTime() + start).ToString("hh:mm tt"));
start = start.Add(interval);
if (start > end)
break;
}
Output looks like this,
07:00 AM
08:00 AM
09:00 AM
10:00 AM
11:00 AM
12:00 PM
MS Documentation on TimeSpan

You can use TimeSpan with boolean logical operator to test if the currentTime is less than your endTime.
Below is example code.
TimeSpan startTime;
int interval;
TimeSpan tInterval = new TimeSpan(interval, 0, 0);
TimeSpan endTime;
TimeSpan currentTime = startTime;
while( (currentTime = startTime + tInterval) <= endTime)
{
// add currentTime to list box
}

This should take care of the issue with the End Times being "earlier" than the Start Time:
private static void TestTimeSpan()
{
int minutes = 60;
var interval = new TimeSpan(0,minutes,0);
TimeSpan start = DateTime.Parse("7:00 PM").TimeOfDay;
TimeSpan end = DateTime.Parse("1:00 AM").TimeOfDay;
//End of input data--start of solution
var diffSpan = end - start;
var diffMinutes = diffSpan.TotalMinutes > 0 ? diffSpan.TotalMinutes : diffSpan.TotalMinutes + (60 * 24);
var myTimeList = new List<TimeSpan>();
for(int i = 0; i < diffMinutes + minutes; i += minutes)
{
myTimeList.Add(start);
start = start.Add(interval);
}
myTimeList.ForEach(x => Console.WriteLine((new DateTime() + x).ToString("hh:mm tt")));
}
EDIT
Creating a sequence of Time values based in two input times and an interval is straight forward until the "start time" is earlier than the "end time", because just checking to see if the "end time" is greater than the start time fails your algorithm immediately.
This code utilizes the fact that there are only 24 hours in the day. Since the interval value is given in minutes, we can use that to section those minutes into "steps" of time. This code proceeds to step through each interval in time and capture the time at that step and save that in a List of TimeSpan (the captured value could easily be of type string--formatted as desired).
The trick here is when the "end time" is earlier than the "start time" we get a negative TimeSpan which is then used to calculate the steps to the "end time" on the next day. This is where the (60 * 24) [60 minutes x 24 hrs] part comes in to create the correct "diffMinutes" using a ternary operator.
After that the code simple iterates over the List "myTimeList" to write the formatted TimeSpan to the console. However, this 'List' is just a portable collection that can be sent anywhere in you code to do anything needed.
There are lots of other solutions, this one just seems straightforward, to me.

Minute give wrong values on substract

I want to subtract minutes and get the difference. below is my code
double diff = currBlock.EndTime.Subtract(currBlock.StartTime).TotalMinutes;
In given code (currBlock.StartTime = 23:30:00) and (currBlock.EndTime= 00:20:00)
here starttime is time of today i.e.(09/26/2016 23:30:00), night time which will be consider as 11:30 PM and endtime is time of tomorrow i.e.(09/27/2016 00:20:00), morning time which will be consider as 12:20 Am. In my code i am getting values in minus which is -1390 and it is incorrect. So please help me to solve this.
Here i have attach image of data for further reference.

please explain me properly, how do i use it? it is just a time block for different shift so there is no date include in it
There is a date included in it. You're telling us that EndTime is something like 09/27/2016 00:20:00, while StartTime is something like 09/26/2016 23:30:00. The problem is that that knowledge is in your head and not in your code. If you subtract the values as TimeSpans, then you're literally saying: what is 30 minutes minus 23 hours and 30 minutes. The answer, of course is -23 hours. To get the real difference, you must include the dates, which means utilizing a DateTime or DateTimeOffset type for both StartTime and EndTime, so you can encode that whole date and time. Then, when you do the subtraction, it will return the right value.

Below Code works for me. Thanks friends for your support and help.
string strCurrDate = (DateTime.Now.Date + currBlock.EndTime).ToString();
DateTime dtYourDate = DateTime.Parse((DateTime.Now.AddDays(-1).Date + currBlock.StartTime).ToString());
string strYourDate = dtYourDate.ToShortDateString() + " " + dtYourDate.ToLongTimeString();
string strTotalMinsElapsed = TotalMinutesElapsed(dtYourDate).ToString();
private long TotalMinutesElapsed(DateTime dtYourDate)
{
long lTotalMinutesElapsed = 0;
//Find Current Date and Time
DateTime dtCurrent = DateTime.Now;
//Find Time Difference details between current date and your given date
TimeSpan tsDiff = dtCurrent.Subtract(dtYourDate);
//Add Total Minutes for Days difference
lTotalMinutesElapsed = lTotalMinutesElapsed + tsDiff.Days * (24 * 60);
//Add Total Minutes for Hour difference
lTotalMinutesElapsed = lTotalMinutesElapsed + tsDiff.Hours * 60;
//Add Minutes
lTotalMinutesElapsed = lTotalMinutesElapsed + tsDiff.Minutes;
return lTotalMinutesElapsed;
}

Calculate the difference between two dates and times

I'm having problem in calculating the difference between two days using form in Visual Studio c#. I was trying to use TimeSpan but I want the messagebox to display a message. How to use if statement in this matter?
DateTime startDate = (DateTime)datePreviDate.Value;
DateTime endDate = (DateTime)datecurrentTime.Value;
TimeSpan ts = endDate.Subtract(startDate);
//Here i want to put if statemnet like
//if the difference of days are less than 2 AND PREVTIME + CURRENT TIME
//IS LESS THEN 24
//then MessageBox.Show.("you CANNOT CHANGE THE DATE")
//else MessageBox.Show.("you APPOINTMENT HAS BEEN CHANGED")
MessageBox.Show(ts.Days.ToString());
form image here

It's kind of hard to understand what you want. But this might help you. I am assuming "PREVTIME" and "CURRENTTIME" are assigned previously. I'm also just turning your comments into logic. Not sure if this is what you meant.
DateTime start = (DateTime)datePreviDate.Value;
DateTime end = (DateTime)datecurrentTime.Value;
var timespan = end - start
var totalTime = PREVTIME + CURRENTTIME;
if(timespan.TotalDays > 2 && totalTime < 24){
MessageBox.Show("You Cannot Change The Date");
//Continue Code Here
} else {
MessageBox.Show("Your Appointment Has Been Changed");
//Continue Code Here
}

How to find difference for two time values in string?

I am working on a new project in c#, i have no experience with date and time.
Here i need to find the difference between two time values which is in string format
string pointavalue = comboBox1.Text + ":" + comboBox2.Text + ":" + comboBox5.Text;
string pointbvalue = comboBox3.Text + ":" + comboBox4.Text + ":" + comboBox6.Text;
string pointcvalue = comboBox7.Text + ":" + comboBox8.Text + ":" + comboBox9.Text;
DateTime pointa = DateTime.Parse(pointavalue, System.Globalization.CultureInfo.CurrentCulture);
DateTime pointb = DateTime.Parse(pointbvalue, System.Globalization.CultureInfo.CurrentCulture);
DateTime pointc = DateTime.Parse(pointcvalue, System.Globalization.CultureInfo.CurrentCulture);
string time1 = pointa.ToString("HH:mm:ss");
string time2 = pointb.ToString("HH:mm:ss");
string time3 = pointc.ToString("HH:mm:ss");
There is three Values pointavalue, pointbvalue. pointcvalue.
They are combined string values of comboboxes.
Now how do i subtract pointbvalues from pointavalues?
I know they are in string format so operations cannot be performed.
the code you are looking is not mine, someone helped me but its working as a expected.
I am learning C# so bear with me.
ok i think figure out something, but still i can't solve it.
Here is my recent work with the code
DateTime inputa = DateTime.Parse(label21.Text, System.Globalization.CultureInfo.CurrentCulture);
DateTime inputb = DateTime.Parse(label23.Text, System.Globalization.CultureInfo.CurrentCulture);
if (pointa < pointb)
{
TimeSpan diff1 = pointb.Subtract(pointa);
DateTime d1=Convert.ToDateTime(diff1);
if (d1 < inputa)
{
label34.Text = "fail";
}
else
{
label34.Text = "pass";
}
Here i want to check the condition of the time diff1 and inputa, that's it that's all i need to finish this project.

The reason why you can't solve this problem is that you are trying to compare two different data types, Timespan and Datetime are not same
Either convert all your string to "Timespan" (That is better option).
Datetime will give you the present date, but it seems you don't need that.
Last but not least learn some basics before you ask these questions.

One more simple example:
void Main()
{
DateTime now = DateTime.Now;
DateTime yesterday = now.AddDays(-1);
TimeSpan difference = yesterday - now;
Console.WriteLine (difference.GetType().Name);
Console.WriteLine (difference.TotalSeconds); // expecting -86400
}
running this will print
TimeSpan
-86400

Take a look at the DateTime.Substract method:
TimeSpan abdiff = pointb.Substract(pointa);
TimeSpan bcdiff = pointc.Substract(pointb);
Alternatively, you can use the - operator, you get back a Timespan which contains the differences:
TimeSpan abdiff = pointb - pointa;
TimeSpan bcdiff = pointc - pointb;

Assuming that your combo boxes contain the hour, minute, and second then you could do the following.
TimeSpan pointa = new TimeSpan(int.Parse(comboBox1.Text), int.Parse(comboBox2.Text), int.Parse(comboBox5.Text));
TimeSpan pointb = new TimeSpan(int.Parse(comboBox3.Text), int.Parse(comboBox4.Text), int.Parse(comboBox6.Text));
TimeSpan pointc = new TimeSpan(int.Parse(comboBox7.Text), int.Parse(comboBox8.Text), int.Parse(comboBox9.Text));
TimeSpan aTob = pointa > pointb
? pointa - pointb
: (pointa + TimeSpan.FromDays(1)) - pointb;
Basically this assumes that your combo boxes only have valid hour (0-23), minute (0-59), and second (0-59) values. Then you just need to determine if your times are on the same day or not. If you assume that pointa is latter than pointb then checking if it is greater than pointb means you can do a straight subtraction. If not then it must be the time for the next day and you just add 1 day to it before subtracting pointb.
This is based on your assertion that 01:00 - 23:00 should be 2 hours and not -22. Thought it would be best if there where a date included so you would know for sure if the times are on the same day or the next day or from completely different years.

How to calculate when current pay period ends?

I want to know how to calculate the last date of this pay period?
I know that the pay is bi-weekly and the first period started on 01/09/2012.
so far here what i have done
DateTime d = new DateTime();
d = Convert.ToDateTime("01/09/2012");
while (d <= Convert.ToDateTime("01/06/2013")) {
PayPeriod.Items.Add(new ListItem(d.ToString("MM/dd/yyyy"), d.ToString("MM/dd/yyyy")));
d = d.Date.AddDays(14);
}
And this work perfect, but it work perfect because I have manually put the ending of the current pay period "01/06/2013".
My question is how can I automatically figure out the last date of the current pay period?

You can easily do this with the following logic:
DateTime startTime = new DateTime(2012,09,01);
DateTime now = DateTime.Now;
var diff = now.Subtract (startTime);
int daysToEndPeriod = diff.Days % 14;
if (daysToEndPeriod == 0)
Console.WriteLine("end of pay period");
else
Console.WriteLine("end of pay period is: " + DateTime.Now.AddDays(14-daysToEndPeriod).Date);
This works because you'll always get the Modulo operator returns how many days past the pay period you have left.