Datetime in C# Add Days

Datetime in C# add days

DateTime is immutable. That means you cannot change it's state and have to assign the result of an operation to a variable.

endDate = endDate.AddDays(addedDays);

Adding days to a DateTime in C#

Do you want to add days?

DateTime newDate = DateTime.Today.AddDays(10);

Note that you get a new DateTime back!

MSDN

C# Datetime add days with hours and minutes

Use DateTime.Now instead of DateTime.Today

DateTime.Now is not dirty, and formatting it is not either

DateTime.Now gives you a DateTime variable.

The formatting .ToString() returns a string to format as you wish.

How can I add a day to a DateTime in a specific timezone

Here are extension methods that you can use for this.

First, this AddDays method matches the signature you were asking about. It operates on DateTime values:

public static DateTime AddDays(this DateTime dt, double days, TimeZoneInfo tz)
{
    // If the kind is Local or Utc, convert that point in time to the given time zone
    DateTimeKind originalKind = dt.Kind;
    if (originalKind != DateTimeKind.Unspecified)
    {
        dt = TimeZoneInfo.ConvertTime(dt, tz);
    }

    // Add days with respect to the wall time only
    DateTime added = dt.AddDays(days);

    // Resolve the added value to a specific point in time
    DateTimeOffset resolved = added.ToDateTimeOffset(tz);

    // Return only the DateTime portion, but take the original kind into account
    switch (originalKind)
    {
        case DateTimeKind.Local:
            return resolved.LocalDateTime;
        case DateTimeKind.Utc:
            return resolved.UtcDateTime;
        default: // DateTimeKind.Unspecified
            return resolved.DateTime;
    }
}

Here is another variation of that extension method. This one operates on DateTimeOffset values:

public static DateTimeOffset AddDays(this DateTimeOffset dto, double days, TimeZoneInfo tz)
{
    // Make sure the input time is in the provided time zone
    dto = TimeZoneInfo.ConvertTime(dto, tz);

    // Add days with respect to the wall time only
    DateTime added = dto.DateTime.AddDays(days);

    // Resolve the added value to a specific point in time
    DateTimeOffset resolved = added.ToDateTimeOffset(tz);

    // Return the fully resolved value
    return resolved;
}

Both of the above methods depend on the following ToDateTimeOffset extension method (which I've used in a few different posts now).

public static DateTimeOffset ToDateTimeOffset(this DateTime dt, TimeZoneInfo tz)
{
    if (dt.Kind != DateTimeKind.Unspecified)
    {
        // Handle UTC or Local kinds (regular and hidden 4th kind)
        DateTimeOffset dto = new DateTimeOffset(dt.ToUniversalTime(), TimeSpan.Zero);
        return TimeZoneInfo.ConvertTime(dto, tz);
    }

    if (tz.IsAmbiguousTime(dt))
    {
        // Prefer the daylight offset, because it comes first sequentially (1:30 ET becomes 1:30 EDT)
        TimeSpan[] offsets = tz.GetAmbiguousTimeOffsets(dt);
        TimeSpan offset = offsets[0] > offsets[1] ? offsets[0] : offsets[1];
        return new DateTimeOffset(dt, offset);
    }

    if (tz.IsInvalidTime(dt))
    {
        // Advance by the gap, and return with the daylight offset  (2:30 ET becomes 3:30 EDT)
        TimeSpan[] offsets = { tz.GetUtcOffset(dt.AddDays(-1)), tz.GetUtcOffset(dt.AddDays(1)) };
        TimeSpan gap = offsets[1] - offsets[0];
        return new DateTimeOffset(dt.Add(gap), offsets[1]);
    }

    // Simple case
    return new DateTimeOffset(dt, tz.GetUtcOffset(dt));
}

Lastly, I'll point out that there is another option to consider: Use the Noda Time library. It's ZoneDateTime.Add method has exactly this purpose.

How to add day to DateTime at end of month?

var ldUserEndTime = DateTime.Today + new TimeSpan(1, 0, 45, 0);

How to add days to a date and pass the sum to an inputdate in c #?

The following code snippet contains two InputDate components. When you select a date in the first one, the date in the second one changed to the selected date in the first component plus 45 days.

    @page "/"

<EditForm EditContext="EditContext" OnValidSubmit="HandleValidSubmit">
    <DataAnnotationsValidator />

    <InputDate placeholder="Arrival Date" @bind-Value="person.ArrivalDate"
               @oninput="AddDays" />
    <InputDate placeholder="Departure Date" @bind-Value="person.DepartureDate" />
    <ValidationMessage For="@(() => person.ArrivalDate)" />
    <ValidationMessage For="@(() => person.DepartureDate)" />

    <p><button type="submit">Submit</button></p>
</EditForm>

@code {

    private Person person = new Person();
    EditContext EditContext;

    protected override void OnInitialized()
    {
        EditContext = new EditContext(person);
        base.OnInitialized();
    }

    private async Task AddDays(ChangeEventArgs args)
    {
        person.DepartureDate = Convert.ToDateTime(args.Value).AddDays(45);
        await Task.CompletedTask;
    }

    void HandleValidSubmit()
    {
        Console.WriteLine("TODO: Actually do something with the valid data");
    }

    public class Person
    {
        public DateTime ArrivalDate { get; set; } = DateTime.Now;
        public DateTime DepartureDate { get; set; } = DateTime.Now;

    }
}

Hope this helps...

DateTime.AddDays what value to pass to generate an exception

If you pass in int.MaxValue, that should end up with a value which is outside the representable range for DateTime, whatever the original DateTime is.

Sample code, tested on csharppad.com:

DateTime.MinValue.AddDays(int.MaxValue);

Using Assert.Fail in a finally block is a mistake though... that will always be called. It's not clear what your test framework is, but I'd expect something like:

Assert.Throws<ArgumentOutOfRangeException>(() => /* code here */);

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