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Convert date and time into Correct format to compare to current date

I have a date in this format "2017-03-29" and time like "09:30", How do I conver toDatetime.
Following is how I have
string date = "2017-03-29";
string time = "09:30"
I need to convert this to DateTime in c#.
I also need to compare this converted DateTime with current dateTime, I will be using this in comparison in Linq

Use DateTime.ParseExact. Also your problem statement and code shown have nothing to do with Linq. The code below assumes the hours are in 24 hour format, adjust accordingly if that is not the case and provide an am/pm flag.
string date = "2017-03-29";
string time = "09:30";
var dateTime = DateTime.ParseExact(date+time, "yyyy-MM-ddHH:mm", null);

I would say the same as #Sam, but I don't have enough reputation to comment.
string date = "2017-03-29";
string time = "09:30";
string dateTimeString = string.Format("{0} {1}", date, time);
DateTime dateTime = DateTime.ParseExact(dateTimeString, "yyyy-MM-dd HH:mm", CultureInfo.InvariantCulture);
Note that the Kind of the resulting DateTime is DateTimeKind.Unspecified. Convert it as necessary.

Using the variables provided:
string dateTime = date + " " + time;
DateTime d = Convert.ToDateTime(dateTime);

DateTime parsing - unexpected result

I have datetime string
dateStr = "2017-03-21T23:00:00.000Z";
then I am calling
var date = DateTime.Parse(dateStr);
and unexpectedly my date equals
22.03.2017 00:00:00
I expected it to be 21.03.2017
What's going on here?

DateTime.Parse() is locale specific and will take into account your local time zone when parsing dates.
If you are in CET (Central European Time) during the winter your offset is one hour ahead of UTC. The date given is marked with a Z indicating it is in UTC, so DateTime.Parse() will adjust that to your local timezone.
There is an override that allows you to change that behaviour if you want, by specifying a specific DateTimeStyles enum. DateTimeStyles.AdjustToUniversal is what you are looking for as that should keep the DateTime as UTC.
And if you only want the date part afterwards, you can just call .Date on the DateTime object you got back from Parse()
So, something like this:
var date = DateTime.Parse(dateStr, CultureInfo.InvariantCulture, DateTimeStyles.AdjustToUniversal).Date;

if the date format does not change then you can use the below code to get date part from date string. But it is a bit risky due to its strict dependency on the input format.
string dateStr = "2017-03-21T23:00:00.000Z";
int year = Int32.Parse(dateStr.Substring(0, 4));
int month = Int32.Parse(dateStr.Substring(5, 2));
int day = Int32.Parse(dateStr.Substring(8, 2));
var date = new DateTime(year, month, day);
Console.WriteLine(date);

Because the format of type 'DateTime' variable is 'YYYY-MM-DD hh:mm:ss'.
If you run this code:
var dt = DateTime.Now;
Console.WriteLine(dt);
You'll see '24/03/2017 12:54:47'
If you have 'YYYY-MM-DD' format, add .ToString("dd-MM-yyyy"), then:
string dateStr = "2017-03-21T23:00:00.000Z";
var date = DateTime.Parse(dateStr).ToString("dd-MM-yyyy");
Result:'24-03-2017'

Assign value of a string (containing date and time) to two different variable (one for Date and one for Time)

I have a string ("CompletionDate") which contains the value "2/28/2017 5:24:00 PM"
Now I have 2 variables (EDate and ETime). I want to assign the Date to EDate (i.e 2/28/2017) and Time to ETime (i.e. 5:24:00 PM).
How can I split the Date and Time from a single string.
Kindly Help.
My approach right now is like :
string CompletionDate = string.Empty;
string ProjectEDate = string.Empty;
string ProjectETime = string.Empty;
CompletionDate = "2017-03-29 12:58:00";
DateTime dt = DateTime.ParseExact(CompletionDate, "yyyy-MM-dd", CultureInfo.CreateSpecificCulture("en-us"));
DateTime dt1 = DateTime.ParseExact(CompletionDate, "HH:mm:ss", CultureInfo.CreateSpecificCulture("en-us"));
var ProjectEDate = dt.ToString();
var ProjectETime = dt1.ToString();
But its throwing exception that string is not in correct format. Kindly help

#Chris pointed one of your problems, but you have one more. You are passing full date time string and trying to treat it as date or time only, which is not true. Instead I suggest you to parse DateTime object with both date and time, and then take whatever you need from parsed object:
CultureInfo enUS = CultureInfo.CreateSpecificCulture("en-us");
DateTime dt = DateTime.ParseExact(CompletionDate, "yyyy-MM-dd HH:mm:ss", enUS);
var ProjectEDate = dt.Date.ToString();
var ProjectETime = dt.TimeOfDay.ToString();

You need to specify the full format as same as the input string to parse method.
DateTime dt = DateTime.ParseExact(CompletionDate, "yyyy-MM-dd HH:mm:ss", System.Globalization.CultureInfo.CreateSpecificCulture("en-us"));
To get results you can use below methods available by default in DateTime.
dt.ToShortTimeString()
"12:58 PM"
dt.ToLongTimeString()
"12:58:00 PM"
dt.ToLongDateString()
"Wednesday, March 29, 2017"
dt.ToShortDateString()
"3/29/2017"
Or you can specify the format to ToString method.
dt.ToString("yyyy-MM-dd")
"2017-03-29"
dt.ToString("HH:mm:ss")
"12:58:00"

DateTime.ParseExact(CompletionDate, "yyy-MM-dd", ...
You are missing 4th 'y' in date format string:
"yyyy-MM-dd"
^
here
and:
String was not recognized as a valid DateTime " format dd/MM/yyyy"

Why do you parse into DateTime and then convert to a string using ToString again? Couldn´t you just simply use String.Split when all you want is to split the time from the day and you know the exact format?
var CompletionDate = "2017-03-29 12:58:00";
var tmp = CompletionDate.Split(' ');
var ProjectEDate = tmp[0];
var ProjectETime = tmp[1];

Get yesterday's date from the date entered

I have console application that accepts date as parameter. However, the date is passed as a string in this format:
string dt = DateTime.Now.ToString("yyyyMMdd");
Once the date is entered I need to programmatically get day - 1 from the entered date. Since this is a string, I cannot do any calculation.
For example, user enters:
20141023
I need to subtract a day from the date to get:
20141022
I did a quick fix to solve my immediate need, however, this is not the right way to do it and it has a bug:
int yt = Int32.Parse(dt) - 1;
And then I turn around and convert it yt.ToString()
The above solution will not work if it's the 1st of the month.
Is there a way I can programmatically get yesterday's date in the format (yyyyMMdd) without changing the format and possibly not using the TimeSpan?

Why don't parse the input into a DateTime object? Then you can use the DateTime.AddDays(-1)
For example:
var inputDate = DateTime.ParseExact("20141022", "yyyyMMdd", CultureInfo.InvariantCulture); // change "20141022" into the inputted value
var yesterday = inputDate.AddDays(-1);
var yesterdayString = yesterday.ToString("yyyyMMdd"); // this will be yesterdays date, in the string format

Try this...
DateTime data = DateTime.ParseExact("20141023", "yyyyMMdd", CultureInfo.InvariantCulture);
Console.WriteLine("{0} - {1}", data, data.AddDays(-1).ToString("yyyyMMdd"));

Would this work for you ?
string newDateTimeStr = (DateTime.Today.AddDays(-1)).ToString("yyyyMMdd");
EDIT:
for the date entered by the user:
string txtInputDate = Console.ReadLine();
DateTime dateTime = new DateTime(txtInputDate).ToLocalTime();
string newDateTimeStr = (dateTime.AddDays(-1)).ToString("yyyyMMdd");

How to convert dd/mm to Mysql Datetime format in c#

I have a date string with dd/mm format like 06/03.Now i have to store this string into mysql table column with DATETIME format.
I am getting the problem as How can i add the current year generically because i don't want to hard code it.Subsequently how will i convert it into MySql DATETIME format for saving it.
Please help me .

You can use Parse method of DateTime:
DateTime dateTime = DateTime.Parse("06/03");
UPDATE
For your comment:
Also after parsing into DateTime i am getting date correct but time i
dont want to be 12:00:00 AM instead i want it to be 00:00:00.
12:00:00 AM corresponds to 00:00:00 only. You can verify that by getting Hour property which will return 0 and also TimeOfDay will too return 00:00:00.
Even if you try to parse exact date, it also creates the same format.
DateTime dateTime = DateTime.ParseExact("06/03 00:00:00", "dd/MM hh:mm:ss",
CultureInfo.InvariantCulture);
And you don't need conversion from DateTime object to SQL compliant DateTime object. You can pass the .Net object to SQL writer.

Consider the code:
C#
string s = "06/03";
System.DateTime dateNow = Convert.ToDateTime(s);
will give the output as you required
in VB.Net :
Dim s As String = "06/03"
Dim dateNow As Date = CDate(s)
MsgBox(dateNow)

You could do something like
var some_date = "06/03";
var year = DateTime.Now.Year;
var option = some_date+"/"+year;
Or use any of the string formats to bend it to your needs
More on date string format can be found on this MSDN page.
Edit:
If you want zeroes in the time, like your comment said, you can usit Rohit vats answer and do:
DateTime dateTime = DateTime.Parse("06/03");
var s1 = dateTime.ToString("MM/dd/yy 00:00:00");
// Output: 03/06/14 00:00:00
var s2 = dateTime.ToString("MM/dd/yyyy 00:00:00");
// Output: 03/06/2014 00:00:00