How to write JSON string value in code?

C# 10 and lower

I prefer this; just make sure you don't have a single quote in the string.

 var str = "{'Id':'123','DateOfRegistration':'2012-10-21T00:00:00+05:30','Status':0}"
              .Replace("'", "\"");

C# 11 and upper

It is still in preview mode, but you can simply place your json inside a pair of triple double-quote: """

var str = """
    {
        "Id": "123",
        "DateOfRegistration": "2012-10-21T00:00:00+05:30",
        "Status": 0
    }
""";

You have to do this

String str="{\"Id\":\"123\",\"DateOfRegistration\":\"2012-10-21T00:00:00+05:30\",\"Status\":0}";

Please see this for reference
Also from msdn :)

Short Notation  UTF-16 character    Description
\'  \u0027  allow to enter a ' in a character literal, e.g. '\''
\"  \u0022  allow to enter a " in a string literal, e.g. "this is the double quote (\") character"
\\  \u005c  allow to enter a \ character in a character or string literal, e.g. '\\' or "this is the backslash (\\) character"
\0  \u0000  allow to enter the character with code 0
\a  \u0007  alarm (usually the HW beep)
\b  \u0008  back-space
\f  \u000c  form-feed (next page)
\n  \u000a  line-feed (next line)
\r  \u000d  carriage-return (move to the beginning of the line)
\t  \u0009  (horizontal-) tab
\v  \u000b  vertical-tab

There is an alternate way to write these complex JSON using Expando object or XElement and then serialize.

https://blogs.msdn.microsoft.com/csharpfaq/2009/09/30/dynamic-in-c-4-0-introducing-the-expandoobject/

dynamic contact = new ExpandoObject
{    
    Name = "Patrick Hines",
    Phone = "206-555-0144",
    Address = new ExpandoObject
    {    
        Street = "123 Main St",
        City = "Mercer Island",
        State = "WA",    
        Postal = "68402"
    }
};

//Serialize to get Json string using NewtonSoft.JSON
string Json = JsonConvert.SerializeObject(contact);

Finetuning on sudhAnsu63's answer, this is a one-liner:

With .NET Core:

string str = JsonSerializer.Serialize(
  new {    
    Id = 2,
    DateOfRegistration = "2012-10-21T00:00:00+05:30",
    Status = 0
  }
);

With Json.NET:

string str = JsonConvert.SerializeObject(
  new {    
    Id = 2,
    DateOfRegistration = "2012-10-21T00:00:00+05:30",
    Status = 0
  }
);

There is no need to instantiate a dynamic ExpandoObject.