assigning a value for instead of null

I don't think you can escape from if, but you can use the shorthand syntax for it:

// maybeNull is the passed parameter - if it's not null it will be assigned to someVariable, else use valueToAssignIfNull
var someVariable = maybeNull ?? valueToAssignIfNull;

I am no c# pro but I'd try:

RADentryDate.SelectedDate = !DBNull.Value.Equals(row[15]) ? DateTime.Parse(row[15].ToString()) : DateTime.Now;

The solution is pretty simple as solution 2 says,

you may use null coal-easing operator (??) here.

Write something like this to assign default value, if current value comes null.
(??) operator will allow you to assign default value if it comes null and takes it self if it is not null.

RADentryDate.SelectedDate = DateTime.Parse(row[15] ?? DateTime.Now);

Is this an answer to your problem?

Thanks :)

Easiest way....
You have to declare the variable in the following manner:

string variableName = "";

And you're through!!.

;-)

well you can use below line instead of if-else ...

(Control_id.value=null) ? return "Your value" : return Control_id.value

or you can use method given by Michael,

(Control_id.Equals(null))? return "the value you want" : return Control_id.Value

Above method is called Ternary operator {"Condition ? Result1 : Result2"}