Add default value to an existing column based on If Then Else sql server 2008

Question

Is it possible to alter an existing column to accept a default value based on another column value?

For Eg:

Create table #Temp
(
    TempId int not n         


        

Answer 1

But a Check Constraint will just check your entries and not put a default value. This is my exact same problem. However, I researched that a Calculated Column will do the trick.