C# ?? and ??= operators Edit
?? is a C# Null-Collation operator is a binary operator that simplifies checking for null values. It returns the left-hand operand if the operand is not null, otherwise it returns the right-hand operand.
String Test1 = null; String retval1 = Test1 ?? "World"; Console.WriteLine(retval1);
This will give the ouput "World" Since the value of Test1 is null
String Test2 = "Murugan"; String retval2 = Test2 ?? "World"; Console.WriteLine(retval2);
This will give the ouput "Murugan" Since the value of Test2 is not null
??= is a null-coalescing assignment operator that assigns the value of its right-hand operand to its left-hand operand if and only if the left-hand operand evaluates to null. it doesn't evaluate its right-hand operand if the left-hand operand evaluates to non-null.