RDLC expression Switch use?

your code seems OK but what if both conditions not match? I have added default value for final condition.

=Switch(
    IsNumeric(Fields!C2.Value) and  Fields!C2.Value > 0, Fields!SeqNo.Value,
    1=1, Fields!C2.Value
    )

UPDATE:

for below:

if(C2 ==" ")
   {
    C2.Value = empty
   }
   else
   {
    C2.Value = Fields!SeqNo.Value
   }

try

=Switch(
    Fields!C2.Value = " ", "",
    1=1, Fields!C2.Value
    )