I need update a cell if a given condition is true, but I need that cell keeps its old value if the given condition is not true.
For example, try these in cell A1:

=if(C4=1,A2,A1)
=if(C4=1,A2 , )
if(C4=1,A2)

It seems ok, but now type this in cell B1 : =A1 and press enter.
Surprise!

It must be possible to leave a celle unchanged!

Please help!

Thanks