I am using

=COLUMN(C:C)-COLUMN(A:A)+1

to calculate the number of the columns A to C (=3).
How can I use replace the C's and A's in the formula, referring to
cell-adresses?

The following formula does not result in 3.

=COLUMN(LEFT(C1,1):LEFT(C1,1))-COLUMN(LEFT(A1,1):LEFT(A1,1))+1

where contents cell C1 = C10 and cell A1 = A10 for example.

Who can help me on this?