Need help for macro to find and count matches in Excel

I need to create a macro to do the follow:
In a Excel table
A B C
------
a
b
c
d
i will paste a data in a column C for instance

A B C
------
a 0 b
b 0 b
c 0 f
d 0

The result I'm looking for is to find number of matches in A and B and if there is not match to add element to column A as follow:
A B C
-----
a 0 b
b 2 b
c 0 f
d 0
f 1