I have data in 3 columns.using "if "' condition I have to, upto a
certain number, fill a value in 4th column.There may be blank cells in
4th column.Again I have to scroll down the rows and fill blank cells
in the 4th column using another "if " condition.That is I want to
fill cells in 4th column, only when it is blankHow to do it?
I have given an illustration below;

Excel Sheet contains data as follows:
A B C D
1 S M 1
2 B F 1
3 M F 2
4 S M 1
5 B M 1
6 S M 1
7 M F 2
8 S M 1
Using if condition that is if A=''S" and B="M", I fill 4th column 1st
and 4th row with a value "True1" for 2 times

A B C D
1 S M 1 True1
2 B F 1
3 M F 2
4 S M 1 True1
5 B M 1
6 S M 1
7 M F 2
8 S M 1


Again i want to use another set of If conditions such as if A=S,and
B=M ,I want to fill 4th column 6th and 8 th rows with a value "True2"
for 2 times as shown below:


A B C D
1 S M 1 True1
2 B F 1
3 M F 2
4 S M 1 True1
5 B M 1
6 S M 1 True2
7 M F 2
8 S M 1 True2