st: generate a new categorical variable

[urbain thierry YOGO <yogout@gmail.com>]

Dear all
i have two variables Y and Z. Y is a dummy variable which takes 1 if
individual has access to water and 0 otherwise. Z is a categorical
variable which has the following structure:
Z=A if individual uses bleach to clean water
Z=B if individual use a filter to clean water
Z=C if individual use solar energy to clean water
Z=D if individual use absorbent cotton to clean water

Here is my problem. I want to generate a new variable X which should
be a combination of Y and Z. Here is the code i have written
gen X=0 if Y==0
replace X=1 if Y==1 & Z=="A"
replace X=2 if Y==1 & Z=="B"
replace X=3 if Y==1 & Z=="C"
replace X=4 if Y==1 & Z=="D"

My concern is that when i write this code, the first two lines work,
but after, there is 0 replacement. Please can somebody help me? Thank

-- 
*Urbain Thierry YOGO
Ph.D candidate in Economics*
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