st: two STATA questions

["Ni Frank" <frankflying03@hotmail.com>]

Hi, I have two basic questions on STATA. 
1) There are 50 varialbes, w05100, w05200,....,w10000. We want to DROP 
those obversations for which at least one of the above variables takes 
value of 0.  When I use "drop if w*==0, it said "W* invalid name". 
Does anybody know what's wrong? 

2)  Now, if we want to KEEP those obersvations for which at least one 
of the variables w05100, w05200, ....,w09900 takes value of 0. How to 
do that? 

Thanks a lot!

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