Hi! Please note the effect of Minus values.
data A;
input x @@;
if x then Expr="True ";
else Expr="False";
datalines;
1 -1 0 .
;

proc print noobs; run;

gives the result

x Expr
1 True
-1 True
0 False
. False

Perhaps the line -1 True is a surprise to some persons.