Hi! A mistake I made recently. Question: How to find it easily ?
This is not a SAS error - it is a programming mistake, which is perhaps not easy to see if you are tired. The effect in this case is "radical".

data A;
input x @@;
if x then; Expr="True "; /* The left-most semicolon added by mistake. */
datalines;
1 0 .
;

proc print noobs; run;

result:
x Expr
1 True
0 True
. True

/ Br Anders