C .

the SUM statement is a compile-time instruction exactly equivalent to using the SUM function and the RETAIN statement:
   retain variable 0;
  variable=sum(variable,expression);

so.....
data WORK.NEW /debug;
    set WORK.OLD;
  retain count 0;
    count=sum(Count,1);
run;

请问这是今天的考题吗？我15号考试，能加我吗？MSN:benwan2009@hotmail.cm。QQ:913348978

c,昨天我考的时候有这一题

It seems not  work in SAS with  "/debug".

Here is a way to see.

206  data t1;
207    x=1;
208    output; output; output;
209    run;

NOTE: The data set WORK.T1 has 3 observations and 1 variables.
NOTE: DATA statement used (Total process time):
      real time           0.01 seconds
      cpu time            0.01 seconds


210
211  data _null_;
212    put '0>>> ' _all_;
213    stop;
214    do until(end);
215    put '1>>> ' _all_;
216    set t1 end=end nobs=nobs;
217     put '2>>>' _all_;
218    c+1;
219     put '3>>>' _all_;
220     end;
221   run ;

0>>> end=0 nobs=3 x=. c=0 _ERROR_=0 _N_=1
NOTE: There were 1 observations read from the data set WORK.T1.
NOTE: DATA statement used (Total process time):
      real time           0.00 seconds
      cpu time            0.00 seconds