check whether a variable exists in a sas dataset

VARNUM checks whether the variable &name exists

data _null_; 

tableid=open('mydata','i');
if (sasname("&name")) then do;
   citynum=varnum(tableid,"&name");
   if (citynum=0) then
      call symput ('msg','The column is not in the table.');
   else
      call symput ('msg','The column number is '|| citynum );
end;
else
   call symput ('msg','Invalid SAS name--please reenter.');

run;