可以用一个序列ARRAY在加VNAME函数完成。
以下是Sample Code：
data want;
set have;
array x(*) A B C D E;
do i=1 to dim(x);
if missing(x(i)) then x(i)=vname(x(i)) ;
end;
run;

The question is not clear itself.  It seems that you have data with 5 columns and there are missing values in some of columns. and you want to fill with values :  first column with A, second one with B, etc.

If that is case, it is pretty easy: you can use array if you have many columns to fix.  In you example,
you can simply use some ifthen statement:
   if  col_A is  ''  then col_A = "A" ;
   if  col_B is  ''  then col_B = "B" ;
   if  col_C is  ''  then col_C = "C" ;
   if  col_D is  ''  then col_D = "D" ;
   if  col_E is  ''  then col_E = "E" ;

变量类型是数值型，字母是字符型，怎么填充？