SAS - How to skip certain columns in a loop using arrays

I have a dataset that contains several numeric and character columns. Most of the character columns are simple 'yes' or 'no' questions but some are not. For the numeric columns I feel that I have a valid solution. For the character columns I have tried to minimize it but have not succeeded. What I want to do, and tried, is a loop that states that when j = column number of var4 then use the Big/Small/IU replacements. The idea is that this would make the code less “variable dependent” due to the fact that I can change the variable for var4 in the %let statement and the code would be shorter in length.

As the dim statement give me the total number of the numeric or character columns I guess that there are some statment that gives me the column placement of a specific variable that I would use for the secound loop. However, I have not found such a statement.

My code so far,

%let v1 = var1;
%let v2 = var2;
%let v3 = var3;
%let v4 = var4;

data have;
infile datalines delimiter = '|'; 
input surveyYear id var1 var2$ var3 var4$20. ;
datalines;
2016 |  1 |     10 |   Yes |     5 |   BIG
2016 |  2 |      6 |   YES |     8 |   Big
2016 |  3 |      8 |   YEs | 99999 |   big
2016 |  4 |      . |   yes |     5 | 99999
2017 |  5 |      6 |    No |     7 | SMALL
2017 |  6 |      5 |    Ye |     . | small
2017 |  7 |  99999 |    no |     3 | 99999
2018 |  8 |      3 | 99999 |     1 | SMall
2018 |  9 |      2 |    iu |     2 |    IU
2018 | 10 |     15 |    IU |     . |    Iu
;
run; 

data want;
set have;

    array var_num[*] _numeric_;
    do i=3 to dim(var_num);
        if var_num[i] = 99999 then var_num[i] = .;
    end;

    array var_cha[*] _character_;
    do j=1 to dim(var_cha);
        var_cha(j) = upcase(var_cha(j));
        if var_cha[j]  = 'YES'     then var_cha[j] = 'Yes';
        if var_cha[j]  = 'NO'      then var_cha[j] = 'No';
        if var_cha[j]  = 'IU'      then var_cha[j] = 'IU';
        if var_cha[j]  = '99999'   then var_cha[j] = 'IU';
        if var_cha[j]  = ''        then var_cha[j] = 'IU';
    end;
/* Integrate the code below into the loop*/
    if &v4 = 'BIG'     then &v4 = 'Big city';
    if &v4 = 'SMALL'   then &v4 = 'Small city';
    if &v4 = 'IU'      then &v4 = 'Unknow city size';
    if &v4 = '99999'   then &v4 = 'Unknow city size';

drop i j;
run;

The conceptual idea how i would like to program it,

data want;
set have;
array var_cha[*] _character_;
    do j=1 to dim(var_cha);
        var_cha(j) = upcase(var_cha(j));
/*      All of the if statements for the yes, no and IU */

        if var_cha[j] = ColumnNumerOfVar4 then do;
        /* where ColumnNumerOfVar4 is equal to the column number of var4*/
            if var_cha[j] =  'BIG'      then var_cha[j] = 'Big city';
            if var_cha[j] =  'SMALL'    then var_cha[j] = 'Small city';
            if var_cha[j] =  'IU'       then var_cha[j] = 'Unknow city size';
            if var_cha[j] =  '99999'    then var_cha[j] = 'Unknow city size';
        end;
    end;
run;