Recoding a NULL response value to a value of 0

[Bluekeys49]

I have 50 survey variables, named AB1, AB2, AB3,...,AB50.  Most of these variables contain a survey response, either answer choice A, B, or C.  In some cases, there is no response in which the field has NULL entered in the cell.  How do I change all of these NULL responses to a 0 without doing an if/then statement for each individual variable?  Thanks for any help!

[ketpt42]

data want;
    set have;
    array abvar{*} $ AB1-AB50;
    do i = 1 to dim(abvar);
        if missing(abvar(i)) then abvar(i) = '0';
    end; 
    drop i;
run;

[sustagens]

If variables are character, zero should be quoted

[Patrick]

If you need this only for display purposes then you can also use:

options missing='0';

Only works for numerical variables.

[Bluekeys49]

I neglected to mention that this survey is being imported in from Excel. The questions that were skipped (no response) were automatically populated with the word NULL when imported into SAS for analysis. So, wanting to change all occurrences of this text NULL value globally to 0 in any response field it exists.

[sustagens]

Change @ketpt42's code above to

if abvar(i)='NULL' then abvar(i) = '0';