tranwrd and substr text transformation question

[tianerhu]

libname cert 'C:\practice everyday\input';
libname results 'C:\practice everyday';
data results.output09;
set cert.input09;
a = substr(custID,3,4);
b = a*1000;
custID = tranwrd(custID,a,'9999');
run;
proc print data = results.output09;
run;

when I use variable a instead of 'substr(custID,3,4) as the second argument of the function tranwrd, it doesn't work. why?

The following is the data :

libname cert 'c:\cert\input';
Data cert.input09;
Input custID $;
Datalines;
ID1573
ID2369
ID5361
ID8902
;
Run;

[ChrisHemedinger · Accepted solution]

Try defining the A variable first with the proper type and length. You are replacing a character string, length of 4.

data results.output09;
length a $ 4;
set cert.input09;
a = substr(custID,3,4);
b = a*1000;
custID = tranwrd(custID,a,'9999');
run;

[tianerhu]

Thank you for your help.