Issue while invoking the macro function

[deleted_user]

When I tried to invoke the macro function below, it throws an error saying
"%SYSEVALF function has no expression to evaluate...."

%macro concat_ctrl(contstr=,i=);
%do %while(&i < 32);
%let contstr = %sysfunc(cats(&contstr,%sysfunc(byte(&i))));
%put &contstr &i;
%let i=%eval(&i+1);
%end;
%mend concat_ctrl;
%concat_ctrl(contstr=%sysfunc(byte(0)), i=1);

But I am able to invoke the macro function above with difference values as below...

%macro concat_ctrl(contstr=,i=);
%do %while(&i < 72);
%let contstr = %sysfunc(cats(&contstr,%sysfunc(byte(&i))));
%put &contstr &i;
%let i=%eval(&i+1);
%end;
%mend concat_ctrl;
%concat_ctrl(contstr=%sysfunc(byte(65)), i=66);

Could you help me out to overcome this issue?

[martha_sas]

I do not have a complete explanation for you, but I believe your problem is that
byte(0) returns null, and sysfunc is getting a string with containing a null.

You can get the same error message submitting these two lines:

%let badstr=%sysfunc(cats(,1));
%put &badstr;