function st2num,input,np,status
on_error,1
if input eq '' then input='0'          ;handle null case     
input=strtrim(input,2)
status=execute('output = ['+input+']') 
if not status then begin             ;handle erroneous input
 output=input & np=0
 message,'conversion failed',/continue
endif else begin
 s=size(output)
 if s(0) eq 0 then output=replicate(output,1)  ;convert scalar to vector
 np=n_elements(output)
endelse
return,output
end