You missed the '+' operator :-)

try with USE mydatadir + '\' + aa1

and check that the aa1 datatype was a Charachter expression

>Dear Experts
>
>When I use followng command, it shows following error message
>Missing Operand
>What is wrong?
>Please modify
>
>

>close database
>MYDATADIR='D:\GIN2006\TABLES'
>
>aa1=thisform.text1.value	
>aa2=thisform.text2.value	
>aa3=thisform.text4.value
>
>USE &mydatadir\&aa1
>brow for(&aa2)=(&aa3)in window form1 noedit
>

>
>Data in variables
>
>aa1=vouchers.dbf
>aa2=vou_no (type n)
>aa3=1 (type n)