Hello Keval, Here is an excerpt from the Introduction to IDL training guide that should be helpful: Variables do not have to be declared in IDL. The type of a variable is determined by its usage. If a variable is set equal to the sum of two floating point numbers, the variable will be a float. IDL variables can easily be converted between types. Initially, all variables are undefined. It is illegal to use an undefined variable in an expression. There are three valid organizational structures for IDL variables: - Scalar - Array (from one to eight dimensions) - Structure (an aggregate of other variables of various data types and organizations) Cheers, Molly - on behalf of RSI Technical Support Research Systems, Inc.