Checking datatype of CHAR variable in 4GL

Does anyone if there a function in Informix 4gl (version 4) which will let you check the contents of a CHAR variable to see whether or not it is a valid number, without causing a numeric conversion error? I have an application which is requesting input from the user, and the input can be a number, or a string. This then gets put through a CASE statement, more or less as follows: DEFINE var CHAR(5) PROMPT "Enter data: " FOR var CASE WHEN var>=1 AND var<=9999 DISPLAY "Var is a number" WHEN var IS NOT NULL DISPLAY "Var is a string" END CASE The problem I've got is that if the user enters a string, the program bombs out with a "Character to numeric conversion error" at the first WHEN clause. Lastly, does anyone know if there is a "catchall" WHEN statement (like the * in a UNIX shell CASE statement). Thanks for any suggestions! Regards, Ben