It is not necessary to declare a variable before using it but we should declare all the variables before assigning the values so that we can reduce the time of debugging our script. We can declare a variable by using dim keyword.

Dim is the short form of "Dimension". It is the VBScript syntex and there will be no problem to execute a page where we used variables without declaring unless we put the "Option Explicit" statement to check the variables are properly declared.

(1) Using variables in an ASP Page

(2) Using "Option Explicit" Statement