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Option Explicit Statement
If used, the Option Explicit statement must appear in a module before any procedures.
When Option Explicit appears in a module, you must explicitly declare all variables using the Dim, Private, Public, ReDim, or Static statements. If you attempt to use an undeclared variable name, an error occurs at compile time.
If you don't use the Option Explicit statement, all undeclared variables are of Variant type unless the default type is otherwise specified with a Deftype statement.
Use Option Explicit to avoid incorrectly typing the name of an existing variable or to avoid confusion in code where the scope of the variable is not clear.
This example uses the Option Explicit statement to force explicit declaration of all variables. Attempting to use an undeclared variable causes an error at compile time. The Option Explicit statement is used at the module level only.
Option explicit ' Force explicit variable declaration. Dim MyVar ' Declare variable. MyInt = 10 ' Undeclared variable generates error. MyVar = 10 ' Declared variable does not generate error.