Causes the compiler to report errors if variables are not declared before they are used.

/optionexplicit[+ | -]

+ | -

Optional. Specify /optionexplicit+ to require explicit declaration of variables. The /optionexplicit+ option is the default and is the same as /optionexplicit. The /optionexplicit- option enables implicit declaration of variables.

If the source code file contains an Option Explicit Statement (Visual Basic), the statement overrides the /optionexplicit command-line compiler setting.

To set /optionexplicit in the Visual Studio IDE

  1. Have a project selected in Solution Explorer. On the Project menu, click Properties. For more information, see Introduction to the Project Designer.

  2. Click the Compile tab.

  3. Modify the value in the Option Explicit box.

The following code compiles when /optionexplicit- is used.

Module Module1
    Sub Main()
        i = 99
    End Sub 
End Module