Underline unknown symbols as you write code. Symbols that are mistyped, not defined, or used out of context are underlined.
Visual Assist versus Visual Studio
Microsoft introduced squiggles for unknown symbols in Visual Studio 2010. Visual Assist will not underline symbols, irrespective of the setting in its options dialog, if you leave the IDE setting enabled.
Select the color of underlining in the Visual Assist options dialog.
Visual Assist does not underline symbols that exist when you open a file, even though the symbols may be undefined or used out of context, because Visual Assist assumes initially that you opened the file only to read it. Underlining of unknown symbols begins after you modify a file.
Symbols in Macros
Unknown symbols passed to C/C++ preprocessor macros are not underlined. Visual Assist assumes the macro defines the symbol.