The error "C202: 'CS': undefined identifier" is a compiler error that occurs in certain programming languages, such as C or C++, when the compiler encounters a symbol or identifier (in this case, 'CS') that has not been defined or declared previously.

Here are some possible reasons for this error:

Typo: It's possible that there's a typo in the identifier name. Check to make sure that the spelling and capitalization of the identifier match its definition or declaration.

Missing declaration: The identifier may not have been declared or defined before it was used. Make sure to declare or define the identifier before using it in your code.

Scope issues: If the identifier was defined in a different scope (e.g., inside a function or block), it may not be visible outside of that scope. Make sure that the identifier is declared or defined in the correct scope.

Missing header file: If the identifier is part of a library or framework, you may need to include the appropriate header file to make it visible to the compiler. Check the documentation for the library or framework to see which header files are required.

To resolve the error, you'll need to identify the cause and take the appropriate action, such as correcting the typo, adding a declaration or definition, adjusting the scope, or including the necessary header file.