Preprocessor chicanery

Understanding C++ preprocessor behavior in interview code puzzles

This is a medium-difficulty C++ language-knowledge question that tests your grasp of how the preprocessor works in practice. Quant firms and trading platforms use questions like this to confirm you understand macro expansion, token pasting, and the order in which the preprocessor and compiler operate—knowledge that becomes critical when debugging production code or reading legacy systems.

To solve preprocessor puzzles, you need to mentally trace macro substitution, understand how #define directives interact with scope, and recognize common pitfalls around parenthesization and side effects. The question rewards precise understanding of preprocessor semantics, not just intuition about what code "should" do.

• Macro expansion and text substitution rules
• Token pasting and stringification operators
• Scope and lifetime of preprocessor definitions
• How macros interact with the C++ compiler proper