Which statement best describes the semantic analysis phase of compilation?

• A. It tokenizes the source code
• B. It checks for semantic correctness such as type correctness and symbol resolution
• C. It constructs the syntax tree
• D. It generates machine code directly

Answer: (B)

Semantic analysis verifies what the program means after its structure has been recognized. It ensures the code makes sense within the language’s rules by checking type compatibility, ensuring variables and functions are properly declared and used, and resolving identifiers through the symbol table. In other words, it enforces that operations are applied to compatible types and that names refer to real, correctly typed entities, so the program is semantically valid before any code is produced.

For example, if a variable is declared as an integer and you try to use it in a context that requires a string, or you use a variable that hasn’t been declared at all, these are caught during semantic analysis. This stage relies on the information gathered earlier (like declarations and types) and prepares a correctly annotated representation of the program for the next phase.

Tokenizing belongs to lexical analysis, which breaks source code into tokens. Constructing the syntax tree is the job of parsing. Generating machine code directly is done in the code generation phase.