GATE CS 2021 Set 2 Q.13 (CS Q.3): Parsing and Syntax Analysis (LL and LR)

Consider the following ANSI C program:

int main() {
    Integer x;
    return 0;
}

Which one of the following phases in a seven-phase C compiler will throw an error?

Lexical analyzer

Syntax analyzer

Semantic analyzer

Machine dependent optimizer

Official answer and solution

Solution

Trace compiler phases for the statement 'Integer x;' when Integer is not defined.

The program contains the statement Integer x; inside main().

Lexical Analysis: Integer matches the pattern of a valid identifier token, and x is another valid identifier. Both are recognized without error.

Syntax Analysis: The grammar of C includes productions of the form <type_name> <identifier>; (or typedef-name followed by variable name). The syntax analyzer builds a valid parse tree according to the context-free grammar rules.

Semantic Analysis: The compiler checks type declarations and symbol table entries. Because Integer has not been defined via typedef or as a primitive type, type resolution fails. The semantic analyzer reports an undeclared type error.

Final answer

The answer is the one in the official GATE answer key. The solution is this site's own explanation.

Paper: GATE 2021 Computer Science and Information Technology - Session 2 (CS2)
Question: 13 of 65, printed as CS Q.3
Section: Computer Science and Information Technology

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