What are common examiner traps in Context-Free Grammars and PDAs?

Overlooking base-case dimension constraints (e.g., failing to enforce dimension ≥ 1 vs allowing 0 dimensions) Misinterpreting split non-terminal boundaries, such as an opening bracket being produced by a parent non-terminal while the closing bracket is generated by a child non-terminal Assuming left-recursive and right-recursive variants cannot generate identical underlying languages

GATE CSE Context-Free Grammars and PDAs PYQs

Standard yield1.5% of Compiler Design

In Compiler Design, Context-Free Grammars (CFGs) are evaluated on their ability to correctly specify programming language constructs such as multi-dimensional a… Read the guide

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Questions: 1
Asked: 2016
Total marks: 2
Marks / paper: 0.1

1 GATE CSE Context-Free Grammars and PDAs PYQs with solutions, from Compiler Design. Browse all GATE CSE PYQs.

Questions

Every official paper that asked this topic, newest first.

GATE CSE 2016 Set 2 · Q46A student wrote two context-free grammars G1 and G2 for generating a single C-like array declaration. The dimension of the array is at least one. For example, int a[10][3]; The grammars use $D$ as the start symbol, and use six terminal symbols int ; id [ ] num. Grammar G1 $D \rightarrow \mathbf{int} \; L;$ …MCQ2 marksMediumSolve

What GATE tests in Context-Free Grammars and PDAs

Concepts, patterns, formulas and traps distilled from past papers.

In Compiler Design, Context-Free Grammars (CFGs) are evaluated on their ability to correctly specify programming language constructs such as multi-dimensional array declarations, variable definitions, and control structures. GATE tests the candidate's ability to trace derivations, verify language equivalence, and ensure that semantic and syntactic constraints (e.g., minimum dimension $\ge 1$ ) are strictly satisfied.

Core concepts

Context-Free Grammar (CFG) design for syntax specification
Left-recursive vs. right-recursive list-generation productions
Bracket balancing and token ordering in programming language grammar rules
Derivation sequences and language generation verification

Recurring question patterns

Grammar Validation for Programming Language Constructs
RareMCQ2 marks2016
Candidates are given a concrete language construct (such as a C-like multi-dimensional array declaration) and two candidate CFGs ( $G_1$ and $G_2$ ), and must determine which grammar(s) correctly derive strings of the required format.

Formulas GATE uses

General form for multi-dimensional array declaration

\text{Declaration} = \mathbf{int} \; \mathbf{id} \; ([\mathbf{num}])^+ ;

Determining whether candidate grammars derive all and only valid 1D and multi-dimensional array definitions.

Examiner traps in Context-Free Grammars and PDAs

Overlooking base-case dimension constraints (e.g., failing to enforce dimension ≥ 1 vs allowing 0 dimensions)
Misinterpreting split non-terminal boundaries, such as an opening bracket being produced by a parent non-terminal while the closing bracket is generated by a child non-terminal
Assuming left-recursive and right-recursive variants cannot generate identical underlying languages

How questions are asked

Grammar correctness evaluation for language construct (MCQ with 'Both', 'Only G1', 'Only G2', 'Neither')

Paper trends

Focus is placed on applying CFG concepts to practical programming language syntax specifications (e.g., recursive bracket matching in multi-dimensional declarations) rather than purely abstract language theory.
2016

Difficulty notes

Medium: Requires tracing base cases (1D array) and recursive cases (2D or higher dimension) across non-trivial production splits to verify that no spurious syntax is allowed and all valid strings are generable.