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GATE CSE Compiler Design — practice questions

Explore 23 free Compiler Design questions in GATE CSE Computer Science. Open each question or exercise to read its content, reference answers and available explanation.

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Compiler Design questions and exercises with answers

Showing questions 1–23 of 23.

The SCANNER (or LEXER) is the FIRST phase of a compiler. Its job is toRead the answer and worked solution →The DIFFERENCE between a TOKEN and a LEXEME isRead the answer and worked solution →Which formalism is most commonly used to specify the LEXICAL structure of programming language tokens?Read the answer and worked solution →The MAXIMAL MUNCH rule for lexical analysis says that when two rules can both matchRead the answer and worked solution →How are RESERVED WORDS (keywords like 'if', 'while') typically handled by a scanner?Read the answer and worked solution →A scanner usually IGNORES which characters?Read the answer and worked solution →An IDENTIFIER in most C-family languages follows the regexRead the answer and worked solution →A FINITE AUTOMATON used in the scanner is typicallyRead the answer and worked solution →If a programmer writes `1.5e3` in a C-style language, the scanner should produceRead the answer and worked solution →In an LL(1) language, the scanner produces tokens that the parser examinesRead the answer and worked solution →Which is a token (TYPE) emitted by a typical C-style scanner?Read the answer and worked solution →A PARSER converts a stream of tokens intoRead the answer and worked solution →RECURSIVE DESCENT parsers translate each grammar rule intoRead the answer and worked solution →Recursive descent is a TOP-DOWN parsing strategy. Its main weakness isRead the answer and worked solution →An AMBIGUOUS grammar is one whereRead the answer and worked solution →How does a parser typically encode OPERATOR PRECEDENCE in the grammar?Read the answer and worked solution →What is a SYNTAX ERROR?Read the answer and worked solution →PANIC MODE error recovery in a parser works byRead the answer and worked solution →LL parsers (recursive descent) parse from theRead the answer and worked solution →A SHIFT/REDUCE CONFLICT in an LR parser occurs whenRead the answer and worked solution →After the parser produces an AST, the next compiler phase is typicallyRead the answer and worked solution →The FIRST(α) set of a string α in LL parsing isRead the answer and worked solution →The FOLLOW(A) set in LL parsing isRead the answer and worked solution →

Worked practice questions

The SCANNER (or LEXER) is the FIRST phase of a compiler. Its job is to

  1. execute the source code
  2. optimise the program
  3. produce machine code directly
  4. produce a token stream
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Correct answer: D. produce a token stream

1. The scanner reads the source code as a sequence of CHARACTERS. 2. It groups those characters into meaningful chunks called TOKENS — the 'words' and 'punctuation' of the programming language. 3. Output: a stream of tokens (each with a type, lexeme, literal, line number). 4. Subsequent phases (parser, semantic analyser, code generator) work on this token stream instead of raw text. 5. Options A, C, D describe later phases (interpreter, code gen, optimiser). _Source: Bob Nystrom, "Crafting Interpreters", Ch 4 (Scanning, intro)._

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The DIFFERENCE between a TOKEN and a LEXEME is

  1. they are synonyms
  2. lexeme = substring; token adds type
  3. a token is shorter than a lexeme
  4. lexemes are reserved words only
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Correct answer: B. lexeme = substring; token adds type

1. LEXEME: the specific raw substring of source code that forms a token, e.g. 'while', '123', 'x', '+='. 2. TOKEN: a richer structure containing the lexeme PLUS: - TYPE (e.g. KEYWORD_WHILE, NUMBER, IDENTIFIER, PLUS_EQUAL) - LITERAL value (for numbers, strings — parsed into typed value) - SOURCE LOCATION (line and column) 3. Example: '123' is the lexeme; the token is `(NUMBER, 123, line=4)`. 4. Options A, C, D mischaracterise. _Source: Bob Nystrom, "Crafting Interpreters", Ch 4.2 (Lexemes and Tokens)._

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Which formalism is most commonly used to specify the LEXICAL structure of programming language tokens?

  1. Turing machines
  2. Context-free grammars
  3. Regular expressions
  4. Predicate logic
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Correct answer: C. Regular expressions

1. Lexical structure is REGULAR: tokens like identifiers, numbers, keywords can be described by REGULAR EXPRESSIONS. 2. Regex → NFA → DFA. The DFA becomes the scanner table. 3. Tools like lex, flex, ANTLR use this exact pipeline. 4. Context-free grammars (option B) are used for SYNTAX (parser), not lexical analysis. Turing machines and predicate logic are far more powerful than needed for tokenisation. _Source: Bob Nystrom, "Crafting Interpreters", Ch 4.3 (Regular Languages and Expressions)._

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