Compiler Brain Teasers: Lexical Edition

What is the main role of a lexical analyzer in a compiler?

• Optimize intermediate code

• Parse the syntax of the program

• Translate code to machine language

• Convert source code into tokens

Which of the following is used by Lex to describe patterns for tokens?

• Assembly instructions

• Regular expressions

• Context-free grammar

• DFA transition tables

In Lex, which variable stores the matched lexeme?

• yytok

• yylval

• yytext

• yyparse

What function is called to start the scanning process in a Lex program?

• main()

• yylex()

• yytext()

• scanf()

Which of the following regular expressions matches a valid identifier in C?

• [0-9][a-zA-Z_]*

• [a-zA-Z_][a-zA-Z0-9_]*

• [A-Z_][0-9a-z]*

• [a-z][A-Z]*

What is the use of the %% symbol in a Lex file?

• Starts the C code section

• Denotes the end of file

• Separates sections (definitions, rules, C code)

• Comments out code

What is the output of Lex after processing input?

• Syntax tree

• Assembly code

• Intermediate code

• Token stream

Which token(s) will be recognized by this rule?

• 123abc

• value1

• -count

• @temp

What will be the output if the input is 123abc?

• NUMBER: 123abc

• NUMBER: 123

  IDENTIFIER: abc

• IDENTIFIER: 123abc

• UNKNOWN: 123abc

What is a token in the context of a compiler?

• A compiled program

• A type of syntax tree

• A line of code

• A meaningful sequence of characters (like keywords, identifiers)