Implementing a lexical analyzer in Compiler Design - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding the role of a lexical analyzer

What is the primary function of a lexical analyzer in a compiler?

A It generates machine code from intermediate representation.

B It optimizes the syntax tree for faster execution.

C It converts source code into a sequence of tokens by grouping characters.

D It manages memory allocation during program execution.

💡 Hint

Think about the first step after reading raw source code characters.

The lexical analyzer reads raw characters and groups them into meaningful units called tokens, which are then passed to the parser.

📋 Factual

intermediate

Token recognition in lexical analysis

Which of the following best describes how a lexical analyzer recognizes tokens?

A By using regular expressions to match patterns in the input stream.

B By constructing abstract syntax trees directly from characters.

C By executing semantic actions during parsing.

D By generating machine instructions for each character.

💡 Hint

Consider how patterns like identifiers or numbers are detected.

Lexical analyzers use regular expressions or finite automata to match patterns and identify tokens in the input stream.

🔍 Analysis

advanced

Handling ambiguous token patterns

Given the token patterns for identifiers (letters followed by letters or digits) and keywords (specific reserved words), how should a lexical analyzer handle the input ifelse?

A Recognize <code>ifelse</code> as a single identifier token.

B Split into two tokens: keyword <code>if</code> and identifier <code>else</code>.

C Split into two tokens: keyword <code>if</code> and keyword <code>else</code>.

D Raise an error because <code>ifelse</code> is not a valid token.

💡 Hint

Think about longest match rule and reserved words.

The lexical analyzer applies the longest match rule, so it recognizes ifelse as one identifier token since it does not match the keyword if or else separately.

❓ Comparison

advanced

Differences between lexical analyzer and parser

Which statement correctly distinguishes the lexical analyzer from the parser in a compiler?

A The lexical analyzer executes semantic actions; the parser performs lexical analysis.

B The lexical analyzer generates machine code; the parser optimizes it.

C The lexical analyzer manages memory; the parser handles input/output operations.

D The lexical analyzer groups characters into tokens; the parser analyzes token sequences to build syntax trees.

💡 Hint

Consider the roles of tokenization and syntax analysis.

The lexical analyzer converts raw characters into tokens, while the parser takes these tokens and builds a structured representation like a syntax tree.

❓ Reasoning

expert

Error detection in lexical analysis

Consider a lexical analyzer that encounters the input string @variable, where @ is not part of any token pattern. What is the best way for the lexical analyzer to handle this situation?

A Replace <code>@</code> with a space and continue scanning.

B Report a lexical error immediately and stop processing further input.

C Treat <code>@</code> as a valid token and include it in the token stream.

D Ignore the <code>@</code> character and continue scanning the rest as tokens.

💡 Hint

Think about the importance of detecting invalid characters early.

Lexical analyzers must detect invalid characters and report errors to prevent incorrect parsing later. Ignoring or altering input can cause confusion and incorrect compilation.