Identifier and Keyword Recognition

Your Task

Implement efficient identifier scanning with keyword recognition.

Requirements

1. Implement scan_identifier() that:

   • Starts when seeing a letter or underscore
   • Continues while seeing letters, digits, or underscores
   • Returns the complete identifier/keyword

2. Implement lookup_keyword() that:

   • Takes an identifier string
   • Returns the appropriate keyword TokenType if matched
   • Returns TOKEN_IDENTIFIER otherwise

3. Support these C keywords (minimum):

   • Types: int, char, void, float, double
   • Control flow: if, else, while, for, return
   • Other: struct, const, sizeof

4. Handle edge cases:

   • int123 is identifier, not keyword + number
   • _private is valid identifier
   • Keywords are case-sensitive (INT is identifier, not keyword)

Success Criteria

• int recognized as TOKEN_INT
• integer recognized as TOKEN_IDENTIFIER
• _int recognized as TOKEN_IDENTIFIER