• Lexical analyzer generator scans the input stream and converts sequences of characters into tokens.
  • The main job of lexical analyzer (scanner) is used to break up an input stream into more usable element(tokens)
  • Lex is not a complete language, but rather a generator representing a new language feature which can be added to different programming languages, called host languages.

What is Token in Lex ?

Token is a classification of groups of characters.
For example:











  • Lex is a tool for writing lexical analyzers.
  • Lex reads a specification file containing regular expressions and generates a C routine that performs lexical analysis. Matches sequences that identify tokens.

A Lex program consist of 3 sections:
  • The first section of declaration includes declaration of variable, constants and regular definition.
  • The second section is for translation rules which consists of regular expression and action with respect to it. 
  • The third section holds whatever program subroutine are needed by the action.
Ambiguous Source Rules:
  • Lex can handle ambiguous specifications. When more than one expression can match the current input, Lex chooses as follows:
  1. The longest match is preferred.
  2. Among rules which matched the same number of characters, the rule given first is preferred.

More topics to read in Compiler Design

Compiler Design

EasyExamNotes.com covered following topics in Compiler Design.
  1. LEX
  2. Data structure in CD
  3. Specification & Recognition of Tokens
  4. Bootstrapping n porting
  5. Phases of compiler
  6. Input buffering
  7. Syntax analysis CFGs
  8. L-attribute definition
  9. LR parser
  10. Operator precedence parsing
  11. Analysis of syntax directed definition
  12. Recursive descent parser
  13. Recursive analysis/span
  14. Function and operator overloading
  15. Storage allocation strategies
  16. Equivalence of expression in type checking
  17. Storage organization
  18. Parameter passing
  19. Run time environment
  20. Type checking
  21. Polymorphic function
  22. Case statement CD
  23. Code generation issue in design of code generator
  24. Boolean expression
  25. Register allocation & assignment
  26. Intermediate code generation declaration and assignments
  27. Analysis synthesis model of compilation
  28. Code optimization
  29. Sources of optimization of basic blocks
  30. Loops in flow graphs
  31. Dead code elimination
  32. Loop optimization
  33. Introduction to global data flow analysis
  34. Data flow analysis of structure flow graph
Python Programming ↓ 👆
Java Programming ↓ 👆
JAVA EasyExamNotes.com covered following topics in these notes.
JAVA Programs
Principles of Programming Languages ↓ 👆
Principles of Programming Languages
EasyExamNotes.com covered following topics in these notes.

Previous years solved papers:
A list of Video lectures References:
  1. Sebesta,”Concept of programming Language”, Pearson Edu 
  2. Louden, “Programming Languages: Principles & Practices” , Cengage Learning 
  3. Tucker, “Programming Languages: Principles and paradigms “, Tata McGraw –Hill. 
  4. E Horowitz, "Programming Languages", 2nd Edition, Addison Wesley

    Computer Organization and Architecture ↓ 👆

    Computer Organization and Architecture 

    EasyExamNotes.com covered following topics in these notes.

    1. Structure of desktop computers
    2. Logic gates
    3. Register organization
    4. Bus structure
    5. Addressing modes
    6. Register transfer language
    7. Direct mapping numericals
    8. Register in Assembly Language Programming
    9. Arrays in Assembly Language Programming


    1. William stalling ,“Computer Architecture and Organization” PHI
    2. Morris Mano , “Computer System Organization ”PHI

    Computer Network ↓ 👆
    Computer Network

    EasyExamNotes.com covered following topics in these notes.
    1. Data Link Layer
    2. Framing
    3. Byte count framing method
    4. Flag bytes with byte stuffing framing method
    5. Flag bits with bit stuffing framing method
    6. Physical layer coding violations framing method
    7. Error control in data link layer
    8. Stop and Wait scheme
    9. Sliding Window Protocol
    10. One bit sliding window protocol
    11. A protocol Using Go-Back-N
    12. Selective repeat protocol
    13. Application layer
    1. Andrew S. Tanenbaum, David J. Wetherall, “Computer Networks” Pearson Education.
    2. Douglas E Comer, “Internetworking with TCP/IP Principles, Protocols, And Architecture",Pearson Education
    3. KavehPahlavan, Prashant Krishnamurthy, “Networking Fundamentals”, Wiley Publication.
    4. Ying-Dar Lin, Ren-Hung Hwang, Fred Baker, “Computer Networks: An Open Source Approach”, McGraw Hill.