Syntax analysis or parsing is the second phase of a compiler. 

First we should know why CFG needed ?

The main task of the lexical analyzer is to read the input characters of the source program group them into lexemes and produce as output a sequence of tokens..

A lexical analyzer can identify tokens with the help of regular expressions and pattern rules. 

But a lexical analyzer cannot check the syntax of a given sentence due to the limitations of the regular expressions. 

Regular expressions cannot check balancing tokens, such as parenthesis. 

Therefore, this phase uses context-free grammar (CFG), which is recognized by push-down automata.

CFG is a superset of Regular Grammar.

It implies that every Regular Grammar is also context-free, but there exists some problems, which are beyond the scope of Regular Grammar.

CFG is a helpful tool in describing the syntax of programming languages. 

What is Context-Free Grammar ?

A context-free grammar (CFG) consisting of a finite set of grammar.

A context-free grammar has four components:
  1. Non-terminals (V): Non-terminals are syntactic variables that denote sets of strings.
  2. Terminal symbols (Σ): Terminals are the basic symbols from which strings are formed. 
  3. Productions (P): The productions of a grammar specify the manner in which the terminals and non-terminals can be combined to form strings. Each production consists of a non-terminal called the left side of the production, an arrow, and a sequence of terminals, called the right side of the production. 
  4. Start symbol (S): From where the production begins.

For example, in CFG, S --> 0 | 1A, A --> 1

V = {S, A}
Σ = {0, 1}
P = {S-->0| S --> 1A | A --> 1}
S = {S}

What is Syntax Analyzers ?

A syntax analyzer or parser takes the input from a lexical analyzer in the form of token streams. 

The parser analyzes the source code (token stream) against the production rules to detect any errors in the code. 

The output of this phase is a parse tree.

More topics to read in Compiler Design

Python Programming ↓ 👆
Java Programming ↓ 👆
JAVA covered following topics in these notes.
JAVA Programs
Principles of Programming Languages ↓ 👆
Principles of Programming Languages 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 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 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.