C Parser & Interpreter

A custom-built Compiler Frontend and Interpreter for a subset of the C language. This project implements the full pipeline from raw source code to execution, including Lexical Analysis, Parsing (AST), Semantic Validation, and Runtime Interpretation.

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✨ Features

1. Lexical Analysis (The Lexer)

• Converts raw source code into a stream of Tokens.
• Handles Keywords (int, print), Identifiers, Numbers, and Operators.
• Robust Error Handling: Detects invalid characters and malformed identifiers.

2. Syntax Analysis (The Parser)

• Implements a Recursive Descent Parser.
• builds a hierarchical Abstract Syntax Tree (AST).
• Handles Operator Precedence (multiplication * happens before addition +).
• Validates grammar rules (e.g., missing semicolons T_SEMICOLON).

3. Semantic Analysis (The Logic Check)

• Symbol Table: tracks variable declarations and memory state.
• Scope Validation:
  • Prevents using undeclared variables.
  • Prevents re-declaring existing variables.

4. Interpreter (The Runtime)

• Traverses the AST recursively to execute logic.
• Performs arithmetic calculations.
• Handles Runtime Errors (like Division by Zero).
• Executes print() statements to standard output.

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🛠️ Architecture

The project follows the standard compiler pipeline:

graph TD
    A[Source Code] -->|Lexer| B[Tokens]
    B -->|Parser| C[Abstract Syntax Tree (AST)]
    C -->|Semantic Check| D[Validated AST]
    D -->|Interpreter| E[Output / Result]

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💻 Tech Stack

• Language: C (Standard C99)
• Tools: GCC Compiler
• No External Libraries: Built completely from scratch (std libs only).

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🚀 How to Run

1. Clone the repository
2. Write your C code in inputfile.txt:

   int x = 10;
   int y = 5;
   int result = (x + y) * 2;
   print(result);

3. Compile the Parser:

   gcc parser.c -o parser

4. Run logic:

   ./parser inputfile.txt

   Note: You can pass any filename as an argument.

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📝 Supported Grammar

<program>         ::= <statement>*
<statement>       ::= <declaration> | <assignment> | <print_stmt>
<declaration>     ::= "int" IDENTIFIER "=" <expression> ";"
<assignment>      ::= IDENTIFIER "=" <expression> ";"
<print_stmt>      ::= "print" "(" <expression> ")" ";"
<expression>      ::= <term> { ("+" | "-") <term> }
<term>            ::= <factor> { ("*" | "/") <factor> }
<factor>          ::= NUMBER | IDENTIFIER | "(" <expression> ")"