C Syntax Validator using PLY

This mini-project was developed as part of a course on Automata, Formal Languages, and Logic.

It uses PLY (Python Lex-Yacc) to perform syntax validation of a simple subset of the C programming language. It supports:

• Constant and variable declarations
• Arithmetic expressions
• Basic syntax error detection

📌 Objective

This project demonstrates how context-free grammars can be applied to perform syntax validation on simplified C-like statements using Python's PLY (Lex and Yacc) library. It helps understand the fundamentals of parsing and compiler construction.

✨ Features

• Tokenizes input using a custom lexer
• Parses statements using defined CFG rules
• Supports:
  • int and const int declarations
  • Arithmetic operations: +, -, *, /
  • Grouped expressions using {} and ()
  • Syntax error detection and handling

🔧 Files

• main1.py - Main interactive prompt
• lexer1.py - Tokenizer using PLY
• parser1.py - Grammar rules and CFG parser using PLY

▶️ How to Run

Make sure you have PLY installed:

pip install ply

Then run the program:

python main1.py

You will get a prompt like this:

>

Now you can input C statements. Example:

const int x = 5;
x + 3 * 2;

It will output:

Declared constant x = 5
Expression evaluated: 11

⚠️ Note:

The input is read line-by-line. If you want to enter code blocks using { ... }, you must enter the entire block on a single line. For example:

{ int x = 3; int b = 10; x + b; }

📚 Example Inputs

int a = 5;
a + 4;

const int b = 10;
{ int x = 3; x + b; }

💻 Sample Output

> int a = 5;
Declared a = 5

> const int b = 10;
Declared constant b = 10

> a + b;
Expression evaluated: 15

> y = 2;
y = 2

> b + ;
Syntax error at ';'

👩‍💻 Author

Shree Raksha (she/her)
B.Tech in Computer Science, PES University
GitHub: @shreeraksha-cs

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