Expression Evaluator

Overview

This is a simple parser and evaluator for mathematical expressions built using Flex (scanning) and Bison/Yacc (parsing).

It supports basic arithmetic operations, conditional statements, and variable assignments.

This is a group project for a Compiler Construction class

Contributors:

1. Jesse Kamau
2. Singh Sehmi
3. Aman Vasani
4. Sylvester Leting
5. Adrian Oduma

Features

• Supports arithmetic operations: addition, subtraction, multiplication, and division.
• Handles conditional statements (if and else).
• Allows variable assignments and lookups.
• Generates an Abstract Syntax Tree (AST) for parsed expressions.

Project Structure

• ast.c & ast.h: Function definitions for creating & manipulating the Abstract Syntax Tree (AST).
• symbol.c & symbol.h: Implements a symbol table for managing variable names and their types.
• parser.y: Bison grammar file that defines the syntax and rules for parsing expressions.
• parser.tab.c & parser.tab.h: Generated files from Bison that contain the parser implementation (run bison -v -d parser.y to generate them).
• lex.yy.c: Generated file from Flex that contains the lexical analyzer (run flex lexer.l to generate it).
• Makefile: Build script to compile/automate the whole project.

Pre-requisites

• Ubuntu (or preferred Linux distro)
• GCC
• Flex
• Bison
• Make

Installation

Modify parser.y and lexer.l with the correct grammar & tokens declaration then run:

bison -v -d parser.y
flex lexer.l
gcc -o -Wall parser ast.c symbol.c parser.tab.c lex.yy.c -lfl

Build the project:

make

Source files are compiled and an executable file is created -> expression_evaluator.

Error Handling

The parser wiil report syntax errors if the input does not align with defined grammar in parser.y or tokens declaration in lexer.l.

To debug errors, run:

bison -v -d -Wcounterexamples parser.y

Usage

Run the compiled program:

./expression_evaluator

Enter expressions and end them with a semicolon (;). Type exit or CTRL+C to terminate the program.

Examples of Expressions you can input:

a = 5 + 3;

if (a > 3) b = 10 else b = 20;

x = 5;
y = 10;
z = x + y;

Contributing

Contributions are welcome! Please feel free to submit a pull request or open an issue for any enhancements or bug fixes.

License

This project is licensed under the MIT License - see the LICENSE file for details.