UNIVERSITY OF WEST ATTICA
SCHOOL OF ENGINEERING
DEPARTMENT OF COMPUTER ENGINEERING AND INFORMATICS

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Compilers

Design and Implementation of a Compiler at Uni-C

Vasileios Evangelos Athanasiou
Student ID: 19390005

GitHub · LinkedIn

Georgios Theocharis
Student ID: 19390283

GitHub

Ioannis Iliou
Student ID: 19390066

GitHub · LinkedIn

Pantelis Tatsis
Student ID: 20390226

GitHub · LinkedIn

Vasileios Dominaris
Student ID: 21390055

GitHub

Supervisor: Michalis Iordanakis, Special Technical Laboratory Staff

UNIWA Profile

Athens, May 2024

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Project Overview

This project involves the development of a compiler for Uni-C, a subset of the C programming language. The implementation was completed in three distinct phases, covering the fundamental stages of compiler construction:

1. Finite State Machine (FSM) Encoding
   Design and simulation of automata for recognizing lexical units.

2. Lexical Analysis (FLEX)
   Development of a lexical analyzer that identifies tokens using regular expressions.

3. Syntactic Analysis (BISON)
   Construction of a parser that validates program structure based on predefined grammar rules.

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Table of Contents

Section	Folder	Description
1	A-FLEX/	Lexical analysis phase using Finite State Machines and FLEX
1.1	A-FLEX/A2-FSM/	FSM design and implementation for Uni-C tokens
1.1.1	A-FLEX/A2-FSM/docs/	FSM theory notes, transition tables, and documentation (PDF/XLSX)
1.1.2	A-FLEX/A2-FSM/src/	FSM source files for identifiers, strings, numbers, comments, and whitespace
1.2	A-FLEX/A3-FLEX/	FLEX-based lexical analyzer implementation
1.2.1	A-FLEX/A3-FLEX/docs/	FLEX code documentation
1.2.2	A-FLEX/A3-FLEX/src/	FLEX source code, Makefile, input/output samples
1.3	A-FLEX/assign/	Assignment descriptions for Part A (FSM & FLEX)
2	B-BISON/	Syntax analysis phase using BISON
2.1	B-BISON/assign/	Assignment descriptions for Part B (BISON)
2.2	B-BISON/B2-FLEX-BISON/	Combined FLEX & BISON parser implementation
2.2.1	B-BISON/B2-FLEX-BISON/src/	Integrated lexer/parser source code and build files
2.3	B-BISON/B3-COMPILER/	Final compiler stage
2.3.1	B-BISON/B3-COMPILER/docs/	BISON grammar documentation
2.3.2	B-BISON/B3-COMPILER/src/	Final Uni-C compiler source code
3	Uni-C/	Language specification and usage guide for Uni-C

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Technical Specifications

1. Lexical Analysis (Tokens)

The compiler recognizes the following categories of tokens:

• Identifiers
  Names for variables and functions

  • Pattern: [a-zA-Z_][a-zA-Z0-9_]{0,31}

• Keywords
  Reserved words such as:

  • if, else, while, int, return, func

• Constants
  Supported constant types include:

  • Integers (decimal, octal, hexadecimal)
  • Floating-point numbers
  • Strings

• Operators

  • Arithmetic: +, -, *, /
  • Relational: >, <, ==
  • Logical: &&, ||

• Delimiters

  • Characters such as ; used to separate commands

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2. Finite State Machine (FSM)

For each token category, a Finite State Automaton (FSA) was designed.

Example – Identifiers:

• Starts at an initial state (SZ)
• Transitions to a middle-character state (SMCH) upon receiving a letter or underscore
• Reaches a GOOD exit state upon encountering a newline, provided the identifier is valid

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3. Syntactic Analysis (BISON)

The BISON parser generator is used to define and enforce grammar rules for Uni-C programs:

• Variable Declarations

  • Support for simple data types and arrays

• Functions

  • Recognition of both built-in and user-defined functions

• Expressions

  • Handling of simple and compound expressions

• Error Handling

  • Detection and reporting of syntax errors
  • Handling of invalid tokens (TOKEN ERROR)

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Project Files

• 1_identifiers.fsm
  FSM encoding for identifier recognition

• simple-flex-code.l
  FLEX source file containing regular expressions and token definitions

• token.h
  Header file defining numeric constants for tokens

• simple-bison-code.y
  BISON source file containing grammar and syntax rules

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Installation & Run Guide

Prerequisites

Before compiling, ensure the required tools are installed.

Required Packages

sudo apt update
sudo apt install gcc flex bison make

Verify Installation

gcc --version
flex --version
bison --version

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Install

Clone the repository

git clone https://github.com/Compilers-aka-Uniwa/Compiler-Uni-C.git

Navigate to project directory for testing the final version of Compiler

cd Compiler-Uni-C/B-BISON/B3-COMPILER/src

Also

Navigate to project directory for testing FSM

cd Compiler-Uni-C/A-FLEX/A2-FSM/src

Navigate to project directory for testing Flex

cd Compiler-Uni-C/A-FLEX/A3-FLEX/src

Navigate to project directory for testing Bison

cd Compiler-Uni-C/B-BISON/B2-FLEX-BISON/src

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A2 – Finite State Machines (FSM)

Directory

A2-FSM/src

Compile

cd A2-FSM/src
gcc fsm.c -o fsm

Run

./fsm

Notes

• FSM definitions are loaded from .fsm files (e.g. 1_identifiers.fsm, Final.fsm).
• Transition tables are documented in the accompanying PDF and Excel files.

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Open the Documentation

1. Navigate to the A-FLEX/A2-FSM/docs/ directory
2. Open the report corresponding to your preferred language:
   • English: Finite-State-Machines.pdf
   • Greek: Πεπερασμένα-Αυτόματα.pdf

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A3 – FLEX (Lexical Analyzer)

Directory

A3-FLEX/src

Compile (using Makefile)

cd A3-FLEX/src
make

Compile (manual)

flex simple-flex-code.l
gcc lex.yy.c -o flex_app

Run

./flex_app < input.txt

Output

output.txt

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Open the Documentation

1. Navigate to the A-FLEX/A3-FLEX/docs/ directory
2. Open the report corresponding to your preferred language:
   • English: Flex-Code.pdf
   • Greek: Κώδικας-Flex.pdf

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B3 – BISON (Syntax Analyzer)

Directory

B3-COMPILER/src

Compile (using Makefile)

cd B3-COMPILER/src
make

Compile (manual)

bison -d simple-bison-code.y
flex simple-flex-code.l
gcc simple-bison-code.tab.c lex.yy.c -o bison_app

Run

./bison_app < input.txt

Output

output.txt

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Open the Documentation

1. Navigate to the B-BISON/B3-COMPILE/docs/ directory
2. Open the report corresponding to your preferred language:
   • English: Bison-Code.pdf
   • Greek: Κώδικας-Bison.pdf

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B2 – FLEX + BISON (Complete Compiler Pipeline)

Directory

B2-FLEX-BISON/src

Compile (using Makefile)

cd B2-FLEX-BISON/src
make

Compile (manual)

bison -d simple-bison-code.y
flex simple-flex-code.l
gcc simple-bison-code.tab.c lex.yy.c -o compiler

Run (test input)

./compiler < input-test.txt

Run (final input)

./compiler < input-final.txt

Output

output.txt

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General Notes

• Each module provides its own Makefile for convenience.
• If execution permission is missing:

chmod +x <executable>

• The project has been tested on Linux (Ubuntu).
• For clean builds (when supported):

make clean

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Troubleshooting

• command not found: flex / bison Ensure the required packages are installed.

• Linker errors Re-run make clean and rebuild the project.

• Unexpected output Verify the correct input file is used and matches the grammar rules.