README

Installation of Bison and Flex

Linux (Ubuntu/Debian)

Run the following command to install Bison and Flex:

sudo apt update
sudo apt install bison flex -y

Linux (Fedora)

sudo dnf install bison flex -y

Linux (Arch Linux)

sudo pacman -S bison flex

macOS (Homebrew)

brew install bison flex

Windows (Using Cygwin or MSYS2)

For Cygwin:

1. Open Cygwin setup and search for "bison" and "flex" in the package selection.
2. Install them and complete the setup.

For MSYS2:

pacman -S mingw-w64-x86_64-bison mingw-w64-x86_64-flex

Verify Installation

After installation, check the installed versions:

bison --version
flex --version

If both commands return version numbers, the installation is successful.

Usage Example

To compile a Bison and Flex project:

bison -d parser.y
flex lexer.l
gcc lex.yy.c parser.tab.c -o my_parser
./my_parser

Example Bison and Flex Files

lexer.l (Flex File)

%{
    #include "parser.tab.h"
%}

%%

[0-9]+      { yylval.num = atoi(yytext); return NUMBER; }
[+\-*/()]   { return yytext[0]; }
[ \t\n]     { /* Ignore whitespace */ }
.           { printf("Unknown character: %s\n", yytext); }

%%

int yywrap() {
    return 1;
}

parser.y (Bison File)

%{
    #include <stdio.h>
    #include <stdlib.h>
    void yyerror(const char *s);
    int yylex();
%}

%union {
    int num;
}

%token <num> NUMBER
%token PLUS MINUS MULTIPLY DIVIDE LPAREN RPAREN
%left PLUS MINUS
%left MULTIPLY DIVIDE
%right UMINUS

%type <num> expr

%%

expr:
      expr PLUS expr      { $$ = $1 + $3; printf("Result: %d\n", $$); }
    | expr MINUS expr     { $$ = $1 - $3; printf("Result: %d\n", $$); }
    | expr MULTIPLY expr  { $$ = $1 * $3; printf("Result: %d\n", $$); }
    | expr DIVIDE expr    { 
        if ($3 == 0) { 
            printf("Error: Division by zero\n"); 
            $$ = 0;
        } else {
            $$ = $1 / $3; 
            printf("Result: %d\n", $$);
        }
      }
    | LPAREN expr RPAREN  { $$ = $2; }
    | MINUS expr %prec UMINUS { $$ = -$2; }
    | NUMBER              { $$ = $1; }
    ;

%%

void yyerror(const char *s) {
    fprintf(stderr, "Error: %s\n", s);
}

int main() {
    printf("Enter an expression:\n");
    return yyparse();
}

Running the Example

Once compiled, run the program:

./my_parser

Example input:

3 + 4 * 2

Expected output:

Result: 11