Basic (probably not working) calculator using flex/bison

calculator.l

%option noyywrap
%option outfile="scanner.c" header-file="scanner.h"

%{
        #include "calculator.tab.h"
        int yylval;
%}

%%

"+" { return ADD; }
"-" { return SUB; }
"*" { return MUL; }
"/" { return DIV; }
"|" { return ABS; }
[0-9]+ { yylval = atoi(yytext); return NUMBER; }
\n  { return EOL; }
[ \t] { /* ignore whitespace */ }
.   { printf("Unknown character: %s\n", yytext); }

%%

#if 0
int main(int argc, char **argv)
{
        int tok;

        while ((tok = yylex()))
        {
                printf("%d", tok);
                if (tok == NUMBER)
                        printf(" = %d", yylval);
                printf("\n");
        }

        return 0;
};
#endif

#if 0
int main(int argc, char **argv)
{
        if (argc > 1)
        {
                if (!(yyin = fopen(argv[1], "r")))
                {
                        perror(argv[1]);
                        return 1;
                }
        }


        yylex();

        return 0;
}
#endif

calculator.y

%{
#include <stdio.h>
#include "scanner.h"
extern int yyerror(const char *s);
%}

%token NUMBER
%token ADD SUB MUL DIV ABS
%token EOL
%%


calclist: /* Determine the expression grammar as <beginning of line> <expression> <end of line> */
        | calclist exp EOL { printf("= %d\n", $1); }
        ;

/* Determine the expressions ADD and SUB and calculate them */
exp: factor
   | exp ADD factor { $$ = $1 + $3; }
   | exp SUB factor { $$ = $1 - $3; }
   ;

/* Determine the expressions MUL and DIV and calculate them as well */
factor: term
      | factor MUL term { $$ = $1 * $3; }
      | factor DIV term { $$ = $1 / $3; }
      ;

/* Determine an absolute value and calculate it */
term: NUMBER
    | ABS term { $$ = $2 >= 0 ? $2 : - $2; }
    ;

%%

int main(int argc, char **argv)
{
        yyparse();
}

int yyerror(const char *s)
{
        fprintf(stderr, "Expression error: %s\n", s);
}

Makefile

CC=clang

CFLAGS=-Wall
LDFLAGS=-lfl


all:
        bison -d calculator.y
        flex calculator.l
        $(CC) $(CFLAGS) -c scanner.c -o scanner.o
        $(CC) $(CFLAGS) -c calculator.tab.c -o calculator.tab.o
        $(CC) *.o -o calc $(LDFLAGS)

clean:
        rm -f lex.yy.c calculator.tab.c calc calculator.tab.h scanner.c scanner.h *.o