Four-Function Calculator

main.c

extern int yyparse(void);

int main() {
    yyparse();

    return 0;
}

mycalc.lex

%option noinput

%{
#include "mycalc.tab.h"
#include <stdlib.h>
%}

%option nounput

%%

[0-9]+ { yylval.value = strtod(yytext, 0); return T_FLOAT; }
"+" return T_PLUS_OPERATOR;
"-" return T_MINUS_OPERATOR;
"*" return T_MULTIPLICATION_OPERATOR;
"/" return T_DIVISION_OPERATOR;

[\n] { yylineno++; return T_STATEMENT_SEP; }
[ \t] ;

mycalc.y

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

%union {
	float value;
}

%token <value> T_FLOAT
%type <value> expression
%left T_MINUS_OPERATOR T_PLUS_OPERATOR
%left T_DIVISION_OPERATOR T_MULTIPLICATION_OPERATOR
%left T_STATEMENT_SEP

%start statements

%%

expression: T_FLOAT { $$ = $1; }
	| expression T_PLUS_OPERATOR           expression { $$ = $1 + $3; }
	| expression T_MINUS_OPERATOR          expression { $$ = $1 - $3; }
	| expression T_MULTIPLICATION_OPERATOR expression { $$ = $1 * $3; }
	| expression T_DIVISION_OPERATOR       expression { $$ = $1 / $3; }
	;

statement: expression T_STATEMENT_SEP { printf("%lf\n", $1); }
	| T_STATEMENT_SEP {}
	;

statements: statements statement
	| statement
	;

%%

int yyerror(const char *s)
{
	extern int yylineno;
	extern char *yytext;

	const char *text = yytext;
	if (strcmp(yytext, "\n") == 0) text = "\\n";

	fprintf(stderr, "Error: %s at '%s' on line %d\n", s, text, yylineno);

	exit(1);
}