yacc arithmetic

 

YACC arithmetic expression

First, make sure you have Flex installed:
For installing on Ubuntu- sudo apt-get install flex bison

How to Compile and Run:

Clean and rebuild:
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bison -d parser.y flex lexer.l gcc lex.yy.c parser.tab.c -o calculator -lm
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Run the calculator:
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./calculator
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Just in case -
rm -f lex.yy.c parser.tab.* calculator
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---Save as lexer.l--- %{ #include "parser.tab.h" #include <stdlib.h> extern char* yytext; void yyerror(char *); %} %% [0-9]+(\.[0-9]+)? { yylval.dval = atof(yytext); return NUMBER; } [ \t] ; /* ignore whitespace */ \n { return '\n'; } . { return yytext[0]; } %% int yywrap(void) { return 1; }
​
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---Save as parser.y--- %{ #include <stdio.h> #include <math.h> void yyerror(char *); int yylex(void); extern char* yytext; %} %union { double dval; } %token <dval> NUMBER %type <dval> expr %left '+' '-' %left '*' '/' %right UMINUS %% input: /* empty */ | input expr '\n' { printf("= %g\n", $2); } | input '\n' /* ignore empty lines */ ; expr: NUMBER { $$ = $1; } | '(' expr ')' { $$ = $2; } | expr '+' expr { $$ = $1 + $3; } | expr '-' expr { $$ = $1 - $3; } | expr '*' expr { $$ = $1 * $3; } | expr '/' expr { $$ = $1 / $3; } | '-' expr %prec UMINUS { $$ = -$2; } ; %% void yyerror(char *s) { fprintf(stderr, "Error: %s\n", s); } int main(void) { printf("Enter arithmetic expressions (one per line, Ctrl+D to exit):\n"); yyparse(); return 0; }

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