Multiple Variable Calculator Flex/Bison -
i'm writing calculator in flex/bison allows variables. right have 1 variable (x) can use. want able use more x. (rather a-z). can help? here's have far:
calculator.y
%{ #include <stdio.h> #include <math.h> void yyerror(char *); int yylex(void); int symbol; %} %token integer variable %left '+' '-' '*' '/' '^' %% program: program statement '\n' | /* null */ ; statement: expression { printf("%d\n", $1); } | variable '=' expression { symbol = $3; } ; expression: integer | variable { $$ = symbol; } | '-' expression { $$ = -$2; } | expression '+' expression { $$ = $1 + $3; } | expression '-' expression { $$ = $1 - $3; } | expression '*' expression { $$ = $1 * $3; } | expression '/' expression { $$ = $1 / $3; } | expression '^' expression { $$ = pow($1, $3); } | '(' expression ')' { $$ = $2; } ; %% void yyerror(char *s) { fprintf(stderr, "%s\n", s); } int main(void) { yyparse(); } calculator.l
/* calculator */ %{ #include "y.tab.h" #include <math.h> #include <stdlib.h> void yyerror(char *); %} %% [x] { yylval = *yytext - 'a'; return variable; } [0-9]+ { yylval = atoi(yytext); return integer; } [-+*/^()=\n] { return *yytext; } [ \t] ; /* skip whitespace */ . yyerror("unknown character"); %% int yywrap(void) { return 1; }
your lexer needs recognize [a-z] instead of [x].
in grammar, need define array int variables[26];
in rule(s) variable assigned, assign variables[$1] (for example) , variable referenced, use $$ = variables[$1]; (for example). check n in $n correct value.
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