Qfyilyi

I want to create a programming language consisting multiple character variables (e.g. abc=10, num=120). I was able to create single character variable . The .y code is :

%{

    #include <stdio.h>

                  //char sym[1000];

    //int x=0;

    int sym[26];



%}





%token NUMBER ADD SUB MUL DIV ABS EOL ID ASS

%%

calclist : 

    | calclist exp EOL   { printf("= %dn", $2); } 

    | ID ASS exp EOL     { sym[$1] = $3;



             }

;

exp:    factor           { $$=$1; }

    | exp ADD factor     { $$ = $1 + $3; }

    | exp SUB factor     { $$ = $1 - $3; }

;

factor :    term         { $$=$1; }

    | factor MUL term    { $$ = $1 * $3; }

    | factor DIV term    { $$ = $1 / $3; }

;

term :  NUMBER       { $$=$1; }



;



%%

int main(int argc, char **argv)

{

yyparse();

}

yyerror(char *s)

{

fprintf(stderr, "error: %sn", s);

} 

and the .l code is :

%{

# include "P3.tab.h"

#include <stdio.h>

#include <stdlib.h>

extern int yylval;

//int m=0;

%}



%%

"+"     { return ADD; }

"-"     { return SUB; }

"*"  { return MUL; }

"/"     { return DIV; }

"=" { return ASS; }

[a-z]+  { yylval= *yytext  - 'a' ;  

     return ID ; }

[0-9]+  { yylval = atoi(yytext); return NUMBER; }

n   { return EOL; }

[ t]   { /* ignore whitespace */ }

.    { printf("Mystery character %cn", *yytext); }

%%

int yywrap()

{

return 1;

}

So, with this code , I can only create a=10,x=90 kind of single character variable . How can I create multiple character variable And I also want to check if it is already declared or not ?

This has very little to do with bison or flex. In fact, your flex patterns already recognise multi-character identifiers (as long as they are purely alphabetic), but the action ignores characters after the first.

What you need is some kind of associative container like a hash table, which you could use as a symbol table instead of the vector sym.

The Bison manual includes a number of small example calculator programs. See, for example, mfcalc, which includesa symbol table implemented as a simple linear association list.