Yacc question related to %type

Hi to all!

I have made a yacc program example.y

Code:

---


%{

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/* #include "parser.h" */

%}

%start  program

%union {
                char *string;
                int integer;
                }


%token <string>  ID
%token <integer> NUMBER
%token <string> STRING
%token IF ELSE WHILE FOR
%token FUNCTION RETURN
%token TRUE FALSE NIL AND NOT OR

%left          '='
%left          "||"
%left          "&&"
%nonassoc        "==" "!="
%nonassoc      '>' ">=" '<' "<="
%left          '+' '-'
%left          '*' '/' '%'
%right          '!' "++" "--" UMINUS
%left          '.'

%%

program:        statements
                ;

statements:          statements stmt
                |
                ;

stmt:
                ';'
                |expr ';'
                |whilestmt
                |forstmt
                |returnstmt
                |block
                |funcdef
                |ifstmt
                ;

expression:
                assignexpr
                |expr '+' expr  { $$ = $1 + $3;} /*  HERE IS THE PROBLEM */
                |expr '-' expr
                |expr '*' expr
                |expr '/' expr  /*{ if($3==0)
                                                yyerror(.divide 0.);
                                          else
                                                $$ = $1 / $3;}                */
                |expr '%' expr
                |expr '>' expr
                |expr ">=" expr
                |expr '<' expr
                |expr "<=" expr
                |expr "==" expr
                |expr "!=" expr
                |expr "&&" expr
                |expr "||" expr
                ;


expr:          expression
                ;
%%


int main() {

}

---

Well in the example.y file we have the terminal symbols and non-terminal symbols
The terminal symbols i use are NUMBER,ID,STRING i have defined a type for them
e.g. ID has a string value, NUMBER has an integer value etc
Well i'm confused as far as the %type is concerned, We have to give a type to non terminals too.
If we do yacc example.y we take the output:

hello.y:58.36-37: $$ of `expression' has no declared type
hello.y:58.41-42: $1 of `expression' has no declared type
hello.y:58.46-47: $3 of `expression' has no declared type

This happens cause expression which is a non-terminal symbol has no type!

What type can this symbol take?shall i define a struct for this?

If i do : %type <integer> expression i take :

hello.y:61.18-30: warning: type clash on default action: <integer> != <>
hello.y:62.18-30: warning: type clash on default action: <integer> != <>
hello.y:63.18-30: warning: type clash on default action: <integer> != <>
hello.y:67.18-30: warning: type clash on default action: <integer> != <>
hello.y:68.18-30: warning: type clash on default action: <integer> != <>
hello.y:69.18-31: warning: type clash on default action: <integer> != <>
hello.y:70.18-30: warning: type clash on default action: <integer> != <>
hello.y:71.18-31: warning: type clash on default action: <integer> != <>
hello.y:72.18-31: warning: type clash on default action: <integer> != <>
hello.y:73.18-31: warning: type clash on default action: <integer> != <>
hello.y:74.18-31: warning: type clash on default action: <integer> != <>
hello.y:75.18-31: warning: type clash on default action: <integer> != <>

I would be glad if someone could help me!

Thanks in advance!!!

:)