Question

In the following code which is a lexical recognizer in C language:

    %{
#include <stdio.h>
void showToken(char*);
%}

%option yylineno
%option noyywrap
digit ([0-9])
letter ([a-zA-Z])
%%

letter(letter | digit)*             showToken("id");
(digit)(digit)*(.(digit)(digit)*)?      showToken("num");
[(),:;.]                printf("%c",yytext[0]); 
[ \n]
(==|<>|<|<=|>|>=)       showToken("relop");
(+|-)                   showToken("addop");
(*|/)                   showToken("mulop");
(=)                 showToken("assign");
(&&)                    showToken("and");
(||)                    showToken("or");
(!)                 showToken("not");
.                   {   
                    printf("Lexical Error");
                    exit(0);
                    }

%%
void showToken(char* name){
    printf("<%s,%s>",name,yytext);
}
%%

I get the following errors, why is that happening I think I wrote the code correctly!
I have done too many changes in the code but it doesn’t compile.

~/hedor>lex -t lexical.l > lexical.c
lexical.l:13: unrecognized rule
lexical.l:17: unrecognized rule
lexical.l:17: unrecognized rule
lexical.l:17: unrecognized rule
lexical.l:17: unrecognized rule
lexical.l:17: unrecognized rule
lexical.l:18: unrecognized rule
lexical.l:18: unrecognized rule
lexical.l:18: unrecognized rule
lexical.l:18: unrecognized rule
lexical.l:18: unrecognized rule
lexical.l:21: unrecognized rule
lexical.l:21: unrecognized rule
lexical.l:21: unrecognized rule
lexical.l:21: unrecognized rule

Answer 1

There are several issues in your regular expressions:

Line 13, actually the error is in the 12, do not add blanks in the RE, it breaks the expression and does not work as expected:

letter(letter|digit)*             showToken("id");

Line 17, the + is a special character, so escape it with \:

(\+|-)                   showToken("addop");

Line 18, the same with characters * and /:

(\*|\/)                   showToken("mulop");

Line 21, the same with |:

(\|\|)                    showToken("or");

That should fix the compilation errors, but note the comment by @JameySharp below, you likely want to write the digit and letter references using curly braces: {digit} and {letter}.