[BeginnerQuestion]Why I compile lex.yy.c failed?

Hi community,
I am a beginner who are interested in database,when I do my study on the lex and yacc,I write a example.l like this:

%%
.\|n ECHO
%%

and then I generate a lex.yy.c use lex
but when I compile this file,something wrong happend:

[beginnerc(at)bogon temp]$ flex '/home/beginnerc/work/temp/example.l'
[beginnerc(at)bogon temp]$ cc lex.yy.c -o first -ll
/home/beginnerc/work/temp/example.l: In function ‘yylex’:
lex.yy.c:619:28: error: expected ‘;’ before ‘break’
619 | #ifndef YY_BREAK
| ^
/home/beginnerc/work/temp/example.l:3:2: note: in expansion of macro ‘YY_BREAK’
3 | %%
| ^
[beginnerc(at)bogon temp]$

Can some one give me some suggestion?
Thanks in advance!
Yours,
JingZhang.