ident_count.l

digit    [0-9]
letter   [A-Za-z]

%{
    int count;
%}

%%
    /* match identifier */
{letter}({letter}|{digit})*        count++;
%%

int yywrap(void) {
    return 1;
}

int main(void) {
    yylex();
    printf("number of identifiers = %d\n", count);
    return 0;
}