A Scanner to Count Lines and Characters

Here's another simple example:

    int num_lines = 0, num_chars = 0;

%%
\n    ++num_lines; ++num_chars;
.     ++num_chars;

%%
main()
    {
    yylex();
    printf( "# of lines = %d, # of chars = %d\n",
            num_lines, num_chars );
    }

This scanner counts the number of characters and the number of lines in its input (it produces no output other than the final report on the counts). The first line declares two globals, num_lines and num_chars, which are accessible both inside yylex and in the main routine declared after the second `%%'. There are two rules, one which matches a newline (`\n') and increments both the line count and the character count, and one which matches any character other than a newline (indicated by the `.' regular expression).