foo.cc: In function 'void Wangqiong(std::string&, int, int)':
foo.cc:6:14: warning: statement has no effect [-Wunused-value]
    6 |         for (l; s[l] != '\0'; l++)
      |              ^
foo.cc:8:12: warning: suggest explicit braces to avoid ambiguous 'else' [-Wdangling-else]
    8 |         if (si < l)
      |            ^

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