foo.cc: In function 'void check(std::string&)':
foo.cc:42:12: warning: suggest explicit braces to avoid ambiguous 'else' [-Wdangling-else]
   42 |         if ( b > 0) //如果左括号多了
      |            ^
foo.cc: In function 'int reduce(std::string)':
foo.cc:194:1: warning: control reaches end of non-void function [-Wreturn-type]
  194 | }
      | ^
foo.cc: In function 'int find(std::string)':
foo.cc:130:16: warning: 'k' may be used uninitialized [-Wmaybe-uninitialized]
  130 |         return k;
      |                ^
foo.cc:96:19: note: 'k' was declared here
   96 |         int i = 1,k;
      |                   ^

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