foo.cc:37:34: warning: multi-character character constant [-Wmultichar]
   37 |                         char L = '/0';//左括号
      |                                  ^~~~
foo.cc:38:34: warning: multi-character character constant [-Wmultichar]
   38 |                         char R = '/0';//右括号
      |                                  ^~~~
foo.cc: In member function 'void LinkStack::Match(char*)':
foo.cc:37:34: warning: overflow in conversion from 'int' to 'char' changes value from '12080' to ''0'' [-Woverflow]
   37 |                         char L = '/0';//左括号
      |                                  ^~~~
foo.cc:38:34: warning: overflow in conversion from 'int' to 'char' changes value from '12080' to ''0'' [-Woverflow]
   38 |                         char R = '/0';//右括号
      |                                  ^~~~
foo.cc:61:46: warning: unused variable 't' [-Wunused-variable]
   61 |                                         char t = pop();//出栈
      |                                              ^
foo.cc:37:30: warning: variable 'L' set but not used [-Wunused-but-set-variable]
   37 |                         char L = '/0';//左括号
      |                              ^
foo.cc:80:33: warning: unused variable 'a' [-Wunused-variable]
   80 |                         if (int a = empty() == true)
      |                                 ^

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