foo.cc:84:6: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
 main()
      ^
foo.cc: In function 'int main()':
foo.cc:90:6: warning: ignoring return value of 'char* fgets(char*, int, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
 fgets(in,sizeof(in),stdin);
 ~~~~~^~~~~~~~~~~~~~~~~~~~~
foo.cc: In member function 'void expr::scan()':
foo.cc:65:6: warning: ignoring return value of 'char* fgets(char*, int, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
 fgets(t,sizeof(t),stdin);
 ~~~~~^~~~~~~~~~~~~~~~~~~

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