foo.cc: In function 'int main()':
foo.cc:24:7: warning: unused variable 'f' [-Wunused-variable]
   24 |  bool f;
      |       ^
foo.cc:26:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   26 |  scanf("%d%d",&m,&n);
      |  ~~~~~^~~~~~~~~~~~~~
foo.cc:30:9: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   30 |    scanf("%d",&a[i][j]);
      |    ~~~~~^~~~~~~~~~~~~~~

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