foo.cc: In function 'int main()':
foo.cc:4:12: warning: unused variable 'back' [-Wunused-variable]
    4 |  int m, n, back, g = 0 ;
      |            ^~~~
foo.cc:5:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
    5 |  scanf("%d %d", &m, &n);
      |  ~~~~~^~~~~~~~~~~~~~~~~
foo.cc:10:9: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   10 |    scanf("%d", &a[i][j]);
      |    ~~~~~^~~~~~~~~~~~~~~~

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