foo.cc: In function 'int dfs(int, int)':
foo.cc:21:1: warning: no return statement in function returning non-void [-Wreturn-type]
   21 | }
      | ^
foo.cc: In function 'int main()':
foo.cc:31:25: warning: statement has no effect [-Wunused-value]
   31 |                 a[i][j] == 0;
      |                 ~~~~~~~~^~~~
foo.cc:38:8: warning: 'start_y' may be used uninitialized in this function [-Wmaybe-uninitialized]
   38 |     dfs(start_x, start_y);
      |     ~~~^~~~~~~~~~~~~~~~~~
foo.cc:38:8: warning: 'start_x' may be used uninitialized in this function [-Wmaybe-uninitialized]

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