foo.cc: In function ‘void dfs(int, int)’:
foo.cc:11:16: warning: statement has no effect [-Wunused-value]
   11 |         a[x][y]==0;
      |         ~~~~~~~^~~
foo.cc: In function ‘int main()’:
foo.cc:25:24: warning: statement has no effect [-Wunused-value]
   25 |                 a[i][j]==1;
      |                 ~~~~~~~^~~
foo.cc:27:21: warning: statement has no effect [-Wunused-value]
   27 |         else a[i][j]==0;
      |              ~~~~~~~^~~