foo.cc: In function 'int main()':
foo.cc:14:2: error: 'a' was not declared in this scope
   14 |  a[0]=0;
      |  ^
foo.cc:40:7: warning: suggest explicit braces to avoid ambiguous 'else' [-Wdangling-else]
   40 |     if(vis[i])
      |       ^

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