foo.cc: In function 'int main()':
foo.cc:22:8: warning: statement has no effect [-Wunused-value]
  for (i; i < num; i++)
        ^
foo.cc:42:4: warning: 'j' may be used uninitialized in this function [-Wmaybe-uninitialized]
    if (j != -1)
    ^~

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