foo.cc: In function 'int abv(int)':
foo.cc:7:2: error: 'a' was not declared in this scope
    7 |  a
      |  ^
foo.cc:8:14: error: 'i' was not declared in this scope
    8 |  for(int i=1;i<=n;i++)
      |              ^
foo.cc:20:1: warning: no return statement in function returning non-void [-Wreturn-type]
   20 | }
      | ^

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