foo.cc: In function 'int main()':
foo.cc:14:2: error: expected ';' before 'for'
  for(int i=1;i<=n;i++)
  ^~~
foo.cc:14:14: error: 'i' was not declared in this scope
  for(int i=1;i<=n;i++)
              ^
foo.cc:16:3: error: 'else' without a previous 'if'
   else b[n+1-i/2]=a[i];
   ^~~~

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