foo.cc: In function 'int main()':
foo.cc:22:29: error: expected ']' before ';' token
   22 |             sum += arr[a - 1; ]
      |                             ^
      |                             ]
foo.cc:22:31: error: expected primary-expression before ']' token
   22 |             sum += arr[a - 1; ]
      |                               ^

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