No Error:
ImplicitCastExpr 0x807d7f178 '_Bool' <IntegralToBoolean>
`-BinaryOperator 0x807d7f118 'int' '=='
  |-OffsetOfExpr 0x807d7f0a8 'unsigned long'
  `-ImplicitCastExpr 0x807d7f100 'unsigned long' <IntegralCast>
    `-IntegerLiteral 0x807d7f0e0 'int' 4

Error:
ImplicitCastExpr 0x807d7f5e8 '_Bool' <IntegralToBoolean>
`-BinaryOperator 0x807d7f588 'int' '=='
  |-OffsetOfExpr 0x807d7f468 'unsigned long'
  `-ImplicitCastExpr 0x807d7f570 'unsigned long' <IntegralCast>
    `-ImplicitCastExpr 0x807d7f558 'int' <LValueToRValue>
      `-ArraySubscriptExpr 0x807d7f530 'const int' lvalue
        |-ImplicitCastExpr 0x807d7f518 'const int *' <ArrayToPointerDecay>
        | `-DeclRefExpr 0x807d7f4a0 'const int [2]' lvalue Var 0x807d7f248 'offsets' 'const int [2]'
        `-IntegerLiteral 0x807d7f4c8 'int' 0