Operator is missing, for example, &quot; =2(3+4) * &quot; , where the operator between &quot; 2 &quot; and &quot; ( &quot; is missing.
缺少运算符，例如 &quot; =2(3+4) * &quot; ，其中 &quot; 2 &quot; 和 &quot; ( &quot; 之间缺少运算符。