0_0_30307194_1464.cpp 0_0_30307194_1464.cpp(8) : error C2065: “cin”: 未声明的标识符 0_0_30307194_1464.cpp(8) : error C2065: “a”: 未声明的标识符 0_0_30307194_1464.cpp(10) : error C2065: “a”: 未声明的标识符