511636_0_0_6769.cpp 511636_0_0_6769.cpp(5) : error C2065: “cin” : 未声明的标识符 511636_0_0_6769.cpp(6) : error C2065: “cout” : 未声明的标识符 511636_0_0_6769.cpp(6) : error C2065: “endl” : 未声明的标识符