0_0_24002121_25394.c 0_0_24002121_25394.c(3) : error C2065: “sum”: 未声明的标识符 0_0_24002121_25394.c(7) : error C2065: “sum”: 未声明的标识符 0_0_24002121_25394.c(12) : error C2065: “sum”: 未声明的标识符 0_0_24002121_25394.c(16) : error C2065: “sum”: 未声明的标识符