0_0_19837330_4772.c 0_0_19837330_4772.c(18) : error C2065: “sum”: 未声明的标识符 0_0_19837330_4772.c(22) : error C2065: “sum”: 未声明的标识符 0_0_19837330_4772.c(23) : error C2065: “sum”: 未声明的标识符