0_0_13688572_894.c 0_0_13688572_894.c(9) : error C2065: “sum”: 未声明的标识符 0_0_13688572_894.c(13) : error C2065: “sum”: 未声明的标识符 0_0_13688572_894.c(14) : error C2065: “sum”: 未声明的标识符