0_0_20080786_28899.c 0_0_20080786_28899.c(12) : error C2065: “sum”: 未声明的标识符 0_0_20080786_28899.c(16) : error C2065: “sum”: 未声明的标识符 0_0_20080786_28899.c(19) : error C2065: “sum”: 未声明的标识符