operating system操作系统 operator associativity运算符结合性 operator precedence运算符优先级 3.high- level language高级语言 low-evel language低级语言 assembly language汇编语言 4. retrieve检索2 operating system 操作系统 operator associativity 运算符结合性 operator precedence 运算符优先级 3. high-level language 高级语言 low-level language 低级语言 assembly language 汇编语言 4. retrieve 检索