指针有效运算 相同类型指针之间的赋值运算 指针同整数之间的加法减法运算 指向同一个数组中元素的两个指针间的减法或比较运算 指针赋值0或与0（NULL）的比较运算 front end scanning (source code to tokens) parsing (tokens to ast) semantic analysis (types match) optimizer common subexpress elimatation (cse) back end register allocation (mapping virtual registers into physic registers) instruction scheduling (reorder instructions to reduce execution cycles) instruction selection 运算符优先级：决定不同运算符之间如何优先执行，结合性：决定相同运算符之间如何优先执行。 Name Operators Associates Equality == != Left Comparison > >= < <= Left Term - + Left Factor / * Left Unary ! - Right