6、完成下面表達式的要求（共10分）
（1） if(x+y)*z=0 then s:=(a+b)*c else s:=a*b*c的逆波蘭式（后綴式）
（2）請將表達式 -(a+b)*(c+d)-(a+b)表示成四元式序列。
英語專業翻譯
只有一篇文章，內容如下：
A language is a system of communication. A programming language consists of all the symbols,characters,and usage rules that permit people to communicate with compters. Some programming languages are creted to serve a special purpose (e.g. controlling a robot),while others are more flexible general purpose tools that are suitain for many types of applications. However ,every programming language must accept certain types of written instructions. that will enable a computer system to perform a number of familiar operations.That is,every language must have instructions that fall into the following familiar categories:
(1) Input/output instrction. Required to permit commuication between I/O devices and the central processor, these instructions provide details on the type of input or output operation to be performed and the storage locations to be used during the operation to be performed and the storage locations to be used during the operation.
(2) Calculation instructions. instructions to permit addition, subtraction,multiplication,and division during proceing are, of course, common in all programming languages.
(3) Logic/comparison instruction. These instructions are used to transfer program control,and are needed in the selection and loop structures that are followed to prepare programs.
(4) Storage/retrieval and movement instructions. These instructions are used to store, retrieve, and move data during processing. data may be copied from one copied from one storage pocation to another and retrieved as needed.
But even though all programming languages have an instruction set that permits these familiar operations to be performed, there's a marked difference to be found in the symbols, characters , and synax of machine languages, assembly languages, and highlevel languages.