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1、 附件一 外文原文Object-Orientation and C+C+ is just one of many programming languages in use today. Why are there so many languages? Why do new ones appear every few years? Programming languages have evolved to help programmers ease the transition from design to implementation. The first programming langua
2、ges were very dependent on the underlying machine architecture. Writing programs at this level of detail is very cumbersome. Just as hardware engineers learned how to build computer systems out of other components, language designers also realized that programs could be written at a much higher leve
3、l, thereby shielding the programmer from the details of the underlying machine. Why are there such a large number of high-level programming languages? There are languages for accessing large inventory databases, formatting financial reports, controlling robots on the factory floor, processing lists,
4、 controlling satellites in real time, simulating a nuclear reactor, predicting changing atmospheric conditions, playing chess, and drawing circuit boards. Each of these problems requires different sets of data structures and algorithms. Programming languages are tools to help us solve problems. Howe
5、ver, there is not one programming language that is best for every type of problem. New programming languages are often developed to provide better tools for solving a particular class of problems. Other languages are intended to be useful for a variety of problem domains and are more general purpose
6、. Each programming language imparts a particular programming style or design philosophy on its programmers. With the multitude of programming languages available today, a number of such design philosophies have emerged. These design philosophies, called programming paradigms, help us to think about
7、problems and formulate solutions.1. Software Design through ParadigmsWhen designing small computer programs or large software systems, we often have a mental model of the problem we are trying to solve. How do we devise a mental model of a software system? Programming paradigms offer many different
8、ways of designing and thinking about software systems. A paradigm can be thought of as a mental model or as a framework for designing and describing a software systems structure. The model helps us think about and formulate solutions. We can use the mental model of a paradigm independently from the
9、programming language chosen for implementation. However, when the chosen language provides constructs and mechanisms that are similar to those that are found in the paradigm, the implementation will be more straightforward. Usually, there are several languages that belong to a paradigm. For this rea
10、son, a programming paradigm is also considered a class of languages. A language does not have to fit into just one paradigm. More often, languages provide features or characteristics from several paradigms. Hybrid languages, such as C+, combine characteristics from two or more paradigms. C+ includes
11、 characteristics from the imperative and procedural paradigms - just like its predecessor language, C - and the object-oriented paradigm.THE IMPERATIVE PARADIGM. The imperative paradigm is characterized by an abstract model of a computer with a large memory store. This is the classic von Neumann mod
12、el of computer architecture. Computations, which consist of a sequence of commands, are stored as encoding within the store. Commands enable the machine to find solutions using assignment to modify the store, variables to read the store, arithmetic and logic to evaluate expressions, and conditional
13、branching to control the flow of execution. THE PROCEDURAL PARADIGM. The procedural paradigm includes the imperative paradigm, but extends it with an abstraction mechanism for generalizing commands and expressions into procedures. Parameters, which are essentially aliases for a portion of the store,
14、 were also introduced by this paradigm. Other features include iteration, recursion, and selection. Most mainstreams programming today is done in a procedural language. The procedural paradigm was the first paradigm to introduce the notion of abstraction into program design. The purpose of abstracti
15、on in programming is to separate behavior from implementation. Procedures are a form of abstraction. The procedure performs some task or function. Other parts of the program call the procedure, knowing that it will perform the task correctly and efficiently, but without knowing exactly how the proce
16、dure is implemented. THE PROCEDURAL PARADIGM WITH ADTs.DATA ABSTRACTION is concerned with separating the behavior of a data object from its representation or implementation. For example, a stack contains the operations Push, Pop, and IsEmpty. A stack object provides users with these operations, but does not reveal how the stack is actually implemented. The stack could be implemented using an array o
