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# 电子代写|编译器代写Compilers代考|CSC412 The Hierarchical Structure of Programming Languages

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## 电子代写|编译器代写Compilers代考|The Hierarchical Structure of Programming Languages

A programming language is a notation for specifying a sequence of operations to be carried out on data objects. Both the data objects and the operations can be grouped into a hierarchy that looks like the tree of Fig. 2.1. Not all languages have every one of these features, and some languages, such as ALGOL 68, permit statements to be in expressions. Nevertheless, the units in this hierarchy are so common that they should be familiar to all.

At the top of the hierarchy is the program itself. The program is the basic execution unit. Next comes an entity that can be compiled but not necessarily executed – the subroutine or block. These are units which may have their own data (local names). Subroutines differ from blocks by being callable from other portions of a program. Both subroutines and blocks are composed of statements. In turn, statements are fashioned from expressions, which are made up of operators, function calls, and references to data.

Having had this top-down view, we shall now study the hierarchy of elements bottom-up. Our intent is to build an understanding of each construct from an understanding of its constituent parts. The next section covers syntactic issues at all levels, with emphasis on the lowest levels, where they are most evident. The balance of the chapter will discuss semantic issues primarily.

## 电子代写|编译器代写Compilers代考|The Lexical and Syntactic Structure of a Language

Consider a string such as $A * B+C$. This string contains five symbols that can be grouped together in various ways. For example, this entire string might be considered to be one identifier. More likely, however, it would be considered to be three identifiers separated by two operators and interpreted as $(\mathrm{A} * \mathrm{~B})+\mathrm{C}$ or as $\mathrm{A} *(\mathrm{~B}+\mathrm{C})$. Which of these two is correct depends on the language definition. The lexical structure of a language determines what groups of symbols are to be treated as identifiers and operators. The syntactic structure determines how these lexical constructs are to be grouped together into larger structures called syntactic categories.
Alphabets
The set of symbols used in a programming language is called its character set or alphabet. As with natural languages, there is considerable variety in the alphabets of programming languages. The typical machine language usually has an alphabet of only 0 and 1 . Figure $2.2$ shows the alphabet sizes of some common programming languages.

.编译器

## MATLAB代写

MATLAB 是一种用于技术计算的高性能语言。它将计算、可视化和编程集成在一个易于使用的环境中，其中问题和解决方案以熟悉的数学符号表示。典型用途包括：数学和计算算法开发建模、仿真和原型制作数据分析、探索和可视化科学和工程图形应用程序开发，包括图形用户界面构建MATLAB 是一个交互式系统，其基本数据元素是一个不需要维度的数组。这使您可以解决许多技术计算问题，尤其是那些具有矩阵和向量公式的问题，而只需用 C 或 Fortran 等标量非交互式语言编写程序所需的时间的一小部分。MATLAB 名称代表矩阵实验室。MATLAB 最初的编写目的是提供对由 LINPACK 和 EISPACK 项目开发的矩阵软件的轻松访问，这两个项目共同代表了矩阵计算软件的最新技术。MATLAB 经过多年的发展，得到了许多用户的投入。在大学环境中，它是数学、工程和科学入门和高级课程的标准教学工具。在工业领域，MATLAB 是高效研究、开发和分析的首选工具。MATLAB 具有一系列称为工具箱的特定于应用程序的解决方案。对于大多数 MATLAB 用户来说非常重要，工具箱允许您学习应用专业技术。工具箱是 MATLAB 函数（M 文件）的综合集合，可扩展 MATLAB 环境以解决特定类别的问题。可用工具箱的领域包括信号处理、控制系统、神经网络、模糊逻辑、小波、仿真等。