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设有Pascal程序： program p_7_6 var a，b，c：integer； L1：procedure pl(var z：integer) var a，x，y：integer； b：array[1．．5，1．．io]of real； function f(var t：integer)：boolean； var x：integer； L2： begin X：=a+t； f：=x+2 end； begin
end； L4：procdure p2(var y：integer)； var x，z：real； begin
end； begin
L7： end． 试用图示法说明，在程序执行过程中，当控制到达各标号处时数据空间栈的存储分配情况。
答案
更多“设有Pascal程序： program p_7_6 var a，b，c：integer； L1：procedure pl（var z：inte”相关的问题
第1题
对下面的Pascal程序： PROGRAM ex710； VAR k：Real； FUNCTION f(n：Integer)：Real； BEGIN IF n＝0 THEN f：＝1 ELSE f：＝n*f(n－1) END； BEGIN k：＝f(10)； Write(k) END． 试指出：当递归调用函数f(n)时，在第二次进入f之后，栈式存储分配活动记录的内容是什么？
第2题
Assembly Language
汇编语言
Introducing Assembly Language
Assembly language unlocks the secrets of your computer's hardware and software[1]. It teaches you about the way the computer's hardware and operating system work together and how application programs communicate with the operating system.
To understand a computer and it.s operating system fully, one needs to study software at various levels. One is the application program level, where such programs interact with DOS. Another is the high-level language level, where powerful statements are expanded into many machine instructions recognized directly by CPU (Central Processing Unit), as well as the way programs communicate with DOS.
What Is Assembly Language？
Assembly language is a programming language with a one-to-one correspondence between its statements and a computer's machine language. There is no single assembly language because there is no single type of computer CPU. Each assembly language is directly influenced by a computer's machine instruction set and hardware architecture.
Strictly speaking, IBM-PC assembly language refers to instructions recognized by the intel 8086-80486(CPU) microprocessor family. But there is such close interaction between the CPU, computer peripherals, the DOS operating system, and the macro assembler itself that our discussions will often include all these topics.
What Is An Assembler？
An assembler is a program that converts source-code programs into machine language. In this passage, we will refer to an assembler that generates machine instructions for IBM- compatible microcomputers. All such computers use the Intel family of microprocessors, beginning with the Intel 8088, through the Intel 80486 (and beyond). Our programs will run under the PC-DOS/MS-DOS operating system, version 3. 0 or later. The two best- known assemblers for the IBM-PC are MASM (Microsoft Assembler) and TASM (Borland Turbo Assembler).
Assembly language is a specific set of instructions for a particular computer system. It provides a direct correspondence between symbolic statements and machine language. An assembler is a program that translates a program written in assembly language into machine language, which may in turn be executed by the computer. Each type of computer has a different assembly language, because the computer's design influences the instructions it can execute.
Assembly language is called a low-level language because it is close to machine language in structure and function. We can say that each assembly language instruction corresponds to one machine instruction. In contrast, high-level languages such as Pascal[2], BASIC[3], FORTRAN[4], and COBOL[5]contain powerful statements that are translated into many machine instructions by a compiler.
Why Learn Assembly Language？
People learn assembly language for various reasons. The most obvious one may be to learn about the computer's architecture and operating system. You may want to learn more about the computer you work with and about the way languages generate machine code. Because of assembly language's close relationship to machine language, it is closely tied to the computer's hardware and software.
You may also want to learn assembly language for its utility. Certain types of programming are difficult or impossible to do in high-level language. For example, direct communication with the computer's operating system may be necessary. A high-speed color graphics program may have to be written using a minimum of memory space. A special program may be needed to interface a printer to a computer. Perhaps you will need to write a telecommunications program for the IBM-PＣ. Clearly, the list of assembly language applications is endless.
Often there is a need to remove restrictions. High-Ievel languages, out of necessity, impose rules about what is allowed in a program. For example, Pascal does not allow a character value to be assigned to an integer variable.[6] This makes good sense unless there is a specific need to do just that. An experienced programmer will find a way around this restriction or rule; nearly everything is left to the discretion of the programmer. The price for such freedom is the need to handle many details that would otherwise be taken care of by the programming language itself.
Assembly language's usefulness as a learning tool should not be underestimateＤ. By having such intimate contact with the operating system, assembly language programmers come to know instinctively is how the operating system works. This knowledge, coupled with knowledge of hardware and data storage, gives them a tremendous advantage when tackling unusual programming problems. They have a different viewpoint than programmers who know only high-level language.
Assembly Language Applications
At first, the assembly language programs presented later will seem almost trivial. Those new to assembly language often cannot believe the amount of work required to perform relatively simple tasks. The language requires a great deal of attention to detail. Most programmers don't write large application programs in assembly language. Instead, they write short, specific routines.
Often we write subroutines in assembly language and call them from high-level language programs. You can take advantage of the strengths of the high-level languages by using them to write applications. Then you can write assembly language subroutines to handle operations that are not available in the high-level language.
Suppose you are writing a business application program in COBOL for the IBM-PＣ. You then discover that you need to check the free space on the disk, create a subdirectory, write a file, and create overlapping windows, all from within the program. Assuming that your COBOL compiler does not do all this, you can then write assembly language subroutines to handle these tasks.
Let's use another example: you might have written a word processing program in C[7]or Pascal, but it performs slowly when.updating the screen display. If you knew how, you could write routines in assembly language to speed up critical parts of the application and allow the program to perform up to professional standards.
Large application programs written purely in assembly language, however, are beyond the scope of the person who has just finished this book. There are many people who write complete assembly language application program for the IBM-PＣ. The few programmers in this group are familiar with several machine architectures and assemblers, and have been programming professionally for at least several years. These fortunate individuals still had to start with a basic foundation, and this book is intended to help you acquire just that.
Above all, assembly language programmers must know their date, for without a detailed understanding of how each date type is stored(at the bit level) , one might make serious mistakes. High-Ievel programming languages intentionally shield programmers from implementation-specific details, in the name of convenience and source-code portability. Assembly language, in contrast, is highly machine-specific and imposes few, if any, restrictions.
Machine Language
Before we embark on a rather long and detailed study of assembly language, let's put it into perspective. A computer doesn't actually understand assembly language-it understands machine language. Machine language is a language made up of numbers, which can be interpreted by a computer's CPU. A CPU usually has a small program embedded directly in the chip, called microcode. The microcode interpreter translates machine instructions directly into hardware signals.
Machine language makes it possible for the CPU to perform ordinary tasks, such as moving numbers or performing arithmetiＣ. Each CPU has its own machine language; or, in the case of IBM-compatible computers, all CPUs that belong to the intel family (8088, 8086,80186,80286,80386,80486) share a common machine language. This is an example of a machine language instruction that moves 5 into the AL register: 10110000 00000101. The number is written in binary, a number system made up of only the digits 1 and 0. The first 8 bits are the operation code (op code), which identifies it as the instruction that moves an 8-bit number to the AL register. The second 8 bits are the operand[8]. The complete instruction moves the number 5 to a register called AL. Registers are high-speed storage locations inside the CPU. They are identified by two-letter names, such as AH, AL, or AX.
A CPU's instructions set is the set of machine instruciions that the CPU is able to execute. For the Intel CPU family, the instruction set is downward-compatible, meaning that an instruction that works on a lower-level processor will always work on a higher-level processor. For example, the MOV instruction[9]works on the 8088, and therefore must work on the 80286. But there are many advanced instructions for the 80286 that do not work on the 8088.
At one time, all programs were written in machine language. But it's easy to see that machine instructions are difficult for humans to read and write. This is why assemblers and compilers were created, which would convert more readable instructions, created by a text editor, into machine language. Instead of writing the machine instruction shown earlier, we would write the following in assembly language:
M o v ah, 5
Notes
[1]unlocks the secrets：揭开了……奥秘。
[2]Pascal(Philips Automatic Sequence Calculator)：菲利浦自动顺序计算机语言。
[3]Basic(Beginner's All-purpose Symbolic Instruction Code)：初学者通用符号指令码。
[4]Fortran(Formula Translator)：公式翻译程序设计语言，FORTRAN语言。
[5]COBOL(Common Business-Oriented Language)：面向商业的通用语言，COBOL语言。
[6]For example，Pascal does not allow a character value to be assigned to an integer variable．例如，Pascal语言就不允许给一个整变量赋予字符值。
[7]C：C语言，一种高级程序设计语言，由贝尔实验室开发成功。
[8]Operand：操作数；运算数。
[9]Mov instruction：数据传输指令。
Say whether the following is true or not:
第4题
A.PROgram
B.PROGRAM
C.PRO
D.proGRAM
第5题
Computer Languages
计算机语言
A computer must be given instructions in a language that it understands, that is, a particular pattern of binary digital information. On the earliest computers, programming was a difficult, laborious task, because vacuum tube ON/OFF switches had to be set by hand. Teams of programmers often took days to program simple tasks, such as sorting a list of names. Since that time a number of computer languages have been devised, some with particular kinds of functioning in mind and others aimed more at ease of use-the user-friendly approach.
Machine Language
Unfortunately, the computer's own binary based language, or machine language, is difficult for humans to use. The programmer must input every command and all data in binary form, and a basic operation such as comparing the contents of a register to the data in a memory chip location might look like this: 11001010 00010111 11110101 00101011. Machine language programming is such a tedious, time-consuming task that the time saved in running the program rarely justifies the days or weeks needed to write the program.
Assembly Language
One method programmers devised to shorten and simplify the process is called assembly language programming. By assigning a short (usually three letter) mnemonic code to each machine language command, assembly language programs could be written and-debugged-cleaned of logic and date errors-in a fraction of the time needed by machine language programmers. In assembly language, each mnemonic command and its symbolic operands equals one machine instruction. An assembler program translates the mnemonic opcodes (operation codes) and symbolic operands into binary language and executes the program. Assembly language is a type of low level computer programming language in which each statement corresponds directly to a single machine instruction. Assembly languages are, thus, specific to a given processor. After writing an assembly language program, the programmer must use the assembler language into machine code. Assembly language provides precise control of the computer, but assembly language programs written for one type of computer must be rewritten to operate on another type. Assembly language might be used instead of a high levcl language for any of three major reasons: speed, control, and preference. Programs written in assembly language usually run faster than those generated by a compiler; use of assembly language lets a programmer interact directly with the hardware (processor, memory, display, and input/output ports). Assembly language, however, can be used only with one type of CPU chip or microprocessor. Programmers who expended much time and effort to learn how to program one computer had to learn a new programming style each time they worked on another machine. What was needed was a shorthand method by which one symbolic statement could represent a sequence of many machine language instructions, and a way that would allow the same program to run on several types of machines. These needs led to the development of so-called high level languages.
High Level Languages
High level languages often use English-Iike words-for example, LIST, PRINT, OPEN, and so on-as commands that might stand for a sequence of tens or hundreds of machine language instructions. The commands are entered from the keyboard or from a program in memory or in a storage device, and they are interpreted by a program that translates them into machine language instructions.
Translator programs are of two kinds: interpreters and compilers. With an interpreter, programs that loop back to reexecute part of their instructions reinterpret the same instructions each time it appears, so interpreted programs run much more slowly than machine language programs. Compilers, by contrast, translate an entire program into machine language prior to execution, so such programs run as rapidly as though they were written directly in machine language.
American computer scientist Grace Hopper is credited with implementing the first commercially oriented computer language. After programming an experimental computer at Harvard University[1], she worked on the UNIVAC[2]I and II computers and developed a commercially usable high level programming language called FLOW MATIC to facilitate computer use in scientific applications. IBM[3]then developed a language that would simplify work involving complicated mathematical formulas. Begun in 1954 and completed in 1957, FORTRAN (FORmula TRANslator)[4]was the first comprehensive high level programming language that was widely used. In 1957, the Association for Computing Machinery[5]set out to develop a universal language that would correct some of FORTRAN' s perceived faults. A year later, they released ALGOL[6](ALGOrithmic Language), another scientifically oriented language; widely used in Europe in the 1960s and 1970s, it has since been superseded by newer languages, while FORTRAN continues to be used because of the huge investment in existing programs. COBOL[7](COmmon Business Oriented Language), a commercial and business programming language, concentrates on data organization and file handling and is widely used today in business.
BASIC[8](Beginners All-purpose Symbolic Instruction Code) was developed at Dartmouth College in the early 1960s for use by nonprofessional computer users. The language came into almost universal use with the microcomputer explosion of the 1970s and 1980s. Condemned as slow, inefficient, and inelegant by its detractors, BASIC is nevertheless simple to learn and easy to use. Because many early microcomputers were sold with BASIC built into the hardware (in ROM memory) the language rapidly came into widespread use. As a very simple example of a BASIC program, consider the addition of the numbers 1 and 2, and the display of the result. This is written as follows (the numerals 10-40 are line numbers):
10 A=1
20 B=2
30 C=A+B
40 PRINT C
Although hundreds of different computer languages and variants exist, several others deserve mention. PASCAL[9], originally designed as a teaching tool, is now one of the most popular microcomputer languages. LOGO was developed to introduce children to computers. C, a language Bell Laboratories designed in the 1970s, is widely used in developing systems programs, such as language translators. LISP[10]and PROLOG are widely used in artificial intelligence.
COBOL
COBOL, in computer science, acronym for COmmon Business-oriented language, is a verbose, English-like programming language developed between 1959 and 1961. Its establishment as a required language by the U. S. Department of Defense, its emphasis on data structures. and its English-like syntax (compared to those of FORTRAN and ALGOL) led to its widespread acceptance and usage, especially in business applications. Programs written in COBOL, which is a compiled language, are split into four divisions: Identification, Environment, Data, and Procedure. The Identification division specifies the name of the program and contains any other documentation the programmer wants to add. The Environment division specifies the computer(s) being used and the files used in the program for input and output. The Data division describes the data used in the program. The Procedure division contains the procedures that dictate the actions of the program.
C & C++
A widely used programming language, C was developed by Dennis Ritchie at Bell Laboratories in 1972; it was so named because its immediate predecessor was the B programming language. Although C is considered by many to be more a machine independent assembly language than a high level language, its close association with the UNIX[11]operating system, its enormous popularity, and its standardization by the American National Standards Institute (ANSl)[12]have made it perhaps the closest thing to a standard programming language in the microcomputer/workstation marketplace. C is a compiled language that contains a small set of built in functions that are machine dependent. The rest of the C functions are machine independent and are contained in libraries that can be accessed from C programs. C programs are composed of one or more functions defined by the programmer; thus, C is a structured programming language. C+ +, in computer science, is an object oriented version of the C programming language, developed by Bjarne Stroustrup in the early 1980s at Bell Laboratories and adopted by a number of vendors, including Apple Computer, Sun Microsystems, Borland International, and Microsoft Corporation.
Notes
[1]Harvard University：美国哈佛大学。
[2]UNIVAC(Universal Automatic Computer)：通用自动计算机。
[3]IBM(International Business Machine Corp)：国际商用机器公司。
[4]FORTRAN(FORmula TRANslator)：公式翻译程序设计语言。
[5]the Association for Computing Machinery：计算机协会(美国)。
[6]ALGOL(ALGOrithmic Language)：面向代数的语言。
[7]COBOL(Common Business Oriented Language)：面向商业的通用语言。
[8]BASIC(Beginners All-purpose Symbolic Instruction Code)：初学者通用符号指令码。
[9]PASCAL(Philips Automatic Sequence Calculator)：菲利浦自动顺序计算机语言。
[10]LISP(List Process)：表处理程序，或表处理语言。
[11]UNIX(Uniplexed Information and Computer Systems)：UNIX操作系统，1969年在
AT&T Bell实验室开发的多用户多任务操作系统。
[12]ANSI(American National Standards Institute)：美国国家标准学(协)会。
第6题
下面程序的输出结果是【 】。 include＜stdio.h＞ main() { static char a[]=" language" ,b[]=" program"; char *ptr1=a, *ptr2=b; int k; for(k=0;k＜7;k++) if(*(ptr1+k)==*(ptr2+k)) printf(" %c",*(ptr1+k)); }
第7题
以下程序运行后输出______。 include ＜stdio.h＞ int f(char*s1,char*s2) { static int n1,n2； while(*s1++)n1++； while(*s2++)n2++； return n1-n2； } main() { printf("%d"，f("c：\\program","\12a\t34\n"))；}
第8题
第9题
二部图(biparite graph)G=(V，E)是一个能将其结点集V分为两个不相交子集V1和V2= V-V1的无向图，使得：V1中的任何两个结点在图G中均不相邻，V2中的任何两个结点在图G中也均不相邻。 (1)请各举一个结点个数为5的二部图和非二部图的例子。 (2)请用C或Pascal编写一个函数BIPARTITE判断一个连通无向图G是否是二部图，并分析程序的时间复杂度。设G用二维数组A来表示，大小为n*n(n为结点个数)。请在程序中加必要的注释。若有必要可直接利用堆栈或队列操作。【浙江大学1998
第10题
Evolution of Computer Architecture
计算机体系的演变
The study of computer architecture involves both hardware organization and programming/software requirements. As seen by an assembly language programmer, computer architecture is abstracted by its instruction set, which includes operation codes (opcode for short), addressing modes, registers, virtual memory, etc.
Legends:
I/E: Instruction Fetch and Execute
SIMD: Single Instruction Streams and Multiple Data Streams
MIMD: Multiple Instruction Streams and Multiple Data Streams Figure 1Tree Showing Architectural Evolution from Sequential Scalar Computers to Vector Processors and Parallel Computers
From the hardware implementation point of view, the abstract machine is organized with CPUs, caches, buses, microcodes, pipelines, physical memory, etc. Therefore, the study of architecture covers both instruction-set architectures and machine implementation organizations.
Over the past four decades, computer architecture has gone through evolutional rather than revolutional changes. Sustaining features are those that were proven performance deliverers, we started with the Von Neumann architecture[1]built as a sequential machine executing scalar data. The sequential computer was improved from bit-serial to word- parallel operations, and from fixed-point to floating-point operations. The Von Neumann architecture is slow due to sequential execution of instructions in programs.
Lookahead, Parallelism and Pipelining[2]
Lookahead techniques were introduced to prefetch instructions in order to overlap I/E (instruction fetch/decode and execution)[3]operations and to enable functiorial parallelism. Functional parallelism was supported by two approaches: One is to use multiple functional units simultaneously, and the other is to practice pipelining at various processing levels.
The latter includes pipelined instruction execution, pipelined arithmetic computations, and memory-access operations. Pipelining has proven especially attractive in performing identical operations repeatedly over vector data strings. Vector operations were originally carried out implicitly by software-controlled looping using scalar pipeline processors.
Flynn's Classification[4]
Flynn introduced a classification of various computer architectures based on notions of instruction and data streams in 1972. Conventional sequential machines are called SISD (single instruction stream over a single data stream)[5]computers. Vector computers are equipped with scalar and vector hardware or appear as SIMD (single instruction stream over multiple data streams)[6]machines. Parallel computers are reserved for MIMD (multiple Instruction streams over multiple data streams)[7]machines.
An MISD (multiple instruction streams and a single data steam)[8]machines are modeled. The same data stream flows through a linear array of processors executing different instruction streams. This architecture is also known as systolic arrays for pipelined execution of specific algorithms.
Of the four machine models, most parallel computers built in the past assumed the MIMD model for general-purpose computations. The SIMD and MISD models are more suitable for special-purpose computations. For this reason, MIMD is the most popular model, SIMD next, and MISD the least popular model being applied in commercial machines.
Parallel Computers
Intrinsic parallel computers are those that execute programs in MIMD mode. There are two major classes of parallel computers, namely, shared-memory multiprocessors and message-passing multicomputers. The major distinction between multiprocessors and multicomputers lies in memory sharing and the mechanisms used for interprocessor communication.
The processors in a multiprocessor system communicate with each other through shared variables in a common memory. Each computer node in a multicomputer system has a local memory, unshared with other nodes. Interprocessor communication is done through message passing among the nodes.
Explicit vector instructions were introduced with the appearance of vector processors. A vector processor is equipped with multiple vector pipelines that can be concurrently used under hardware or firmware control. There are two families of pipelined vector processors.
Memory-to-memory architecture supports the pipelined flow of vector operands directly from the memory to pipelines and then back to the memory. Register-to-register architecture uses vector registers to interface between the memory and functional pipelines.
Another important branch of the architecture tree consists of the SIMD computers for synchronized vector processing. An SIMD computer exploits spatial parallelism rather than temporal parallelism as in a pipelined computer. SIMD computing is achieved through the use of an array of processing elements synchronized by the same controller. Associative memory can be used to build SIMD associative processors.
Development Layers
Hardware configurations differ from machine to machine, even those of the same model. The address space of a processor in a computer system varies among different architectures. It depends on the memory organization, which is machine-dependent. These features are up to[9]the designer and should match the target application domains.
On the other hand, we want to develop application programs and programming environments which are machine-independent. Independent of machine architecture, the user programs can be ported to many computers with minimum conversion costs. High- level languages and communication models depend on the architectural choices made in a computer system. From a programmer's viewpoint, these two layers should be architecture-transparent.
At present, Fortran, C, Pascal, Ada, and Lisp[10]are supported by most computers. However, the communication models, shared variable versus message passing, are mostly machine-dependent. The Linda approach using tuple spaces offers any architecture- transparent communication model for parallel computers.
Application programmers prefer more architectural transparency. However, kernel programmers have to explore the opportunities supported by hardware. As a good computer architect, one has to approach the problem from both ends. The compilers and OS support should be designed to remove as many architectural constraints as possible from the programmer.
New Challenges
The technology of parallel processing is the outgrowth of four decades of research and industrial advances in microelectronics, printed circuits, high-density packaging, advanced processors, memory systems, peripheral devices, communication channels, language evolution, compiler sophistication, operating systems, programming environments, and application challenges.
The rapid progress made in hardware technology has significantly increased the economical feasibility of building a new generation of computers adopting parallel processing. However, the major barrier preventing parallel processing from entering the production mainstream is on the software and application side.
To date, it is still very difficult and painful to program parallel and vector computers[11]. We need to strive for major progress in the software area in order to create a user-friendly environment for high-power computers. A whole new generation of programmers need to be trained to program parallelism effectively. High-performance computers provide fast and accurate solutions to scientific, engineering, business, social, and defense problems.
Representative real-life problems include weather forecast modeling, computer-aided design of VLSI[12]circuits, large-scale database management, artificial intelligence, crime control, and strategic defense initiatives, just to name a few. The application domains of parallel processing computers are expanding steadily. With a good understanding of scalable computer architectures and mastery of parallel programming techniques the reader will be better prepared to face future computing challenges.
Notes
[1] the Von Neumann architecture: 冯·诺依曼体系结构，由匈牙利科学家Von Neumann于1946年提出。其基本思想是“存储程序”的概念，即把程序与数据存放在线性编址的存储器中，依次取出，进行解释和执行。
[2] Lookahead, Parallelism and Pipelining: 先行(预见)、并行性和流水线技术(管线)。
[3] I/E (instruction fetch/decode and execution)：取指令(指令去还)。
[4] Flynn Classification：弗林分类法，M.J. 弗林于1966年提出的、根据系统的指令和数据对计算机系统进行分类的一种方法。
[5] SISD(single instruction stream over a single data stream)：单指令单数据流(或single instruction single data).
[6] SIMD (single instruction stream over multiple data streams)：单指令多数据流(或single instruction multiple data).
[7] MIMD (multiple Instruction streams over multiple data streams)：多指令多数据流(或multiple Instruction multiple data).
[8] MISD (multiple instruction streams and a single data steam)：多指令单数据流(或multiple instruction single data).
[9] up to：应由某人担任或负责。如：It is up to them to decide. 应由他们决定。这一句可译为“这些特性由设计者考虑决定”。
[10] Fortran, C, Pascal, Ada, and Lisp: (分别是)Fortran语言、C语言、Pascal语言、Ada语言和Lisp语言。
[11] vector computers：向量计算机；向量电脑；一种数组计算机(an array computer)。
[12] VLSI: very large scale integration超大规模集成电路；大规模积体电路。
第11题
设有如下程序： Private Sub Form_Click() a=325456 Print Format(Int((a*10+0.5))/10，"000，000.00") End Sub 程序运行后，单击窗体，输出结果为【 】。
