Файл: Н.Н. Курпешко Английский язык Методические указания для обучения студентов II курса (III семестр) специальности 180400.pdf

IV. Memorize the following word combinations:

master segment - главный сегмент; alphanumeric names - буквенно-

цифровые имена; data items - элементы данных; floating-point

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representation - представление с плавающей точкой (запятой); imaginary parts - мнимая часть (в комплексном числе); truth values - истинные значения; executable statements - исполнительные операторы; assign (ment) statements - операторы присвоения; dummy variables - фиктивные переменные; to meet the needs (requirements) - отвечать требованиям; default feature - признак «по умолчанию»; valid interpretation -

обоснованная интерпретация

TEXT D: HIGH LEVEL PROGRAMMING LANGUAGES:

FORTRAN AND PL/1

1.A high level language is a language in which each instruction or statement correspond to several machine code instructions It is contrasted with a low level language in which each instruction has a single corresponding machine code equivalent. High level languages allow users to write in a notation with which they are familiar, e. g., FORTRAN in mathematical notation, COBOL in English. So, high level languages are oriented to the problem, while low level languages are oriented to the machine code of a computer.

2.FORTRAN. FORTRAN is an acronym for FORmula TRANslation. It is a problem oriented high level programming language for scientific and mathematical use, in which the source program is written using a combination of algebraic formulae and English statements of a standard but readable form FORTRAN was the first high level programming language. It was developed in 1954, and was designed to easily express mathematical formulas for computer processing. It is still the most widely used programming language. There were several versions of FORTRAN. The most popular and used all over the world is FORTRAN-4.

3.A FORTRAN program consists of data items, executable statements and non-executable statements. The program is structured in segments which consist of a master segment and optional function segments and subroutines.

4.Data items in FORTRAN are either variables or constants, and ara assigned alphanumeric names by the programmer. Groups of similar items of data can be processed as arrays, or tables of data, in which case the individual items are defined by their position or reference within the array by naming the array followed by one or more subscripts.

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5. Data items in FORTRAN may take the following forms:

Integer is a whole number value falling within a range determined by the capacity of the computer being used. Real is a number expressed in floating-point representation accurate to a number of significant digits, the range again depends on the capabilities of the particular machine being used. Complex is a number in which two real numbers are used to express the real and imaginary parts. Logical is a quantity which can only take two values, true or false. Text is character information, which is not used for mathematical operations.

6.The actual operations of the program are expressed by means of 'executable statements'. These can take two forms: 'assignment statement' and 'control statement'. An assign statement takes the form Variable = Expression. The expression may be either arithmetic or logical. An arithmetic expression can include variables, elements, form arrays, constants and a variety of standard functions which are combined by arithmetic operators, e. g., +, -, '(multi-plication),/(division), (exponentiation). A logical expression is similar but include the operators AND, NOT, OR, etc., that is the logical operators.

7.An example of an arithmetic assignment statement would be.

ROOT = − B + B2 − 2AC , where the word ROOT and the letters А, В, С

2a

represent variables and SORT - the function provided for calculating square roots. The compiler recognizes these symbols and translates them into the appropriate machine code. An example of a logical assignment statement would be: BOOL-A. OR В. In this expression the variable BOOL would be given the value true or false according to the truth values of variables A and B, and the truth table defined by the Boolean operator OR.

8. Each statement can be preceded by a numerical label, permitting reference to the statement by means of control statements. Control statements enable the program to branch to other statements. Branches themselves may also be constructed which are conditional on results of arithmetic or logical operations.

9. As was said above, a FORTRAN program consists of one or more segments, of which there is one and only one master segment, and optionally, function and subroutine segments. A function segment is used where the same form of function is required several times in a program. The statements describing the operation required to calculate the result of using the function are named and written once, and whenever the function is

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required in the program1 it is only necessary to give the function name and a list of parameters to replace the 'dummy' variables used in the function segment.

10.PL/1. PL/1 was introduced in 1964. It was developed as a generalpurpose programming language, incorporating features from both COBOL and FORTRAN. PL/1 is used primarily on large mainframes. PL/1 stands for Programming Language 1. Commercial applications (COBOL) with their emphasis on efficient handling of large volumes of data have led to the development of languages with sophisticated I/O facilities; scientific problems (FORTRAN) with their emphasis on rapid definitions and descriptions of complex problems have led to the development of highly

sophisticated algorithmic languages while neglecting the data handling aspects.2

11.PL/1 aims at combining the problem-solving facility of scientific languages with the data-handling capabilities of commercial languages, in order to meet the needs of increasingly mathematical commercial analysis and increasingly large volumes of data being processed by scientific routines.

12.Among the more important features of PL/1 are the following: (1) The language is modular in structure. This means that the user needs only master the set of facilities necessary for his programming needs. More complex problems can use more extensive subsets of the language. (2) The language has a 'default' feature by which every error or unspecified option is given a valid interpretation, thus minimizing the effects of programming

errors. (3) The language structure is 'free form'. No special documents are needed for coding,3 since the significance of each statement depends on its own format and not on its position within a fixed framework.

13.PL/1 is much less sensitive to the peculiarities of the hardware than the machine language. This makes it possible to use the same program on different types of computers.

14.PL/1 uses 60 symbols: 29 letters from A to Z (capital Roman letters),4 10 digits from 0 to 9, and 21 special characters. The PL/1

statements are subdivided into the following logical groups:

input/output statements, declare statements,5 debugging statements,6 assignment statements, memory allocation statements,7 program structure statements, and control statements.

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Notes:

1.whenever the function is required in the program - всякий раз, когда

впрограмме требуется функция

2.while neglecting the data handling aspects - пренебрегая аспектами управления информацией

3.No special documents are needed for coding - никакие специальные документы для кодирования не требуются

4.capital Roman letters - заглавные латинские буквы

5.declare statements - операторы описания

6.debugging statements - операторы отладки

7.memory allocation statements - операторы распределения памяти

V. Memorize the following definitions:

1. FORTRAN is a problem oriented high level programming language for scientific and mathematical use. It is a compiler language. 2. PL/1 is a general-purpose high level programming language for scientific and commercial applications.

VI. Answer the following questions:

1. What is FORTRAN? 2. What are low level languages oriented to? 3. What are high level languages oriented to? 4. When was FORTRAN developed? 5. What does a FORTRAN program consist of? 6. Who assigns alphanumeric names to data items? 7. Which forms may data items in FORTRAN take? 8.. By means of what are the actual operations expressed in FORTRAN? 9. How is a program in FORTRAN structured? 10. What do segments in a FORTRAN program consist of?

VII. Compare FORTRAN and PL/1.

VIII. Speak on:

a)arithmetic and logical assignment statements in FORTRAN;

b)the features of the general-purpose PL/1.

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IX. Read Text 2 without a dictionary. Render the main points of the text in Russian:

2. ALGOL

ALGOL was developed as an international language for the expression of the algorithms between individuals, as well as a programming language. It was introduced in the early 1960s and gained popularity in Europe more than in the United States.

ALGOL is an acronym for ALGOrithmic Language. It is a problemoriented high level programming language for mathematical and scientific use, in which the source program provides a means of definite algorithms as a series of statements and declarations having a general resemblance (сходство) to algebraic formulae and English sentences.

3. HIGH LEVEL PROGRAMMING LANGUAGES: BASIC AND PASCAL

1.BASIC was developed in 1965 and stands for Beginners All-purpose Symbolic Instruction Code. It is a programming language designed for solving mathematical and business problems. BASIC was originally developed as an interactive programming language for timesharing on large mainframes. It is widely used on all sizes of computers and has become extremely popular on microcomputers.

2.There are many different versions of BASIC available with limited versions running on small hand-held computers. BASIC is available in both compiler and interpreter form, the latter form being more popular and easier to use, especially for the first-time programmer. In interpreter form the language is conversational and can be used as a desk calculator. In addition, it is easy to debug a program, since each line of code can be tested one at a time.

3.BASIC is considered to be one of the easiest programming languages to learn. For simple problems BASIC programs can be written 'on the fly', at the terminal. However, complex problems require programming technique, as in any conventional programming language. Since BASIC does not require a structured programming approach, like PASCAL, and since there is no inherent documentation in the language, as in COBOL, BASIC programs can be difficult to decipher later if the program was not coherently designed.

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4.BASIC is now used almost universally. There is no one BASIC language, but something like 90 different versions or dialects;

however, all have certain common features that make it easy to use any version once the fundamentals are mastered. Since BASIC is job and human oriented, it cannot be understood by the computer as written, but must go through the intermediate step of a compiler or interpreter, as was said above. As far as the programmer is concerned, it makes very little difference whether a compiler or interpreter is used.

5.A compiler, generally used in a large computer, converts the source program written in BASIC to an object program or file in machine language which is then stored in memory. In the compiler each BASIC phrase or statement is converted to one, or more machine instructions. An interpreter is similar in result, but conversion is usually done while the program is running, one statement at a time. The difference between the two, which is important to the microprocessor user, is that the interpreter must be preset in memory while the program is being run, while the compiler can be removed once it has done its job.

6.One would think then that a microcomputer would most often use a compiler, but this is not the case. Since interpreter programs can be run line- by-line, they can be debugged simply rather than being recompiled for each correction, and they are more popular in small computers. In certain versions the interpreter is stored in ROM, which is less expensive than RAM, and docs not need to be loaded from some external source such as a cassette.

7.The typical example of the algorithm in BASIC can be written as follows:

1.REM THIS PROGRAM SEARCHES A LIST AND PRINTS THE ADDRESS

10DATA 74, 83, 66, 67, 87, 65, 84, 80, 76, 70

20LET N = 10

30LET X = 65

40LET J = N

50IF J = 0 GOTO 100

60READ K

70IF К = GOTO 100

80LET J =] - 1

90GOTO 50

100PRINT J

110END