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与书有关的名言名句 Computer Language and Programming
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I. Introduction
Programming languages, in computer science, are the artificial languages ud to write a quence of instructions (a computer program) that can be run by a computer. Similar to natural languages, such as English, programming languages have a vocabulary, grammar, and syntax. However, natural languages are not suited for programming computers becau they are ambiguous, meaning that their vocabulary and grammatical structure may be interpreted in multiple ways. The languages ud to program computers must have simple logical structures, and the rules for their grammar, spelling, and punctuation must be preci.
Programming languages vary greatly in their sophistication and in their degree of versatility. Some programming languages are written to address a particular kind of computing problem or for u on a particular model of computer system. For instance, programming languages such as FORTRAN and COBOL were written to solve certain general types of pr
ogramming problems—FORTRAN for scientific applications, and COBOL for business applications. Although the languages were designed to address specific categories of computer problems, they are highly portable, meaning that they may be ud to program many types of computers. Other languages, such as machine languages, are designed to be ud by one specific model of computer system, or even by one specific computer in certain rearch applications. The most commonly ud programming languages are highly portable and can be ud to effectively solve diver types of computing problems. Languages like C, PASCAL and BASIC fall into this category.
II. Language Types
Programming languages can be classified as either low-level languages or high-level languages. Low-level programming languages, or machine languages, are the most basic type of programming languages and can be understood directly by a computer. Machine languages differ depending on the manufacturer and model of computer. High-level languages are programming languages that must first be translated into a machine langu南京历史
age before they can be understood and procesd by a computer. Examples of high-level languages are C, C++, PASCAL, and FORTRAN. Asmbly languages are intermediate languages that are very clo to machine languages and do not have the level of linguistic sophistication exhibited by other high-level languages, but must still be translated into machine language.
1. Machine Languages
In machine languages, instructions are written as quences of 1s and 0s, called bits, that a computer can understand directly. An instruction in machine language generally tells the computer four things: (1) where to find one or two numbers or simple pieces of data in the main computer memory (Random Access Memory, or RAM), (2) a simple operation to perform, such as adding the two numbers together, (3) where in the main memory to put the result of this simple operation, and (4) where to find the next instruction to perform. While all executable programs are eventually read by the computer in machine language, they are not all programmed in machine language. It is extremely di
fficult to program directly in machine language becau the instructions are quences of 1s and 0s. A typical instruction in a machine language might read 10010 1100 1011 and mean add the contents of storage register A to the contents of storage register B.
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2. High-Level Languages
High-level languages are relatively sophisticated ts of statements utilizing words and syntax from human language. They are more similar to normal human languages than asmbly or machine languages and are therefore easier to u for writing complicated programs. The programming languages allow larger and more complicated programs to be developed faster. However, high-level languages must be translated into machine language by another program called a compiler before a computer can understand them. For this reason, programs written in a high-level language may take longer to execute and u up more memory than programs written in an asmbly language.
3. Asmbly Languages
Computer programmers u asmbly languages to make machine-language programs easier to write. In an asmbly language, each statement corresponds roughly to one machine language instruction. An asmbly language statement is compod with the aid of easy to remember commands. The command to add the contents of the storage register A to the contents of storage register B might be written ADD B, A in a typical asmbly language statement. Asmbly languages share certain features with machine languages. For instance, it is possible to manipulate specific bits in both asmbly and machine languages. Programmers u asmbly
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languages when it is important to minimize the time it takes to run a program, becau the translation from asmbly language to machine language is relatively simple. Asmbly languages are also ud when some part of the computer has to be controlled directly, such as individual dots on a monitor or the flow of individual characters to a printer.
III. Classification of High-Level Languages
High-level languages are commonly classified as procedure-oriented, functional, object-oriented, or logic languages. The most common high-level languages today are procedure-oriented languages. In the languages, one or more related blocks of statements that perform some complete function are grouped together into a program module, or procedure, and given a name such as “procedure A.” If the same quence of operations is needed elwhere in the program, a simple statement can be ud to refer back to the procedure. In esnce, a procedure is just a
