Programming





A program is a sequence of instructions that tells the hardware of a computer what operations to perform on data. Programs can be built into the hardware itself, or they may exist independently in a form known as software. In some specialized, or dedicated computers the operating instructions are embedded in their circuitry; common examples are the microcomputers found in calculators, wristwatches, automobile engines, and microwave ovens. A general purpose computer, on the other hand, contains some built-in programs (in ROM) or instructions (in the processor chip), but it depends on external programs to perform useful tasks. Once a computer has been programmed, it can do only as much or as little as the software controlling it at any given moment enables it to do. Software in widespread use includes a wide range of applications programs-instructions to the computer on how to perform various tasks. Languages. A computer must be given instructions in a language that it understands-that is, a particular pattern of binary digital information. Unfortunately, the computer's own binary-based language, or machine language, is difficult for humans to use. 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 data errors-in a fraction of the time needed by machine-language programmers. 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-like 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 intercepted 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 re-execute part of their instructions reinterpret the same instruction 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. The first commercial programmer was probably Grace Hopper (1906-92), an American. To facilitate computer use in scientific applications, IBM then developed a language that would simplify work involving complicated mathematical formulas. Begun in 1954 and completed in 1957, FORTRAN (FORmula TRANslator) was the first comprehensive high-level programming language that was widely used. COBOL (COmmon Business Oriented Language), a commercial and business programming language, concentrated on data organization and file handling and is widely used today in business. BASIC (Beginner's All-purpose Symbolic Instruction Code) was developed for use by nonprofessional computer users. The language came into almost universal use 37 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. Although hundreds of different computer languages and variants exist, several others deserve mention. PASCAL, 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 and PROLOG are widely used in artificial intelligence.

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