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Magic Number (programming)
In computer programming, a magic number is any of the following: * A unique value with unexplained meaning or multiple occurrences which could (preferably) be replaced with a named constant * A constant numerical or text value used to identify a file format or protocol; for files, see List of file signatures * A distinctive unique value that is unlikely to be mistaken for other meanings (e.g., Globally Unique Identifiers) Unnamed numerical constants The term ''magic number'' or ''magic constant'' refers to the anti-pattern of using numbers directly in source code. This has been referred to as breaking one of the oldest rules of programming, dating back to the COBOL, FORTRAN and PL/1 manuals of the 1960s. The use of unnamed magic numbers in code obscures the developers' intent in choosing that number, increases opportunities for subtle errors (e.g. is every digit correct in 3.14159265358979323846 and is this equal to 3.14159?) and makes it more difficult for the program to be ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computer Programming
Computer programming is the process of performing a particular computation (or more generally, accomplishing a specific computing result), usually by designing and building an executable computer program. Programming involves tasks such as analysis, generating algorithms, Profiling (computer programming), profiling algorithms' accuracy and resource consumption, and the implementation of algorithms (usually in a chosen programming language, commonly referred to as coding). The source code of a program is written in one or more languages that are intelligible to programmers, rather than machine code, which is directly executed by the central processing unit. The purpose of programming is to find a sequence of instructions that will automate the performance of a task (which can be as complex as an operating system) on a computer, often for solving a given problem. Proficient programming thus usually requires expertise in several different subjects, including knowledge of the Domain ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Code Reuse
In software development (and computer programming in general), code reuse, also called software reuse, is the use of existing software, or software knowledge, to build new software, following the reusability principles. Code reuse may be achieved by different ways depending on a complexity of a programming language chosen and range from a lower-level approaches like code copy-pasting (e.g. via snippets), simple functions ( procedures or subroutines) or a bunch of objects or functions organized into modules (e.g. libraries) or custom namespaces, and packages, frameworks or software suites in higher-levels. Code reuse implies dependencies which can make code maintanability harder. At least one study found that code reuse reduces technical debt. Overview Ad hoc code reuse has been practiced from the earliest days of programming. Programmers have always reused sections of code, templates, functions, and procedures. Software reuse as a recognized area of study in softwa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Digital Equipment Corporation
Digital Equipment Corporation (DEC ), using the trademark Digital, was a major American company in the computer industry from the 1960s to the 1990s. The company was co-founded by Ken Olsen and Harlan Anderson in 1957. Olsen was president until forced to resign in 1992, after the company had gone into precipitous decline. The company produced many different product lines over its history. It is best known for the work in the minicomputer market starting in the mid-1960s. The company produced a series of machines known as the PDP line, with the PDP-8 and PDP-11 being among the most successful minis in history. Their success was only surpassed by another DEC product, the late-1970s VAX "supermini" systems that were designed to replace the PDP-11. Although a number of competitors had successfully competed with Digital through the 1970s, the VAX cemented the company's place as a leading vendor in the computer space. As microcomputers improved in the late 1980s, especially ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Unix
Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and others. Initially intended for use inside the Bell System, AT&T licensed Unix to outside parties in the late 1970s, leading to a variety of both academic and commercial Unix variants from vendors including University of California, Berkeley ( BSD), Microsoft (Xenix), Sun Microsystems ( SunOS/ Solaris), HP/ HPE ( HP-UX), and IBM (AIX). In the early 1990s, AT&T sold its rights in Unix to Novell, which then sold the UNIX trademark to The Open Group, an industry consortium founded in 1996. The Open Group allows the use of the mark for certified operating systems that comply with the Single UNIX Specification (SUS). Unix systems are characterized by a modular design that is sometimes called the "Unix philosophy". According to th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Version 7 Unix
Seventh Edition Unix, also called Version 7 Unix, Version 7 or just V7, was an important early release of the Unix operating system. V7, released in 1979, was the last Bell Laboratories release to see widespread distribution before the commercialization of Unix by AT&T Corporation in the early 1980s. V7 was originally developed for Digital Equipment Corporation's PDP-11 minicomputers and was later ported to other platforms. Overview Unix versions from Bell Labs were designated by the edition of the user's manual with which they were accompanied. Released in 1979, the Seventh Edition was preceded by Sixth Edition, which was the first version licensed to commercial users. Development of the Research Unix line continued with the Eighth Edition, which incorporated development from 4.1BSD, through the Tenth Edition, after which the Bell Labs researchers concentrated on developing Plan 9. V7 was the first readily portable version of Unix. As this was the era of minicomputers, wit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Null Pointer
In computing, a null pointer or null reference is a value saved for indicating that the pointer or reference does not refer to a valid object. Programs routinely use null pointers to represent conditions such as the end of a list of unknown length or the failure to perform some action; this use of null pointers can be compared to nullable types and to the ''Nothing'' value in an option type. A null pointer should not be confused with an uninitialized pointer: a null pointer is guaranteed to compare unequal to any pointer that points to a valid object. However, depending on the language and implementation, an uninitialized pointer may not have any such guarantee. It might compare equal to other, valid pointers; or it might compare equal to null pointers. It might do both at different times; or the comparison might be undefined behaviour. C In C, two null pointers of any type are guaranteed to compare equal. The preprocessor macro NULL is defined as an implementation-defin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Primitive Type
In computer science, primitive data types are a set of basic data types from which all other data types are constructed. Specifically it often refers to the limited set of data representations in use by a particular processor, which all compiled programs must use. Most processors support a similar set of primitive data types, although the specific representations vary. More generally, "primitive data types" may refer to the standard data types built into a programming language. Data types which are not primitive are referred to as ''derived'' or ''composite''. Primitive types are almost always value types, but composite types may also be value types. Common primitive data types The Java virtual machine's set of primitive data types is: * Integer types with a variety of ranges and precisions (byte, short, int, long, char) * Floating-point number with single or double precisions; (float, double) * Boolean, logical values true and false. (boolean) * A value referring to an execu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
C (programming Language)
C (''pronounced like the letter c'') is a general-purpose computer programming language. It was created in the 1970s by Dennis Ritchie, and remains very widely used and influential. By design, C's features cleanly reflect the capabilities of the targeted CPUs. It has found lasting use in operating systems, device drivers, protocol stacks, though decreasingly for application software. C is commonly used on computer architectures that range from the largest supercomputers to the smallest microcontrollers and embedded systems. A successor to the programming language B, C was originally developed at Bell Labs by Ritchie between 1972 and 1973 to construct utilities running on Unix. It was applied to re-implementing the kernel of the Unix operating system. During the 1980s, C gradually gained popularity. It has become one of the most widely used programming languages, with C compilers available for practically all modern computer architectures and operating systems. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Boolean Data Type
In computer science, the Boolean (sometimes shortened to Bool) is a data type that has one of two possible values (usually denoted ''true'' and ''false'') which is intended to represent the two truth values of logic and Boolean algebra. It is named after George Boole, who first defined an algebraic system of logic in the mid 19th century. The Boolean data type is primarily associated with conditional statements, which allow different actions by changing control flow depending on whether a programmer-specified Boolean ''condition'' evaluates to true or false. It is a special case of a more general ''logical data type—''logic does not always need to be Boolean (see probabilistic logic). Generalities In programming languages with a built-in Boolean data type, such as Pascal and Java, the comparison operators such as > and ≠ are usually defined to return a Boolean value. Conditional and iterative commands may be defined to test Boolean-valued expressions. Languages with no ex ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Per Mille
Per mille (from Latin , "in each thousand") is an expression that means parts per thousand. Other recognised spellings include per mil, per mill, permil, permill, or permille. The associated sign is written , which looks like a percent sign with an extra zero or o in the divisor. The term occurs so rarely in English that major dictionaries do not agree on the spelling and some major dictionaries such as ''Macmillan'' do not even contain an entry. The term is more common in other European languages where it is used to express fractions smaller than 1%. One common usage is blood alcohol content, which is usually expressed as a percentage in English-speaking countries. Per mille should not be confused with parts per million (ppm). Computer systems The code point for the glyph is included in the General Punctuation block of Unicode characters: .Unicode.General Punctuation. 2014. Accessed 5 Aug 2014. It may be typed using , , , or according to operating system. No ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quadratic Equation
In algebra, a quadratic equation () is any equation that can be rearranged in standard form as ax^2 + bx + c = 0\,, where represents an unknown value, and , , and represent known numbers, where . (If and then the equation is linear, not quadratic.) The numbers , , and are the '' coefficients'' of the equation and may be distinguished by respectively calling them, the ''quadratic coefficient'', the ''linear coefficient'' and the ''constant'' or ''free term''. The values of that satisfy the equation are called '' solutions'' of the equation, and ''roots'' or '' zeros'' of the expression on its left-hand side. A quadratic equation has at most two solutions. If there is only one solution, one says that it is a double root. If all the coefficients are real numbers, there are either two real solutions, or a single real double root, or two complex solutions that are complex conjugates of each other. A quadratic equation always has two roots, if complex roots are included; a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Discriminant
In mathematics, the discriminant of a polynomial is a quantity that depends on the coefficients and allows deducing some properties of the roots without computing them. More precisely, it is a polynomial function of the coefficients of the original polynomial. The discriminant is widely used in polynomial factoring, number theory, and algebraic geometry. The discriminant of the quadratic polynomial ax^2+bx+c is :b^2-4ac, the quantity which appears under the square root in the quadratic formula. If a\ne 0, this discriminant is zero if and only if the polynomial has a double root. In the case of real coefficients, it is positive if the polynomial has two distinct real roots, and negative if it has two distinct complex conjugate roots. Similarly, the discriminant of a cubic polynomial is zero if and only if the polynomial has a multiple root. In the case of a cubic with real coefficients, the discriminant is positive if the polynomial has three distinct real roots, and negat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
