Procedural language is a type of computer programming language that specifies a series of well-structured steps and procedures within its programming context to compose a program. It contains a systematic order of statements, functions and commands to complete a computational task or program
Procedural programming is a programming paradigm, derived from structured programming, based upon the concept of the procedure call. Procedures, also known as routines, subroutines, or functions (not to be confused with mathematical functions, but similar to those used in functional programming), simply contain a series of computational steps to be carried out. Any given procedure might be called at any point during a program’s execution, including by other procedures or itself.
Computer processors provide hardware support for procedural programming through a stack register and instructions for calling procedures and returning from them.
Procedures and modularity
Main article: Modular programming
Modularity is generally desirable, especially in large, complicated programs. Inputs are usually specified syntactically in the form of arguments and the outputs delivered as return values.
Scoping is another technique that helps keep procedures modular. It prevents the procedure from accessing the variables of other procedures (and vice versa), including previous instances of itself, without explicit authorization.
Less modular procedures, often used in small or quickly written programs, tend to interact with a large number of variables in the execution environment, which other procedures might also modify.
Because of the ability to specify a simple interface, to be self-contained, and to be reused, procedures are a convenient vehicle for making pieces of code written by different people or different groups, including through programming libraries.
Comparison with imperative programmingEdit
Procedural programming languages are also imperative languages, because they make explicit references to the state of the execution environment. This could be anything from variables (which may correspond to processor registers) to something like the position of the “turtle” in the Logo programming language.
Often, the terms “procedural programming” and “imperative programming” are used synonymously. However, procedural programming relies heavily on blocks and scope, whereas imperative programming as a whole may or may not have such features. As such, procedural languages generally use reserved words that act on blocks, such as if, while, and for, to implement control flow, whereas non-structured imperative languages use goto statements and branch tables for the same purpose.
Comparison with object-oriented programmingEdit
The focus of procedural programming is to break down a programming task into a collection of variables, data structures, and subroutines, whereas in object-oriented programming it is to break down a programming task into objects that expose behavior (methods) and data (members or attributes) using interfaces. The most important distinction is that while procedural programming uses procedures to operate on data structures, object-oriented programming bundles the two together, so an “object”, which is an instance of a class, operates on its “own” data structure.[2]
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http://searchsoa.techtarget.com/definition/object-oriented-programming
Object-oriented programming (OOP) is a programming language model organized around objects rather than “actions” and data rather than logic. Historically, a program has been viewed as a logical procedure that takes input data, processes it, and produces output data.
The programming challenge was seen as how to write the logic, not how to define the data. Object-oriented programming takes the view that what we really care about are the objects we want to manipulate rather than the logic required to manipulate them.
The first step in OOP is to identify all the objects the programmer wants to manipulate and how they relate to each other, an exercise often known as data modeling. Once an object has been identified, it is generalized as a class of objects which defines the kind of data it contains and any logic sequences that can manipulate it. Each distinct logic sequence is known as a method. Objects communicate with well-defined interfaces called messages.
The concepts and rules used in object-oriented programming provide these important benefits:
The concept of a data class makes it possible to define subclasses of data objects that share some or all of the main class characteristics. Called inheritance, this property of OOP forces a more thorough data analysis, reduces development time, and ensures more accurate coding.
Since a class defines only the data it needs to be concerned with, when an instance of that class (an object) is run, the code will not be able to accidentally access other program data. This characteristic of data hiding provides greater system security and avoids unintended data corruption.
The definition of a class is reuseable not only by the program for which it is initially created but also by other object-oriented programs (and, for this reason, can be more easily distributed for use in networks).
The concept of data classes allows a programmer to create any new data type that is not already defined in the language itself.
Simula was the first object-oriented programming language. Java, Python, C++, Visual Basic .NET and Ruby are the most popular OOP languages today. The Java programming language is designed especially for use in distributed applications on corporate networks and the Internet. Ruby is used in many Web applications.
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Object-oriented programming (OOP) is a programming paradigm based on the concept of “objects”, which may contain data, in the form of fields, often known as attributes; and code, in the form of procedures, often known as methods. A feature of objects is that an object’s procedures can access and often modify the data fields of the object with which they are associated (objects have a notion of “this” or “self”). In OOP, computer programs are designed by making them out of objects that interact with one another.[1][2] There is significant diversity of OOP languages, but the most popular ones are class-based, meaning that objects are instances of classes, which typically also determine their type.
Many of the most widely used programming languages are multi-paradigm programming languages that support object-oriented programming to a greater or lesser degree, typically in combination with imperative, procedural programming. Significant object-oriented languages include Java, C++, C#, Python, PHP, Ruby, Perl, Delphi, Objective-C, Swift, Common Lisp, and Smalltalk.
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In computer science, imperative programming is a programming paradigm that uses statements that change a program’s state. In much the same way that the imperative mood in natural languages expresses commands, an imperative program consists of commands for the computer to perform. Imperative programming focuses on describing how a program operates.
The term is often used in contrast to declarative programming, which focuses on what the program should accomplish without specifying how the program should achieve the result.
Imperative and procedural programming
Procedural programming is a type of imperative programming in which the program is built from one or more procedures (also termed subroutines or functions). The terms are often used as synonyms, but the use of procedures has a dramatic effect on how imperative programs appear and how they are constructed. Heavily-procedural programming, in which state changes are localized to procedures or restricted to explicit arguments and returns from procedures, is a form of structured programming. From the 1960s onwards, structured programming and modular programming in general have been promoted as techniques to improve the maintainability and overall quality of imperative programs. The concepts behind object-oriented programming attempt to extend this approach.[1]
Procedural programming could be considered a step towards declarative programming. A programmer can often tell, simply by looking at the names, arguments, and return types of procedures (and related comments), what a particular procedure is supposed to do, without necessarily looking at the details of how it achieves its result. At the same time, a complete program is still imperative since it fixes the statements to be executed and their order of execution to a large extent.
Rationale and foundations of imperative programming
The hardware implementation of almost all computers is imperative.[note 1] Nearly all computer hardware is designed to execute machine code, which is native to the computer, written in the imperative style. From this low-level perspective, the program state is defined by the contents of memory, and the statements are instructions in the native machine language of the computer. Higher-level imperative languages use variables and more complex statements, but still follow the same paradigm. Recipes and process checklists, while not computer programs, are also familiar concepts that are similar in style to imperative programming; each step is an instruction, and the physical world holds the state. Since the basic ideas of imperative programming are both conceptually familiar and directly embodied in the hardware, most computer languages are in the imperative style.
Assignment statements, in imperative paradigm, perform an operation on information located in memory and store the results in memory for later use. High-level imperative languages, in addition, permit the evaluation of complex expressions, which may consist of a combination of arithmetic operations and function evaluations, and the assignment of the resulting value to memory. Looping statements (as in while loops, do while loops, and for loops) allow a sequence of statements to be executed multiple times. Loops can either execute the statements they contain a predefined number of times, or they can execute them repeatedly until some condition changes. Conditional branching statements allow a sequence of statements to be executed only if some condition is met. Otherwise, the statements are skipped and the execution sequence continues from the statement following them. Unconditional branching statements allow an execution sequence to be transferred to another part of a program. These include the jump (called goto in many languages), switch, and the subprogram, subroutine, or procedure call (which usually returns to the next statement after the call).
Early in the development of high-level programming languages, the introduction of the block enabled the construction of programs in which a group of statements and declarations could be treated as if they were one statement. This, alongside the introduction of subroutines, enabled complex structures to be expressed by hierarchical decomposition into simpler procedural structures.
Many imperative programming languages (such as Fortran, BASIC, and C) are abstractions of assembly language.[2]
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In computer programming, a statement is the smallest standalone element of an imperative programming language that expresses some action to be carried out. It is an instruction written in a high-level language that commands the computer to perform a specified action.[1] A program written in such a language is formed by a sequence of one or more statements. A statement may have internal components (e.g., expressions).
Many languages (e.g. C) make a distinction between statements and definitions, with a statement only containing executable code and a definition instantiating an identifier, while an expression evaluates to a value only. A distinction can also be made between simple and compound statements; the latter may contain statements as components.
use(f)
Syntax
The appearance of statements shapes the look of programs. Programming languages are characterized by the type of statements they use (e.g. the curly brace language family). Many statements are introduced by identifiers like if, while or repeat. Often statement keywords are reserved such that they cannot be used as names of variables or functions. Imperative languages typically use special syntax for each statement, which looks quite different from function calls. Common methods to describe the syntax of statements are Backus–Naur form and syntax diagrams.
SemanticsEdit
Semantically many statements differ from subroutine calls by their handling of parameters. Usually an actual subroutine parameter is evaluated once before the subroutine is called. This contrasts to many statement parameters that can be evaluated several times (e.g. the condition of a while loop) or not at all (e.g. the loop body of a while loop). Technically such statement parameters are call-by-name parameters. Call-by-name parameters are evaluated when needed (see also lazy evaluation). When call-by-name parameters are available a statement like behaviour can be implemented with subroutines (see Lisp). For languages without call-by-name parameters the semantic description of a loop or conditional is usually beyond the capabilities of the language. Therefore standard documents often refer to semantic descriptions in natural language.
Expressions
In most languages, statements contrast with expressions in that statements do not return results and are executed solely for their side effects, while expressions always return a result and often do not have side effects at all. Among imperative programming languages, Algol 68 is one of the few in which a statement can return a result. In languages that mix imperative and functional styles, such as the Lisp family, the distinction between expressions and statements is not made: even expressions executed in sequential contexts solely for their side effects and whose return values are not used are considered ‘expressions’. In purely functional programming, there are no statements; everything is an expression.
This distinction is frequently observed in wording: a statement is executed, while an expression is evaluated. This is found in the exec and eval functions found in some languages: in Python both are found, with exec applied to statements and eval applied to expressions.
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In computer science, functional programming is a programming paradigm that treats computation as the evaluation of mathematical functions and avoids state and mutable data. It emphasizes the application of functions, in contrast with the procedural programming style that emphasizes changes in state.
“Functional programming is like describing your problem to a mathematician. Imperative programming is like giving instructions to an idiot.”
The point is that procedural programming happens stepwise in a pre-determined order, whereas functional programs are not executed stepwise; rather, values are computed when they are needed. However, the lack of a generally agreed upon definition of programming terminology makes such generalisations next to useless.
Basically the two styles, are like Yin and Yang. One is organized, while the other chaotic. There are situations when Functional programming is the obvious choice, and other situations were Procedural programming is the better choice.
Procedural:
The output of a routine does not always have a direct correlation with the input.
Everything is done in a specific order.
Execution of a routine may have side effects.
Tends to emphasize implementing solutions in a linear fashion.
Functional:
Often recursive.
Always returns the same output for a given input.
Order of evaluation is usually undefined.
Must be stateless. i.e. No operation can have side effects.
Good fit for parallel execution
Tends to emphasize a divide and conquer approach.
May have the feature of Lazy Evaluation
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In computer science, functional programming is a programming paradigm—a style of building the structure and elements of computer programs—that treats computation as the evaluation of mathematical functions and avoids changing-state and mutable data. It is a declarative programming paradigm, which means programming is done with expressions[1] or declarations[2] instead of statements. In functional code, the output value of a function depends only on the arguments that are input to the function, so calling a function f twice with the same value for an argument x will produce the same result f(x) each time. Eliminating side effects, i.e. changes in state that do not depend on the function inputs, can make it much easier to understand and predict the behavior of a program, which is one of the key motivations for the development of functional programming.
In contrast, imperative programming changes state with commands in the source language, the most simple example being assignment. Imperative programming does have functions—not in the mathematical sense—but in the sense of subroutines. They can have side effects that may change the value of program state. Functions without return values therefore make sense. Because of this, they lack referential transparency, i.e. the same language expression can result in different values at different times depending on the state of the executing program.[3]
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In computer science, declarative programming is a programming paradigm—a style of building the structure and elements of computer programs—that expresses the logic of a computation without describing its control flow.[1]
Many languages that apply this style attempt to minimize or eliminate side effects by describing what the program must accomplish in terms of the problem domain, rather than describe how to accomplish it as a sequence of the programming language primitives[2] (the how being left up to the language’s implementation). This is in contrast with imperative programming, which implements algorithms in explicit steps.
Declarative programming often considers programs as theories of a formal logic, and computations as deductions in that logic space. Declarative programming may greatly simplify writing parallel programs.[3]
Common declarative languages include those of database query languages (e.g., SQL, XQuery), regular expressions, logic programming, functional programming, and configuration management systems.
Definition
Declarative programming is often defined as any style of programming that is not imperative. A number of other common definitions exist that attempt to give the term a definition other than simply contrasting it with imperative programming. For example:
A program that describes what computation should be performed and not how to compute it
Any programming language that lacks side effects (or more specifically, is referentially transparent)
A language with a clear correspondence to mathematical logic.[4]
These definitions overlap substantially.
Declarative programming contrasts with imperative and procedural programming. Declarative programming is a non-imperative style of programming in which programs describe their desired results without explicitly listing commands or steps that must be performed. Functional and logical programming languages are characterized by a declarative programming style. In logical programming languages, programs consist of logical statements, and the program executes by searching for proofs of the statements.
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The state of something is the set of values that its attributes have in any given moment.
In computer science and automata theory, the state of a digital logic circuit or computer program is a technical term for all the stored information, at a given instant in time, to which the circuit or program has access.[1] The output of a digital circuit or computer program at any time is completely determined by its current inputs and its state.
Digital logic circuit state
Digital logic circuits can be divided into two types: combinational logic, whose output signals are dependent only on its present input signals, and sequential logic, whose outputs are a function of both the current inputs and the past history of inputs.[2] In sequential logic, information from past inputs is stored in electronic memory elements, such as flip-flops and latches. The stored contents of these memory elements, at a given point in time, is collectively referred to as the circuit’s state and contains all the information about the past to which the circuit has access.[3]
For example, the state of a microprocessor is the contents of all the memory elements in it: the accumulators, storage registers, data caches, and flags. When computers such as laptops go into a hibernation mode to save energy by shutting down the processor, the state of the processor is stored on the computer’s hard disk, so it can be restored when the computer comes out of hibernation, and the processor can take up operations where it left off.
Since each binary memory element, such as a flip-flop, has only two possible states, “one” or “zero”, and there is a finite number of memory elements, a digital circuit has only a certain finite number of possible states. If N is the number of binary memory elements in the circuit, the maximum number of states a circuit can have is 2N.
Program state
Similarly, a computer program stores data in variables, which represent storage locations in the computer’s memory. The contents of these memory locations, at any given point in the program’s execution, is called the program’s state.[4][5][6]
Imperative programming is a programming paradigm (way of designing a programming language) that describes computation in terms of the program state and statements that change the program state. In contrast, in declarative programming languages the program describes the desired results, and doesn’t specify changes to the state directly.
A more specialized definition of state is used in some computer programs that operate serially (sequentially) on streams of data, such as parsers, firewalls, communication protocols and encryption programs. Serial programs operate on the incoming data characters or packets sequentially, one at a time. In some of these programs, information about previous data characters or packets received is stored in variables and used to affect the processing of the current character or packet. This is called a “stateful protocol” and the data carried over from the previous processing cycle is called the “state”. In others, the program has no information about the previous data stream and starts “fresh” with each data input; this is called a “stateless protocol”.
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Programming languages that include dynamic type checking but not static type checking are often called “dynamically typed programming languages”.
Many programming languages require computation to be specified in an imperative form (i.e., as a sequence of operations to perform), while other languages use other forms of program specification such as the declarative form (i.e. the desired result is specified, not how to achieve it).
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Goto (goto, GOTO, GO TO or other case combinations, depending on the programming language) is a statement found in many computer programming languages. It performs a one-way transfer of control to another line of code; in contrast a function call normally returns control. The jumped-to locations are usually identified using labels, though some languages use line numbers. At the machine code level, a goto is a form of branch or jump statement. Many languages support the goto statement, and many do not (see language support).
The structured program theorem proved that the goto statement is not necessary to write programs; some combination of the three programming constructs of sequence, selection/choice, and repetition/iteration are sufficient for any computation that can be performed by a Turing machine, with the caveat that code duplication and additional variables may need to be introduced.[1]
In the past there was considerable debate in academia and industry on the merits of the use of goto statements. Use of goto was formerly common, but since the advent of structured programming in the 1960s and 1970s its use has declined significantly. The primary criticism is that code that uses goto statements is harder to understand than alternative constructions. Goto remains in use in certain common usage patterns, but alternatives are generally used if available. Debates over its (more limited) uses continue in academia and software industry circles.
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In computer programming, a subroutine is a sequence of program instructions that perform a specific task, packaged as a unit. This unit can then be used in programs wherever that particular task should be performed. Subprograms may be defined within programs, or separately in libraries that can be used by multiple programs. In different programming languages, a subroutine may be called a procedure, a function, a routine, a method, or a subprogram. The generic term callable unit is sometimes used.[1]
The name subprogram suggests a subroutine behaves in much the same way as a computer program that is used as one step in a larger program or another subprogram. A subroutine is often coded so that it can be started (called) several times and from several places during one execution of the program, including from other subroutines, and then branch back (return) to the next instruction after the call, once the subroutine’s task is done. Maurice Wilkes, David Wheeler, and Stanley Gill are credited with the invention of this concept, which they termed a closed subroutine,[2][3] contrasted with an open subroutine or macro.[4]
Subroutines are a powerful programming tool,[5] and the syntax of many programming languages includes support for writing and using them. Judicious use of subroutines (for example, through the structured programming approach) will often substantially reduce the cost of developing and maintaining a large program, while increasing its quality and reliability.[6] Subroutines, often collected into libraries, are an important mechanism for sharing and trading software. The discipline of object-oriented programming is based on objects and methods (which are subroutines attached to these objects or object classes).
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The following are considered[by whom?] the main programming paradigms. There is inevitably some overlap in these paradigms but the main features or identifiable differences are summarized in the following table:
Imperative programming – defines computation as statements that change a program state
Procedural programming, structured programming – specifies the steps the program must take to reach the desired state.
Declarative programming – defines computation logic without defining its control flow.
Functional programming – treats computation as the evaluation of mathematical functions and avoids state and mutable data
Object-oriented programming (OOP) – organizes programs as objects: data structures consisting of datafields and methods together with their interactions.
Event-driven programming – the flow of the program is determined by events, such as sensor outputs or user actions (mouse clicks, key presses) or messages from other programs or threads.
Automata-based programming – a program, or part, is treated as a model of a finite state machine or any other formal automaton.
None of the main programming paradigms have a precise, globally unanimous definition, let alone an official international standard. Nor is there any agreement on which paradigm constitutes the best approach to developing software. The subroutines that actually implement OOP methods might be ultimately coded in an imperative, functional or procedural style that might, or might not, directly alter state on behalf of the invoking program.
Expressions
In most languages, statements contrast with expressions in that statements do not return results and are executed solely for their side effects, while expressions always return a result and often do not have side effects at all. Among imperative programming languages, Algol 68 is one of the few in which a statement can return a result. In languages that mix imperative and functional styles, such as the Lisp family, the distinction between expressions and statements is not made: even expressions executed in sequential contexts solely for their side effects and whose return values are not used are considered ‘expressions’. In purely functional programming, there are no statements; everything is an expression.
This distinction is frequently observed in wording: a statement is executed, while an expression is evaluated. This is found in the exec and eval functions found in some languages: in Python both are found, with exec applied to statements and eval applied to expressions.