Imperative programming
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Imperative programming is a programming paradigm that describes computation as statements that change program state. Imperative programs are a sequence of commands for the computer to perform. Procedural programming is a common method of executing imperative programming, and the terms are often used as synonyms.
Imperative programming languages stand in contrast to other types of languages, such as functional and logical programming languages. Functional programming languages, such as Haskell, are not a sequence of statements and have no global state as imperative languages do. Logical programming languages, like Prolog, are often thought of as defining "what" is to be computed, rather than "how" the computation is to take place, as an imperative programming language does.
[edit] Overview
The hardware implementation of almost all computers is imperative; 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 general, 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 (such 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 block 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 the block. Unconditional branching statements allow the execution sequence to be transferred to some other part of the program. These include the jump, called "goto" in many languages, and the subprogram, or procedure, call.
[edit] References
- Pratt, Terrence W. and Marvin V. Zelkowitz. Programming Languages: Design and Implementation, 3rd ed. Englewood Cliffs, N.J.: Prentice Hall, 1996.
- Sebesta, Robert W. Concepts of Programming Languages, 3rd ed. Reading, Mass.: Addison-Wesley Publishing Company, 1996.
