Procedural programming

Procedural programming is a programming paradigm, derived from structured programming, based on the concept of the procedure call. Procedures, also known as routines, subroutines, or functions, 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. The first major procedural programming languages first appeared circa 1960, including Fortran, ALGOL, COBOL and BASIC. Pascal and C were published closer to the 1970s. Procedural programming is a programming paradigm, derived from structured programming, based on the concept of the procedure call. Procedures, also known as routines, subroutines, or functions, 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. The first major procedural programming languages first appeared circa 1960, including Fortran, ALGOL, COBOL and BASIC. Pascal and C were published closer to the 1970s. Computer processors provide hardware support for procedural programming through a stack register and instructions for calling procedures and returning from them. Hardware support for other types of programming is possible, but no attempt was commercially successful (for example Lisp machines or Java processors). 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. 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. 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.