programming

A program flow chart shows the sequence of operations needed to achieve a task, in this case reading customer accounts and calculating the amount due for each customer. After an account has been processed, the program loops back to process the next one.

The sequence of events when running an interpreter on a high-level language program. Instructions are translated one at a time, making the process a slow one; however, interpreted programs do not need to be compiled and may be executed immediately.

The relationship between the three main areas of a computer's central processing unit. The arithmetic and logic unit (ALU) does the arithmetic, using the registers to store intermediate results, supervised by the control unit. Input and output circuits connect the ALU to external memory, input, and output devices.

The process of compilation; a program written in a high-level language is translated into a program that can be run without the original source being present.

Writing instructions in a programming language for the control of a computer. Applications programming is for end-user programs, such as accounts programs or word-processing packages. Systems programming is for operating systems and the like, which are concerned more with the internal workings of the computer.

There are several programming styles. Procedural programming, in which programs are written as lists of instructions for the computer to obey in sequence, is by far the most popular. It is the ‘natural’ style, closely matching the computer's own sequential operation. Declarative programming, as used in the programming language PROLOG, does not describe how to solve a problem, but rather describes the logical structure of the problem. Running such a program is more like proving an assertion than following a procedure. Functional programming is a style based largely on the definition of functions. There are very few functional programming languages, HOPE and ML being the most widely used, though many more conventional languages (for example C) make extensive use of functions. Object-oriented programming, the most recently developed style, involves viewing a program as a collection of objects that behave in certain ways when they are passed certain ‘messages’. For example, an object might be defined to represent a table of figures, which will be displayed on screen when a ‘display’ message is received.