Computer education

PROGRAMMING LANGUAGES
Machine Language
Assembly Language
High-Level Languages
FLOW-MATIC
FORTRAN
BASIC

HOW COMPUTERS WORK
Operating System
Computer Memory
Bus
Input Devices
Central Processing Unit
Output Devices

HOW A CPU WORKS
INTRODUCTION
Function
Branching Instructions
Clock Pulses
Fixed-Point and Floating-Point Numbers

HISTORY
Early Computers
Transistor
The Integrated Circuit

High-Level Languages


High-level languages were developed because of the difficulty of programming using assembly languages. High-level languages are easier to use than machine and assembly languages because their commands are closer to natural human language. In addition, these languages are not CPU-specific. Instead, they contain general commands that work on different CPUs. For example, a programmer writing in the high-level C++ programming language who wants to display a greeting need include only the following command:

cout << ‘Hello, Auuuu User!’ << endl;

This command directs the computer’s CPU to display the greeting, and it will work no matter what type of CPU the computer uses. When this statement is executed, the text that appears between the quotes will be displayed. Although the “cout” and “endl” parts of the above statement appear cryptic, programmers quickly become accustomed to their meanings. For example, “cout” sends the greeting message to the “standard output” (usually the computer user’s screen) and “endl” is how to tell the computer (when using the C++ language) to go to a new line after it outputs the message. Like assembly-language instructions, high-level languages also must be translated. This is the task of a special program called a compiler. A compiler turns a high-level program into a CPU-specific machine language. For example, a programmer may write a program in a high-level language such as C++ or Java and then prepare it for different machines, such as a Sun Microsystems work station or a personal computer (PC), using compilers designed for those machines. This simplifies the programmer’s task and makes the software more portable to different users and machines.

OTHER HIGH-LEVEL LANGUAGES

Other high-level languages in use today include C, C++, Ada, Pascal, LISP, Prolog, COBOL, Visual Basic, and Java. Some languages, such as the “markup languages” known as HTML, XML, and their variants, are intended to display data, graphics, and media selections, especially for users of the World Wide Web. Markup languages are often not considered programming languages, but they have become increasingly sophisticated.

Object-Oriented Programming Languages

Object-oriented programming (OOP) languages, such as C++ and Java, are based on traditional high-level languages, but they enable a programmer to think in terms of collections of cooperating objects instead of lists of commands. Objects, such as a circle, have properties such as the radius of the circle and the command that draws it on the computer screen. Classes of objects can inherit features from other classes of objects. For example, a class defining squares can inherit features such as right angles from a class defining rectangles. This set of programming classes simplifies the programmer’s task, resulting in more “reusable” computer code. Reusable code allows a programmer to use code that has already been designed, written, and tested. This makes the programmer’s task easier, and it results in more reliable and efficient programs.

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