The terms low level and high level are often used to describe these layers of complexity in computers. The low level is buried in the computer's microchips and microcircuits.
C and C++ books-page5
GNU C Programming Tutorial
The terms low level and high level are often used to describe these layers of complexity in computers. The low level is buried in the computer's microchips and microcircuits. The low level is the level at which the computer seems most primitive and mechanical, whereas the high level describes the computer in less detail, and makes it easier to use.
You can see high levels and low levels in the workings of a car. In a car, the nuts, bolts, and pistons of the low level can be grouped together conceptually to form the higher-level engine. Without knowing anything about the nuts and bolts, you can treat the engine as a black box: a simple unit that behaves in predictable ways. At an even higher level (the one most people use when driving), you can see a car as a group of these black boxes, including the engine, the steering, the brakes, and so on. At a high level, a computer also becomes a group of black boxes.
Introduction to The Objective-C Programming Language
An object-oriented approach to application development makes programs more intuitive to design, faster to develop, more amenable to modification, and easier to understand. Most object-oriented development environments consist of at least three parts:
* A library of objects * A set of development tools * An object-oriented programming language and support library , This document is about the third component of the development
environment-the programming language and its runtime environment. It fully describes the Objective-C language, and provides a foundation for learning about the Mac OS X Objective-C application development
The C Shell
Tutorial A shell is a program which provides a user interface. With a shell, users can type in commands and run programs on a Unix system. Basically, the main function a shell performs is to read in from the terminal what one types, run the commands, and show the output of the commands.
The C shell has three separate files which are used for customizing its environment. These three files are .cshrc, .login, and .logout. Because these files begin with a period (.) they do not usually appear when one types the ls command. In order to see all files beginning with periods, the -a option is used with the ls command.
The Object- C runtime Reference This document describes the Mac OS X Objective-C runtime library support functions and data structures. The functions are implemented in the shared library found at /usr/lib/libobjc.A.dylib. This shared library provides support for the dynamic properties of the Objective-C language, and as such is linked to by all Objective-C applications.
This reference is useful primarily for developing bridge layers between Objective-C and other languages, or for low-level debugging. You typically do not need to use the Objective-C runtime library directly when programming in Objective-C.
The Mac OS X implementation of the Objective-C runtime library is unique to the Mac OS X platform. For other platforms, the GNU Compiler Collection provides a different implementation with a similar API. This document covers only the Mac OS X implementation.