An object is a variable of a class type, as distinct from a variable of a native type. The behavior of an object is defined by the code that implements the class to which the object belongs. For example, a variable of type string is an object whose behavior is controlled by the definition of the string class.

Object code; see machine code. This term is unrelated to C++ objects.

An object code module is the result of compiling a source code module into object code. A number of object code modules are combined to form an executable program. This term is unrelated to C++ objects.

Object file; see object code module. This term is unrelated to C++ objects.

Object-oriented programming is an approach to solving programming problems by creating objects to represent the entities being handled by the program, rather than relying solely on native data types. This approach has the advantage that you can match the language to the needs of the problem you're trying to solve. For example, if you were writing a nurse's station program in C++, you would want to have objects that represented nurses, doctors, patients, various sorts of equipment, and so on. Each of these objects would display the behavior appropriate to the thing or person it was representing.

Off-by-one error; see fencepost error.

An ofstream (pronounced "o f stream") is a stream used for output to a file.

An op code is the part of a machine instruction that tells the CPU what kind of instruction this is and sometimes also specifies a register to be operated on.

An operating system is a program that deals with the actual hardware of your computer; it supplies the lowest level of the software infrastructure needed to run a program. By far the most common operating system for Intel CPUs, at present, is MS-DOS, followed by OS/2 and Windows NT.

The keyword operator is used to indicate that the following symbol is the name of a C++ operator that we are redefining, either globally or for a particular class. For example, to redefine =, we have to specify operator = as the name of the function we are writing, rather than just =, so that the compiler does not object to seeing an operator when it expects an identifier.

An ostream is a stream used for output. For example, cout is a predefined ostream that displays characters on the screen.

Output is the process of sending data from the computer to the outside world. The most commonly used source of output for most programs is the screen.

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