Lvalue Required As Left Operand Of Assignment Incremental Innovation

std::cout<<"hello world!"<<std::endl;

Let's parse it:

\u2022

std::cout is the qualified name of the standard output stream object, cout. This object is

automatically created whenever you #include <iostream>.

\u2022

The overloaded insertion operator<< comes next. It takes an argument and passes it on tocout.

In this case, the argument is a literal string that we want to print on the screen.

\u2022

The second argument,std::endl, is amanipulator that appends the newline character after the

string and forces buffer flushing.

As trivial as this program seems, it exposes some of the most important features of C++. For starters, C++ is
an object-oriented language. Therefore, it uses objects rather than functions to perform I/O. Secondly, the
standard libraries of C++, including<iostream>, are declared in the namespacestd (std stands for

standard. An exhaustive discussion about namespaces is available in the "Namespaces" section.). Thus,

instead of declaring standard functions, classes, and objects globally, C++ declares them in a dedicated
namespace\u2014thereby reducing the chances of clashing with user code and third-party libraries that happen
to use the same names.

Overloading

The operator<< is particularly interesting. It behaves as a function that takes an argument, yet it looks like
the built-in left-shift operator. In reality, it's an overloaded operator. Operator overloading is another
fundamental concept of C++. An overloaded operator is a function whose name is an operator rather than a
string. You can override almost all the built-in operators of C++ (+, *, >, and so on) this way. Operator
overloading may sound revolutionary and even dangerous at first; after all, if programmers are free to
override the meaning of built-in operators, what's to stop them from defining operator+ as the subtraction
operator? Rest assured. C++ imposes certain restrictions on operator overloading. The combination of these
restrictions and good object-oriented practices guarantee that this feature makes code uniform and intuitive.

Consider the notion of a string. In C, assigning strings with the= operator is not allowed. By contrast, the
C++std::string class overloads this operator and enables you to perform direct assignments of
strings. For example:

std::string s;

s= "please fasten your seatbelt";

Without operator overloading, the snippet would look like this:

std::string s;

s.assign("please fasten your seatbelt");

When dealing with numeric libraries, the ability to overload operators (such as==,+,and-) for user-defined

types is particularly useful.

Overloading in C++ isn't limited to operators. You can also overload functions by giving two or morefunctions an identical name. The overloaded functions are distinguished by their parameter list. Forexample, a function that opens a file may have three different overloaded versions:

int file_open(int descriptor); // #1
int file_open(const char *pathname); // #2
int file_open(const string & pathname); // #3

The compiler determines which of the three overloaded versions is to be called by examining the function's

argument. For example:

std::string file="modem.log";

file_open(file); // call file_open() #3

Перед камерой появился агент Смит. - Мы выстрелили в него новым «Джей-23», это нервно-паралитическое вещество продолжительного действия. Конечно, это чертовски болезненно, но нам нужно было его остановить. - Не волнуйтесь, мадам, - заверил второй агент.  - С ним все будет в порядке.

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