>>> Using the standard input and output library, we will be able to interact with the user by printing messages on the screen and getting the user's input from the keyboard.
>>> The standard C++ library include the header file iostream, where the standard input and output stream objects are declared.
Standard Output ( Cout )
>>> By default, the standard output of a program is the screen and the C++ stream object defined to access it is cout.
>>> Cout is actually an object, predefined in C++ to correspond to the standard output stream. A stream is nothing but the flow of data.
>>> Cout is used in conjunction with the insertion operator, which is written as << ( two "less than" signs). It directs the contents of the variable on its right to the object on its left.
cout <<"hello"; // prints hello on screen
cout << 300; // prints number 300 on screen
cout << x; // prints the content of x on screen
>>> The << operator inserts the data that follows it into the stream preceding it.
>>> In the examples above it inserted the constant string Hello, the numerical constant 300 and variable x in the standard output stream cout.
>>> Notice that the sentence in the first instruction is enclosed between double quotes (") because it is a constant string of characters.
>>> Whenever we want to use constant strings of characters we must enclose them between double quotes (") s that they can be clearly distinguished from variable names. For example, these two sentence have very different results:
cout << "Hello"; // Prints Hello
cout << Hello; // Prints the content of Hello variable.
>>> The insertion operator ( << ) may be used more than once in a single statement:
cout << "Hello, "<<" I am " << " a C++ statement";
>>> This last statement would print the message Hello, I am a C++ statement on the screen. The utility of repeating the insertion operator (<<) is demonstrated when we want to print out a combination of variables and constants or more than one variable:
cout << " Hello, I am " << age << " years old and my zip code is " << zip code;
>>> If we assume the age variable to contain the value 24 and the zip code variable to contain 90064 the output of the previous statement would be:
Hello, I am 24 years old and my zip code is 90064
>>> It is important to notice that cout does not add a line break after its output unless we explicitly indicate it therefore, the following statements:
cout << "This is a sentence.";
cout << "This is another sentence.;
>>> Will be shown on the screen one following the other without any line break between them:
>>> Even though we had written them in two different insertions into cout. In order to perform a line break on the output we must explicitly insert a new line character into cout.
>>> In C++ new line character can be specified as \n (backslash,n);
cout << "First sentence. \";
cout << "Second sentence. \nThird sentence.";
>>> Additionally, to add a new line, you may also use the endl manipulator.
>>> For Example:
cout << "First sentence." << endl;
cout << "Second sentence." << endl;
>>> The endl manipulator products a newline character, exactly as the insertion of '\n' does, but it also has and additional behaviour when it is used with buffered streams: the buffer is flushed.