Tuesday, December 29, 2015

Cout, Cin

   >>> 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.";

            output :
                               First sentence.
                               Second sentence.
                               Third sentence.

   >>> Additionally, to add a new line, you may also use the endl manipulator.

   >>> For Example:

                                  cout << "First sentence." << endl;
                                  cout << "Second sentence." << endl;

              output :
                               First sentence.
                               Second sentence.

   >>> 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.

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