Object Oriented programming language introduction (Basics)

      Basic Input

                                    and Output:

  1. C++ uses a convenient abstraction called streams to perform input and output operations in sequential media such as the screen, the keyboard or a file. A stream is an entity where a program can either insert or extract characters to/from.

  2. There is no need to know details about the media associated to the stream or any of its internal specifications. 

  3. All we need to know is that streams are a source/destination of characters, and that these characters are provided/accepted sequentially (i.e., one after another).

The standard library defines a handful of stream objects that can be used to access what are considered the standard sources and destinations of characters by the environment where the program runs:

stream description:

======================

cin   | standard input stream

===============================

cout  | standard output stream

cerr   | standard error (output) stream

clog  |      standard logging (output) stream

We are going to see in more detail only cout and cin (the standard output and input streams); cerr and clog are also output streams, so they essentially work like cout, with the only difference being that they identify streams for specific purposes: error messages and logging; which, in many cases, in most environment setups, they actually do the exact same thing: they print on screen, although they can also be individually redirected.

Standard output (cout):

=======================

cout << "Output sentence"; // prints Output sentence on screen

cout << 120;               // prints number 120 on screen

cout << x;                 // prints the value of x on screen  

Standard input (cin):

=====================

int age;

cin >> age; //Store the age in the cin input 

Example for the basic input and output:

======================================

// inputoutputexample.cpp

#include <iostream>

using namespace std;

int main ()

{

  int i;

  cout << "Please enter an integer value: ";

  cin >> i;

  cout << "The value you entered is " << i;

  cout << " and its double is " << i*2 << ".\n";

  return 0;

}

cin and strings: 

================

The extraction operator can be used on cin to get strings of characters in the same way as with fundamental data types:

1. string mystring;

2. cin >> mystring;

 //cinwithstrings.cpp ------------------------------------> Program 

#include <iostream>

#include <string>

using namespace std;

int main ()

{

  string mystr;

  cout << "What's your name? ";

  getline (cin, mystr);

  cout << "Hello " << mystr << ".\n";

  cout << "What is your favorite team? ";

  getline (cin, mystr);

  cout << "I like " << mystr << " too!\n";

  return 0;

}

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