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Standard I/O within C++

5 February, 2015 - 16:57

The developers of the C++ programming language decided to provide some of the more technical code needed to interact with the operating system and the I/O devices. In the following example the include directive inserts a file that contains code from the Input-Output Stream library. This file contains necessary code to use cout and cin for sending data to the monitor or getting data from the keyboard.

#include <iostream>

You should think of cout and cin as being locations that you can send to or receive data from; similar in concept to any other variable storage location within the data area of our program. The C++ programming language has two operators to use in conjunction with I/O devices.


C ++ operator symbol

Used with

insertion operator (write)

« (a pair of less than symbols)


extraction operator (read)

» (a pair of greater than symbols)


Consider the following code:

Example 5.1: Insertion and Extraction

int agel;     // variable set up     then later on in our program cout « "\nEnter the age of the first person --->: "; cin »  agel; 

Using the cout the programmer displays (or inserts) a prompting message on the monitor for the user to see. Using the cin the user types an integer value and hits the enter key and the computer extracts the value from the keyboard and stores it into the variable named age1. Within the computer all data are stored as numbers and thus part of the technical code provided by the developers of the C++ programming language that is within the Input-Output Stream library converts data from numbers to those symbols we are used to seeing as humans and vice versa. Example: If the user entered the numeral digits 57 and hit the enter key the extraction operator would convert the 57 into a binary number and move the binary number into the integer storage place named age1.

The cout which uses the standard output device does not format the output into a Graphical User Interface (GUI) where you have a mouse to use. A modern operating system using GUI normally opens a black screen output box that would be similar to how the monitor was used when first developed in the 1960's. That is the default of how cout is normally implemented by most compilers.

The output message has a unique item worth mentioning. At the very front of the message is a backslash followed by the letter n. They do not get printed on the monitor. It is a special code (called a printer escape code) telling the printer to go to a new line. Printer! I thought we were using a monitor? We are but the code is a left over from the early days of printer output. The backslash tells the printer or monitor that the next letter is a command. The letter n is used for telling the printer or monitor to go to the front of a new line.