<< Chapter < Page Chapter >> Page >
Implicit and explicit type conversion with both promotion and demotion is discussed with some examples.

Overview

Changing a data type of a value is referred to as "type conversion".  There are two ways to do this:

  1. Implicit – the change is implied
  2. Explicit – the change is explicitly done with the cast operator

The value being changed may be:

  1. Promotion – going from a smaller domain to a larger domain
  2. Demotion – going from a larger domain to a smaller domain

Implicit type conversion

Automatic conversion of a value from one data type to another by a programming language, without the programmer specifically doing so, is called implicit type conversion.  It happens when ever a binary operator has two operands of different data types. Depending on the operator, one of the operands is going to be converted to the data type of the other. It could be promoted or demoted depending on the operator.

Implicit promotion

55 + 1.75

Got questions? Get instant answers now!

In this example the integer value 55 is converted to a floating-point value (most likely double) of 55.0. It was promoted.

Implicit demotion

int money; // variable set up then later in the programmoney = 23.16;

Got questions? Get instant answers now!

In this example the variable money is an integer. We are trying to move a floating-point value 23.16 into an integer storage location. This is demotion and the floating-point value usually gets truncated to 23.

Promotion

Promotion is never a problem because the lower data type (smaller range of allowable values) is sub set of the higher data type (larger range of allowable values).  Promotion often occurs with three of the standard data types: character, integer and floating-point. The allowable values (or domains) progress from one type to another.  That is the character data type values are a sub set of integer values and integer values are a sub set of floating-point values; and within the floating-point values: float values are a sub set of double.  Even though character data represent the alphabetic letters, numeral digits (0 to 9) and other symbols (a period, $, comma, etc.) their bit pattern also represent integer values from 0 to 255.  This progression allows us to promote them up the chain from character to integer to float to double.

Demotion

Demotion represents a potential problem with truncation or unpredictable results often occurring.  How do you fit an integer value of 456 into a character value?  How do you fit the floating-point value of 45656.453 into an integer value? Most compilers give a warning if it detects demotion happening. A compiler warning does not stop the compilation process. It does warn the programmer to check to see if the demotion is reasonable.

If I calculate the number of cans of soup to buy based on the number of people I am serving (say 8) and the servings per can (say 2.3), I would need 18.4 cans. I might want to demote the 18.4 into an integer. It would truncate the 18.4 into 18 and because the value 18 is within the domain of an integer data type, it should demote with the truncation side effect.

If I tried demoting a double that contained the number of stars in the Milky Way galaxy into an integer, I might have a get an unpredictable result (assuming the number of stars is larger than allowable values within the integer domain).

Explicit type conversion

Most languages have a method for the programmer to change or cast a value from one data type to another; called explicit type conversion .  Within C++ the cast operator is a unary operator; it only has one operand and the operand is to the right of the operator. The operator is a set of parentheses surrounding the new data type.

Explicit demotion with truncation

(int) 4.234

Got questions? Get instant answers now!

This expression would evaluate to: 4.

Demonstration program in c++

Creating a folder or sub-folder for source code files

Depending on your compiler/IDE, you should decide where to download and store source code files for processing. Prudence dictates that you create these folders as needed prior to downloading source code files. A suggested sub-folder for the Bloodshed Dev-C++ 5 compiler/IDE might be named:

  • Demo_Programs

If you have not done so, please create the folder(s) and/or sub-folder(s) as appropriate.

Download the demo program

Download and store the following file(s) to your storage device in the appropriate folder(s). Following the methods of your compiler/IDE, compile and run the program(s). Study the soruce code file(s) in conjunction with other learning materials.

Download from Connexions: Demo_Data_Type_Conversions.cpp

Definitions

implicit
A value that has its data type changed automatically.
explicit
Changing a value's data type with the cast operator.
promotion
Going from a smaller domain to a larger domain.
demotion
Going from a larger domain to a smaller domain.
truncation
The fractional part of a floating-point data type that is dropped when converted to an integer.

Questions & Answers

what is the stm
Brian Reply
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
How can I make nanorobot?
Lily
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
how can I make nanorobot?
Lily
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!





Source:  OpenStax, Programming fundamentals - a modular structured approach using c++. OpenStax CNX. Jan 10, 2013 Download for free at http://cnx.org/content/col10621/1.22
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Programming fundamentals - a modular structured approach using c++' conversation and receive update notifications?

Ask