<< Chapter < Page Chapter >> Page >
An introduction to the increment and decrement operators used in programming with details of C++ usage.

General discussion

The idea of increment or decrement is to either add or subtract 1 from a variable that is usually acting as a flag. Using a variable named counter; in generic terms, for example:

increment the counter

The concept is:

counter is assigned counter + 1

That is you fetch the existing value of the counter and add one then store the answer back into the variable counter. Many programming languages allow their increment and decrement operators to only be used with the integer data type. Programmers will sometimes use inc and dec as abbreviations for increment and decrement respectively.

Operator symbols and/or names vary with different programming languages. The C++ programming language operators with their meanings are:

C++ Operator Meaning
++ increment, two plus signs
-- decrement, two minus signs

C++ code examples

Basic concept

Within the C++ programming language the increment and decrement are often used in this simple generic way. The operator of increment is represented by two plus signs in a row. Examples:

counter = counter + 1;

counter += 1;

counter++;

++counter;

As C++ statements, the four examples all do the same thing. They add 1 to the value of whatever is stored in counter. The decrement opereator is represented by two minus signs in a row. They would subtract 1 from the value of whatever was in the variable being decremented. The precedence of increment and decrement depends on if the operator is attached to the right of the operand (postfix) or to the left of the operand (prefix). Within C++ postfix and prefix do not have the same precedence.

Postfix increment

Postfix increment says to use my existing value then when you are done with the other operators; increment me. An example:

int oldest = 44; // variable set up with initialization then later on in the codeage = oldest++;

The first use of the oldest variable is an Rvalue context where the existing value of 44 is pulled or fetched and then assigned to the variable age; then the variable oldest is incremented with its value changing from 44 to 45. This seems to be a violation of precedence because increment is higher precedence than assignment. But that is how postfix increment works within the C++ programming language.

Prefix increment

Prefix increment says to increment me now and use my new value in any calculation. An example:

int oldest = 44; // variable set up with initialization then later on in the codeage = ++oldest;

The variable oldest is incremented with the new value changing it from 44 to 45; then the new value is assigned to age.

In postfix age is assigned 44 in prefix age is assigned 45. One way to help remember the difference is to think of postfix as being polite (use my existing value and return to increment me after the other operators are done) where as prefix has an ego (I am important so increment me first and use my new value for the rest of the evaluations).

Allowable data types

Within some programming languages, increment and decrement can be used only on the integer data type. C++ however, expands this not only to all of the integer family but also to the floating-point family (float and double). Incrementing 3.87 will change the value to 4.87. Decrementing 'C' will change the value to 'B'. Remember the ASCII character values are really one byte unsigned integers (domain from 0 to 255).

Exercises

    Evaluate the following items using increment or decrement:

  1. True or false: x = x +1 and x+=1 and x++ all accomplish increment?
  2. Given: int y = 19; and int z; what values will y and z have after: z = y--;
  3. Given: double x = 7.77; and int y; what values will x and y have after: y = ++x;
  4. Is this ok? Why or why not? 6 * ++(age -3)

    Answers:

  1. true
  2. y is: 18 and z is: 19
  3. x is: 8.77 and y is: 8 Note: truncation of 8.77 to 8 upon demotion.
  4. Not ok. Error, the item incremented must have Lvalue attributes, usually a variable. It is an expression not a variable.
Got questions? Get instant answers now!

Definitions

increment
Adding one to the value of a variable.
decrement
Subtracting one from the value of a variable.
postfix
Placing the increment or decrement operator to the right of the operand.
prefix
Placing the increment or decrement operator to the left of the operand.

Questions & Answers

what is mutation
Janga Reply
what is a cell
Sifune Reply
how is urine form
Sifune
what is antagonism?
mahase Reply
classification of plants, gymnosperm features.
Linsy Reply
what is the features of gymnosperm
Linsy
how many types of solid did we have
Samuel Reply
what is an ionic bond
Samuel
What is Atoms
Daprince Reply
what is fallopian tube
Merolyn
what is bladder
Merolyn
what's bulbourethral gland
Eduek Reply
urine is formed in the nephron of the renal medulla in the kidney. It starts from filtration, then selective reabsorption and finally secretion
onuoha Reply
State the evolution relation and relevance between endoplasmic reticulum and cytoskeleton as it relates to cell.
Jeremiah
what is heart
Konadu Reply
how is urine formed in human
Konadu
how is urine formed in human
Rahma
what is the diference between a cavity and a canal
Pelagie Reply
what is the causative agent of malaria
Diamond
malaria is caused by an insect called mosquito.
Naomi
Malaria is cause by female anopheles mosquito
Isaac
Malaria is caused by plasmodium Female anopheles mosquitoe is d carrier
Olalekan
a canal is more needed in a root but a cavity is a bad effect
Commander
what are pathogens
Don Reply
In biology, a pathogen (Greek: πάθος pathos "suffering", "passion" and -γενής -genēs "producer of") in the oldest and broadest sense, is anything that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ. The term pathogen came into use in the 1880s.[1][2
Zainab
A virus
Commander
Definition of respiration
Muhsin Reply
respiration is the process in which we breath in oxygen and breath out carbon dioxide
Achor
how are lungs work
Commander
where does digestion begins
Achiri Reply
in the mouth
EZEKIEL
what are the functions of follicle stimulating harmones?
Rashima Reply
stimulates the follicle to release the mature ovum into the oviduct
Davonte
what are the functions of Endocrine and pituitary gland
Chinaza
endocrine secrete hormone and regulate body process
Achor
while pituitary gland is an example of endocrine system and it's found in the Brain
Achor
what's biology?
Egbodo Reply
Biology is the study of living organisms, divided into many specialized field that cover their morphology, physiology,anatomy, behaviour,origin and distribution.
Lisah
biology is the study of life.
Alfreda
Biology is the study of how living organisms live and survive in a specific environment
Sifune
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




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