Post-increment and Pre-increment concept?

Question

I don't understand the concept of postfix and prefix increment or decrement. Can anyone give a better explanation?

Answer 1

The pre increment is before increment value ++ e.g.:

(++v) or 1 + v

The post increment is after increment the value ++ e.g.:

(rmv++) or rmv + 1

Program:

int rmv = 10, vivek = 10;
cout << "rmv++ = " << rmv++ << endl; // the value is 10
cout << "++vivek = " << ++vivek; // the value is 11

Answer 2

You should also be aware that the behaviour of postincrement/decrement operators is different in C/C++ and Java.

Given

  int a=1;

in C/C++ the expression

 a++ + a++ + a++

evaluates to 3, while in Java it evaluates to 6. Guess why...

This example is even more confusing:

cout << a++ + a++ + a++ << "<->" << a++ + a++ ;

prints 9<->2 !! This is because the above expression is equivalent to:

operator<<( 
  operator<<( 
    operator<<( cout, a++ + a++ ), 
    "<->"
  ), 
  a++ + a++ + a++ 
)

Answer 3

No one has answered the question: Why is this concept confusing?

As an undergrad Computer Science major it took me awhile to understand this because of the way I read the code.

The following is not correct!

---

x = y++

X is equal to y post increment. Which would logically seem to mean X is equal to the value of Y after the increment operation is done. Post meaning after.

or

x = ++y
X is equal to y pre-increment. Which would logically seem to mean X is equal to the value of Y before the increment operation is done. Pre meaning before.

---

The way it works is actually the opposite. This concept is confusing because the language is misleading. In this case we cannot use the words to define the behavior.
x=++y is actually read as X is equal to the value of Y after the increment.
x=y++ is actually read as X is equal to the value of Y before the increment.

The words pre and post are backwards with respect to semantics of English. They only mean where the ++ is in relation Y. Nothing more.

Personally, if I had the choice I would switch the meanings of ++y and y++. This is just an example of a idiom that I had to learn.

If there is a method to this madness I'd like to know in simple terms.

Thanks for reading.