Why does ++ not add one to integer value

Question

I have the following lines on my code:

   Log.d ("Playlist", "Current Song Number is: "+ currentSongNumber );

   currentSongNumber = currentSongNumber++;

   Log.d ("Playlist", "Current Song Number has changed to: "+ currentSongNumber );

But i get the result:

Current Song Number is: 2
Current Song Number has changed to: 2

So why has it not chaged to three does ++ only work when iterating?

It will read the current value 2, increment to 3 and then assign the previously read value 2 again. — Thomas, Jun 17 '16 at 09:32
Java's basics differences between var++ and ++var and assignment http://ideone.com/L4yx7d — Selvin, Jun 17 '16 at 09:32

score 4 · Accepted Answer · answered Jun 17 '16 at 09:35

The post-increment operator returns the old value and then it increments. By assigning back to the same variable, you discard the increment done to the variable.

So when you do

currentSongNumber = currentSongNumber++;

it is equivalent to the following code:

int oldValueOfCurrentSongNumber = currentSongNumber;
currentSongNumber = currentSongNumber + 1;
currentSongNumber = oldValueOfCurrentSongNumber;  // This is because of your assignment

why it assigning old value – Nouman Shah Jun 17 '16 at 10:02 — Nouman Shah, Jun 17 '16 at 10:02

score 1 · Answer 2 · answered Jun 17 '16 at 09:33

1

Try just this code: currentSongNumber++;

answered Jun 17 '16 at 09:33

Amine Rankeno

11
2

score 1 · Answer 3 · answered Jun 17 '16 at 09:33

1

Because you are using post increment

so either try this

currentSongNumber = ++currentSongNumber;

or this

currentSongNumber++;

or this

++currentSongNumber;

answered Jun 17 '16 at 09:33

Manish Menaria

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score 1 · Answer 4 · edited May 23 '17 at 11:45

1

You are using post increment. Click here to see the difference between pre-increment and post increment. In your code try pre increment.

++currentSongNumber;

This will give you desired output.

In your code, If you use currentSongNumber = currentSongNumber++; than first the value of currentSongNumber will be assigned to itself, which is same as previous and than the increment will take place.

Or you can just use simply currentSongNumber = currentSongNumber+1;, to avoid confusions.

edited May 23 '17 at 11:45

Community

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answered Jun 17 '16 at 09:33

Kaushal28

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`++` is syntactic sugar which allows to write only `currentSongNumber++`. You should not encourage the OP to write this useless affectation. `++currentSongNumber` or `currentSongNumber++` is enough here. – Arnaud Denoyelle Jun 17 '16 at 09:35

score 1 · Answer 5 · answered Jun 17 '16 at 10:06

1

Just try this at home:

Log.d ("Playlist", "Current Song Number is: "+ currentSongNumber );

  currentSongNumber++;

   Log.d ("Playlist", "Current Song Number has changed to: "+ currentSongNumber );

answered Jun 17 '16 at 10:06

Saeed Sharman

765
5
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Why does ++ not add one to integer value

5 Answers5