# Thread: Question about auto increment auto decrement unary operator syntax

1. Registered User
Join Date
Mar 2012
Posts
34

## Question about auto increment auto decrement unary operator syntax

If I run the following code in firebug the output equals 0
Code:
```y = 5;
x = 0;
z = 1;
newnum = y++ + ++x + x++ + z++ - z++ - y--;```
If I test x, y and z on their own in firebug the output is -

Code:
```y++;   //  5
++x;  // 1
x++;  // 0
z++;  // 1
y--;   // 5```
this makes newnum look like

newnum2 = 5 + 1 + 0 + 1 - 1 - 5; // which outputs 1 in firebug

Is there a particular reason the output of newnum is 0 rather than 1?

Best regards Maxwell

2. y = 5;
x = 0;
z = 1;

newnum = y++ + ++x + x++ + z++ - z++ - y--;

in human language this means:
(return y which is 5, then do y+1) ---------> 5
+
(do x+1, then return x) ---------> 1
+
(return x, then do x + 1) ---------> 1
+
(return z, then do z+1) ---------> 1
-
(return z, then do z+1) ---------> 2
-
(return y, then do y-1) ---------> 6

so we have 5+1+1+1-2-6=0

3. Registered User
Join Date
Mar 2012
Posts
34
I still don't understand how y-- can equal 6 when it originally contained 5

4. Registered User
Join Date
Oct 2010
Location
Versailles, France
Posts
1,290
Y was originally 5, but it has been modified to 6 !

5. again. we have

y = 5;
x = 0;
z = 1;

newnum = y++ + ++x + x++ + z++ - z++ - y--;

y++ means: take var y (which is 5 now) for the newnum math adding operation, then increase it by 1
the same with all var++
but
++x means: increase x by 1, then take it (being 1 now, not 0) for the newnum math adding operation
Last edited by Padonak; 06-15-2013 at 12:51 AM.

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