Incrementing / Decrementing Operators
++ increment operator
— decrement operator
Example Name Effect
———————————————————————
++$a Pre-increment Increments $a by one, then returns $a.
$a++ Post-increment Returns $a, then increments $a by one.
–$a Pre-decrement Decrements $a by one, then returns $a.
$a– Post-decrement Returns $a, then decrements $a by one.
These can go before or after the variable.
If put before the variable, the increment/decrement operation is done to the variable first then the result is returned. If put after the variable, the variable is first returned, then the increment/decrement operation is done.
For example:
$apples = 10;
for ($i = 0; $i < 10; ++$i) {
echo 'I have ' . $apples-- . " apples. I just ate one.n";
}
Live example
In the case above ++$i is used, since it is faster. $i++ would have the same results.
Pre-increment is a little bit faster because it really increments the variable and after that 'returns' the result. Post-increment creates a special variable, copies there the value of the first variable and only after the first variable is used, replaces its value with second's.
However, you must use $apples--, since first, you want to display the current number of apples, and then you want to subtract one from it.
You can also increment letters in PHP:
$i = "a";
while ($i < "c") {
echo $i++;
}
Once z is reached aa is next, and so on.
Note that character variables can be incremented but not decremented and even so only plain ASCII characters (a-z and A-Z) are supported.
Stack Overflow Posts:
Understanding Incrementing
Bitwise Operator
What is a bit? A bit is a representation of 1 or 0. Basically OFF(0) and ON(1)
What is a byte? A byte is made up of 8 bits and the highest value of a byte is 255, which would mean every bit is set. We will look at why a byte's maximum value is 255.
-------------------------------------------
| 1 Byte ( 8 bits ) |
-------------------------------------------
|Place Value | 128| 64| 32| 16| 8| 4| 2| 1|
-------------------------------------------
This representation of 1 Byte
1 + 2 + 4 + 8 + 16 + 32 + 64 + 128 = 255 (1 Byte)
A few examples for better understanding
The "AND" operator: &
$a = 9;
$b = 10;
echo $a & $b;
This would output the number 8. Why? Well let's see using our table example.
-------------------------------------------
| 1 Byte ( 8 bits ) |
-------------------------------------------
|Place Value | 128| 64| 32| 16| 8| 4| 2| 1|
-------------------------------------------
| $a | 0| 0| 0| 0| 1| 0| 0| 1|
-------------------------------------------
| $b | 0| 0| 0| 0| 1| 0| 1| 0|
-------------------------------------------
| & | 0| 0| 0| 0| 1| 0| 0| 0|
-------------------------------------------
So you can see from the table the only bit they share together is the 8 bit.
Second example
$a = 36;
$b = 103;
echo $a & $b; // This would output the number 36.
$a = 00100100
$b = 01100111
The two shared bits are 32 and 4, which when added together return 36.
The "Or" operator: |
$a = 9;
$b = 10;
echo $a | $b;
This would output the number 11. Why?
-------------------------------------------
| 1 Byte ( 8 bits ) |
-------------------------------------------
|Place Value | 128| 64| 32| 16| 8| 4| 2| 1|
-------------------------------------------
| $a | 0| 0| 0| 0| 1| 0| 0| 1|
-------------------------------------------
| $b | 0| 0| 0| 0| 1| 0| 1| 0|
-------------------------------------------
| | | 0| 0| 0| 0| 1| 0| 1| 1|
-------------------------------------------
You will notice that we have 3 bits set, in the 8, 2, and 1 columns. Add those up: 8+2+1=11.