How to replace an array strng?

sgtpepper

Hello,

I have a php checkboxes that contain days of the week:

[ ] Sun [ ] Mon [ ] Tue etc....

In my database I have a field that seperates the days with commas like this:

0,1,0,0,0,1,0

Basically, it is like binary code. 0 means that Sun is NOT checked.....1 means that Monday IS checked.

I want to give the end user the ability to check days on or off. How can I setup the array to replace the data?

For example;

Lets say I have the following days checked....

0,1,0,0,0,1,0

but the user decides to UNCHECK monday....

0,0,0,0,0,1,0

how should I setup the form and query to update the change?

I am using the following array scheme to pre-fill the checkboxes.

if ( $_POST[days] [0] == 'Sun' ) {
$checked0 = "checked";
} else {
$checked0 = "";
}

if ( $_POST[days][1] == 'Mon' ) {
$checked1 = "checked";
} else {
$checked1 = "";
}

if ( $_POST[days][2] == 'Tue' ) {
$checked2 = "checked";
} else {
$checked2 = "";
}

if ( $_POST[days][3] == 'Wed' ) {
$checked3 = "checked";
} else {
$checked3 = "";
}

if ( $_POST[days][4] == 'Thu' ) {
$checked4 = "checked";
} else {
$checked4 = "";
}

if ( $_POST[days][5] == 'Fri' ) {
$checked5 = "checked";
} else {
$checked5 = "";
}

if ( $_POST[days][6] == 'Sat' ) {
$checked6 = "checked";
} else {
$checked6 = "";
}

madwormer2

"It's like binary"

Why not use binary?

Example:

Set all the days a no.:

Sun: 1, Mon: 2, Tue: 4, Wed: 8, Thur: 16, Fri: 32, Sat: 64.

Then, add all the SELECTED ones, like so:

Monday + Tuesday + Wednesday = 14

Now, how do we check what's selected? Simple:

$total = 14;
if($total & 2){
 echo 'Monday is checked';
}else{
echo 'Not checked';
}

How do we toggle something on, to something off? Easy:

$total = 14;
if(!($total & 64)){ // if saturday is off
$total=$total + 64; // Saturday is now on.
}

// And to turn it off...

$total = 14;
if(!($total & 2)){ // if monday is on
$total=$total -2; // Monday is now off.
}

What's happening here is we're using the binary code, and the & symbol to check if each one is set:

14 is - 0001110

We check to see if 2 is on, which actually checks this digit: 0001110 if it's one, then all is cool :p

I'm sure there's a better tutorial on the internet somewhere, however :p

bpat1434

Wow.... i really need to learn the bitwise operations... that's pretty slick Madwormer....

madwormer2

Heh, I said "I really need to learn the bitwise operators" when I read his post 😉

So I went away and learnt them. (Well, I sorta learnt them before, but could never get it to work.

And it's pretty cool that you can store seven bits of information in a 2 or 3 digit number.

Oh, when I said "assign them a number" those numbers are used for a very specific reason lol.

bpat1434

I knew why you did
1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384 . . .

I just need to learn the bitwise operators and exactly what one does.....

And yes... I can count to 31 on 1 hand . . .

madwormer2

Lol, no, that comment was for the topic starter, because I'm pretty sure he's never even heard of them before...

http://uk.php.net/manual/en/language.operators.bitwise.php

Weedpacket

And to make the code more readable:

define('SUNDAY',1<<0);
define('MONDAY',1<<1);
...
define('SATURDAY',1<<6);

madwormer2

I wasn't aware you could do 1<<2 to shift it two to the left. Still learning, always learning...

Rodney_H_

/ Off Topic /

sgtpepper wrote:
Are Oomba-Loomba's A-Sexual?

If you are talking about the characters in Roald Dahl's Book, "Charlie and the Chocolate Factory", I believe they are in fact "Oompa Loompas".

🙂

bpat1434

Warn... Warn.... WARN!!!!

Care to explain that 1<<2 or 1<<6 shift?

madwormer2

Yup.

1 is:

0000001

1<<2 shifts it 2 to the left:

0000100 - this is now 4.

1<<6 shifts it 6 to the leftt:

1000000 - this is now 64

Weedpacket

In other words "<<" is short for "times two to the power of". Just like the "e" in "5.5e3" is short for "times ten to the power of".

Rodney_H_

Weedpacket wrote:
In other words "<<" is short for "times two to the power of". Just like the "e" in "5.5e3" is short for "times ten to the power of".

Totally cool, Weedpacket.

bpat1434

Wicked.....

4 << 2 == 4 ( 2 ² ) = 16
10<<12 == 10 ( 2 ¹² ) = 40960

Right... so I'd be safe in assuming:

[a] >> == a divided by ( 2 ^b )?
4 >> 1 = 2
8 >> 2 = 2
24 >> 3 = 3
1024 >> 7 = 8

Is that correct? Not necessarily the math, but the general idea that it's a right-shift vs a left-shift?

Weedpacket

That's the general idea (you could, after all, try it 🙂). The biggest difference between $foo>>1 and $foo/2 of course is in how they handle odd values of $foo.

madwormer2

Although you can't shift any values past the end, otherwise they disappear.

So... 3>>1 is actually 1.

Because....

00000011 >> 00000001[1] the end one is cut off, leaving only one.

In all these binary examples I should probably be using 8 digits, such is a byte. Just so you know.