I'm having trouble with a switch case conidtion.
Why in the following scenario:
$category = "A";
$offer = "none";
$discount = "none";
For the following code:
switch (TRUE) {
case ($category == 'A') : / #1
$msg = "hello";
case ($offer == 'special') : / #2
$id = "123";
case ($discount == '50D') : / #3
$id = "999";
break;
echo $id;
}
I get output of 999 for id, even though #2 and #3 are not fullfilled?
EDIT:
Cases such as $offer == 'special' are private cases of the general case which is $category == 'A'.
That's why I want the function to go in this order.
if switch/case is not appropriate, what shall I use?
Once switch finds a matching case, it just executes all the remaining code until it gets to a break statement. None of the following case expressions are tested, so you can't have dependencies like this. To implement sub-cases, you should use nested switch or if statements.
switch ($category) {
case 'A':
$msg = 'hello';
if ($offer == 'special') {
$id = '123';
} elseif ($discount == '50D') {
$id = '999';
}
break;
...
}
echo $id;
The fallthrough feature of case without break is most often used when you have two cases that should do exactly the same thing. So the first one has an empty code with no break, and it just falls through.
switch ($val) {
case 'AAA':
case 'bbb':
// some code
break;
...
}
It can also be used when two cases are similar, but one of them needs some extra code run first:
switch ($val) {
case 'xxx':
echo 'xxx is obsolete, please switch to yyy';
case 'yyy':
// more code
break;
...
}
This is how a switch-case statement works. It goes through all the casees once one condition was met, as long as there is no break. You can read up on it in the manual here: PHP switch.
If you want to stop the execution of the switch at the end of an case, just add a break; statement.
Related
I have this simple function to convert the number of comments of an user to types of members.
function checkMemberN($numMessages){
$n= $numMessages;
switch ($n) {
case ($n<50): $type="New"; break;
case ($n>=50 && $n<250):$type="Frequent";break;
case ($n>=250 && $n<1000): $type="Master";break;
default: $type="undefinded";
}
return $type;
}
echo checkMemberN(0);
It looks like it doesn't recognize zero (0), because when I put 1 or a higher number it retrieves the correct user type. What am I doing wrong?
When you use switch, the first case which returns a value equal to the given one is selected. In this case, your argument (zero) is a false-y value. That's why the first case that returns false is chosen: "Frequent".
To fix it, you can do this:
if ($n<50) {
$type = "New";
} else if ($n>=50 && $n<250) {
$type = "Frequent";
} else if ($n>=250 && $n<1000) {
$type = "Master";
} else {
$type = "undefined";
}
If you still want to use switch, you can change the argument to true:
switch (true) {
case ($n<50): $type="New"; break;
case ($n>=50 && $n<250):$type="Frequent";break;
case ($n>=250 && $n<1000): $type="Master";break;
default: $type="undefinded";
}
Here, the first case which returns true will be used.
in PHP (and even other languages but in the present case this is more for PHP), i often end up sometimes having to code long conditions such as the example below:
i have a code with many conditions and i want to display a different result based on certain conditions.
if something is RED and the other thing is RED, then print X,
if something is RED but the other thing is BLACK, then print Y
if something RED and the other thing is RED but a third thing is blue, then print X
& so on
is there a way to properly handle this by using some kind of data structure/configuration array/matrix/whatever ? that is, storing these "conditions" and "results" properly in some kind of configuration array or other ?
instead of having to code nested conditions that can be tricky to support afterwards
like this very small example but in a much bigger scale
if (preg_match(/something/, $string) {
$result = 'GREEN';
} elseif (preg_match(/something/, $string) {
$result = 'RED';
} else {
if (something else) {
$result = 'GREEN';
} else {
if (something OR something) {
$result = 'AMBER';
} else {
$result = 'GREEN';
}
}
}
or is it the only way of handling this ?
maybe with a single
if (something and something or something) {
} elseif (something and something and something) {
} elseif (something and something or something and something) {
} etc
thank you for your help
i'm coding an app that should display a different "status" for a certain data depending on many different data (other attributes of this data), and i'd like to avoid having unreadable code
You can use nested arrays:
$conditions = [
'/something1/' => [
'/something2/' => "X"
],
'thing3' => [
'/thing3/' => 'Y',
'/thing4/' => 'Z'
]
];
$matched = false;
foreach ($conditions as $key1 => $val1) {
if (preg_match($key1, $string)) {
if (is_array($val1)) {
foreach ($val1 as $key2 => $val2) {
if (preg_match($key2, $string)) {
$result = $val2;
$matched = true;
break;
}
}
} else {
$result = $val1;
$matched = true;
}
}
if ($matched) {
break;
}
}
if (!$matched) {
$result = 'default';
}
To allow arbitrary levels of nesting you could turn this into a recursive function.
For the purposes of the answer below I'm assuming you're coding OO PHP.
One variable
When I have one variable that determines the outcome, if the variable is boolean or close to being boolean (meaning it can only either be one or two different values), is to use an if() statement like you have. If the variable can be a variety of (known) values, like your colours example, I use a switch() function.
Two or more variables
If I have two variables that determine the outcome, for instance colour and size, I first use a switch(), then for each switch, I use a method that contains another switch().
It may be more verbose, but it is so much easier to keep track of in the long run. Below is a simplified example of the logic.
switch ($colour) {
case 'red':
red_handler($size);
break;
case 'green':
green_handler($size);
break;
case 'blue':
blue_handler($size);
break;
}
/** We already know the first variable value is red */
function red_handler($size)
{
switch ($size) {
case 'small':
echo "my fruit is a cherry";
break;
case 'medium':
echo "my fruit is an apple";
break;
case 'large':
echo "my fruit is a watermelon";
break;
}
}
In a similar vein to #dearsina i'd tend to separate it out into functions for this kind of thing, for example if you know there are lots of cases where it could return the same value, e.g.:
if(isGreen($string)) return 'GREEN';
else if (isRed($string)) return 'RED';
function isGreen($string) {
if(cond1)return true;
if(cond2 && cond3)return true;
if(cond4 || cond 5)return true;
return false;
}
function isRed($string) {
if(cond6)return true;
if(cond1 && cond7)return true;
if(cond2 || cond 8)return true;
return false;
}
we do sometimes use the style you've suggested...
if (something and something or something) {
} else if (something and something and something) {
but you can quickly end up back in the same problems of readability and maintenance issues
I have a large switch statement in my code, and I want it to do something like this:
// assign $foo
switch ($foo) {
case 1:
case 2:
// do X, then break if 1, do Y and break if 2
case 3:
case 4:
case 5:
// do A & B, break if 3, do C if 4 or 5, do D if 5 and then break
}
Such "groups" are prevalent throughout the switch statement and currently I just repeat the logic, keeping each case separate.
Am I wrong in assuming that this could be restructured into something that's objectively "better"?
Edit: I excluded my original code snippet from the question, since it had deeply flawed logic and didn't conform to the basic concepts of using a switch, replacing it with pseudocode that resembles the desired result.
As commented, that switch doesn't actually work as you think.
You're simply looking for:
if (in_array($foo, [1, 2])) {
...
if ($foo == 2) {
...
}
}
Alternatively:
switch ($foo) {
case 1:
case 2:
...
if ($foo == 2) {
...
}
break;
}
TLDR;
For simple "is it this", use a switch, if you need logical checks, use an if
The answer;
What you are asking is quite subjective, while using a switch for something simple is good, i.e;
<?php
$case = getCaseFrom("X"); // Let's say this = "a"
switch ($case)
{
case "a" : {
$thing = "a";
break;
}
case "b" : {
$thing = "b";
break;
}
case "c" : {
$thing = "c";
break;
}
default : {
$thing = "d";
}
}
?>
The same could be achieved by using;
<?php
$case = getCaseFrom("x");
$thing = $case;
// And even shorter;
$thing = getCaseFrom("x");
?>
Whereas, if you needed some logic to this...
<?php
$operator = getOperatorFrom("X"); // In this case, add
$num1 = 10;
$num2 = 2;
switch ($operator)
{
case "add" : {
$res = num1 + num2;
break;
}
case "subtract" : {
$res = num1 - num2;
break;
}
case "multiply" : {
$res = num1 * num2;
break;
}
case "divide" : {
$res = num1 / num2;
break;
}
}
?>
The alternative;
And of course, all of the above switches case be done using if else clauses, but a switch (IMO) is a neater, and more readable approach depending on what your certain criteria are (see the drawbacks).
The easiest way to look at it is;
If you need to check if something matches a value, use an if, if it is an enumerated set of values (let's say 1 to 4), a switch is subjectively better
The drawbacks;
A switch also doesn't let you have multiple "and" checks in the same statement, for example;
<?php
$case = getCaseFrom("X"); // In this case, a (does not have "b")
switch ($case)
{
case "a" :
case "b" : {
// This checks for a or b, not both, despite this not containing "b"
// this will still be accessed
break;
}
case "c" : {
// This will not be used as the break stops
// it from falling through to this clause
break;
}
}
if (stristr("a", $case) && stristr("b", $case))
{
// This checks to see if case contains a AND b
// therefore, this will not be used, as this
// does not have both a and b in $case
}
else if (stristr("a", $case) || stristr("b", $case))
{
// This checks to see if case contains a OR b
// therefore, this will be used, as this
// is checking that $case has "a" or "b" in it
// This is the same as the switch in this instance as it uses "or"
}
The noteworthy;
To be aware of the following also would be useful;
Inside a switches case, you cannot use login, for example;
case getThing("a") :
would cause an error
NB: Of course, when using the case statements, you don't need the curly braces added, they are mainly for code folding and ease of reading
--Let me add this. This code works for me the way it is. I just do not know why it works.--
I can't figure this out.
switch ($_SERVER['QUERY_STRING']) {
case isset($_GET['test0']):
echo "test0<br>";
break;
case isset($_GET['test1']):
echo "test1<br>";
break;
case isset($_GET['test2']):
echo "test2<br>";
break;
case isset($_GET['test3']):
echo "test3<br>";
break;
case isset($_GET['test4']):
echo "test4<br>";
break;
default:
echo "no test<br>";
break;
}
When the url is index.php?test0, "test0" is shown.
When the url is index.php?test4, "test4" is shown.
When the url is index.php?test999, "no test" is shown.
When the url is index.php?tes, "no test" is shown.
When the url is index.php?, or index.php, "test0" is shown.
Why is this? The condition is not met, so should the default not be shown?
switch can't be used this way. isset() returns true or false, not something (a string, an int, etc) you can match against. What you are basically doing is:
switch ($_SERVER['QUERY_STRING']) {
case true:
echo "test0<br>";
break;
case true:
echo "test1<br>";
break;
case false:
echo "test2<br>";
break;
case false:
echo "test3<br>";
break;
case true:
echo "test4<br>";
break;
default:
echo "no test<br>";
break;
}
cases are considered from top to bottom. In this case, $_SERVER["QUERY_STRING"] is automatically type-converted to bool (which will return true in this case). The first case it sees would be test0, so it echos that. If you do that for test0-4, it will give you the false illusion that this code is working as intended, while it's not considering the edge cases.
The only way you can achieve what you want is by using multiple ifs, or by redesigning your application.
When the url is index.php?, or index.php, "test0" is shown.
Why is this? The condition is not met, so should the default not be shown?
Like a good question, your question as well contains the answer already.
You already have realized that the condition must be met even you think it is not met. Therefore you ask. So let's see which condition is met:
case isset($_GET['test0']):
echo "test0<br>";
break;
This is a test for isset($_GET['test0']) and we know with the request that this is FALSE. So this test tests for FALSE.
Now let's see against what this tests:
switch ($_SERVER['QUERY_STRING']) {
That is $_SERVER['QUERY_STRING']. So if $_SERVER['QUERY_STRING'] is FALSE the test0 will be output.
Because switch { case:} in PHP does loose comparison, the empty string $_SERVER['QUERY_STRING'] is FALSE. This is why you see the output.
Easy if you know why, right? And all so logical.
And what you wanted to test against was not $_SERVER['QUERY_STRING'] but just TRUE:
switch (TRUE)
{
case isset($_GET['test0']) :
...
}
This gets the job done, too.
<?php
$q = $_SERVER['QUERY_STRING'];
if(!empty($q) && isset($q) && strlen($q) >0 ){
$url = $q;
switch ($url){
case true;
echo $url;
break;
}
}
else {
echo "no test<br>";
}
what about
$found = false;
for($i=0;$i <=4; $i++){
if( isset($_GET['test'.$i]) ){
echo "test".$i;
$found = true;
}
}
if(!$found){
echo "no test";
}
Let's take a look at the following code:
if ($a == 1) {
echo "this is stage 1";
}
else if ($a == 2) {
echo "this is stage 2";
}
else if ($a == 3) {
$a = 1;
// at this point I want something that restarts the if-else construct so
// that the output will be "this is stage 1"
}
I'm working on an if else construct at the moment and let's say that I have three stages and the if-else construct checks which stage I'm in.
Now it happens that some activities in stage 3 lead to a jump back to stage 1. Now I've already passed the code for stage one, which is why I want to somehow restart the if-else construct. Is there a way to do that? And even more important: Is there a better way to do what I want? Because my idea doesn't seem to be good practice.
You're right, it's bad practice.
You're asking for goto.
Example:
<?php
goto a;
echo 'Foo';
a:
echo 'Bar';
The above would never output 'Foo'
It's difficult to suggest the better method without seeing exactly what you're trying to do, but consider a switch.
switch ($a) {
case 3:
// Execute 3 stuff
// No break so it'll continue to 1
case 1:
// Execute 1 stuff
break // Don't go any further
case 2:
// 2 stuff
break;
}
That's probably not what you want either.
You may just want to abstract the code into functions and call them multiple times if necessary.
You can put an endless loop around your if and break out if you're done
while (1) {
if ($a == 1) {
echo "this is stage 1";
break;
}
else if ($a == 2) {
echo "this is stage 2";
break;
}
else if ($a == 3) {
$a = 1;
}
else {
break;
}
}
Maybe you want to look at Wikipedia - Finite-state machine and this question PHP state machine framework
The short answer is yes, there is a way, but the better answer is yes to your second question as well.
Put, at very least, the code that can get called from multiple locations in a function. For example,
function stageOneCode() {
//do stuff;
}
etc.. I would recommend a function for each stage, but it's hard to make recommendations without actually seeing what's being executed in the stages.
In any event, at the end of your stage three function, simply call your stage one function.
A recursive function is helpful for this (but maybe overkill if it will always revert back to 1)
function echo_stage($stage) {
if ($a == 1) {
return "this is stage 1";
}
else if ($a == 2) {
return "this is stage 2";
}
return echo_stage(1);
}
echo echo_stage(5);
Or:
switch ($number)
{
case 2 :
echo "this is stage 2";
break;
case 1:
default:
echo "this is stage 1"
}
use switch(). you can have a "default" case as well as specific cases.
A loop is what you are searching for:
// initialize $a
$a = 1;
// the while loop will return endless
while (true);
// if you want to break for any reason use the
// break statement:
// if ($whatever) {
// break;
// }
if ($a == 1) {
echo "this is stage 1";
}
else if ($a == 2) {
echo "this is stage 2";
}
else if ($a == 3) {
$a = 1;
// continue will go back to the head
// of the loop (step 1) early:
continue;
}
// don't forget to increment $a in every loop
$a++;
}