Thats the code:
switch (true)
{
case (isset($_REQUEST['a']) && is_numeric($_REQUEST['a']) && ($_REQUEST['a'] > 0)):
case (isset($_REQUEST['b']) && is_string($_REQUEST['b']) && in_array($_REQUEST['b'], $barray)):
case (isset($_REQUEST['c']) && is_numeric($_REQUEST['c']) && ($_REQUEST['c'] > 0) && ($_REQUEST['c'] <= $cbase)):
try { echo "Foo"; }
catch(Exception $e) { echo $e->getMessage(); }
break;
default:
echo "Bar"; break;
}
I'm wondering if these are allowed for use in switch cases?
Very soon I must use switch because of many comparisons and willing to try it. In this case 3rd case gives me always correct output, even when $_REQUEST['c'] is bigger than $cbase, while should fall to default :|
Yes this is valid. Using switch(TRUE) enables you to have strict comparisons in a switch statement. check this examples:
Not typesafe:
$a = '1';
switch($a) {
case 1 :
// do something (will get executed)
break;
case '1' :
// do something:
break;
}
Better:
$a = '1';
switch(TRUE) {
case $a === 1 :
// do something; (will not get executed)
break;
case $a === '1' :
// .. do something;
break;
}
Also this usage allows for more complex case statements, like this:
switch(TRUE) {
case strpos($input, 'a') === 0 :
// do something
break;
case strpos($input, 'b') === 0 :
// do something
break;
}
Related
I have this simple function to convert the number of comments of an user to types of members.
function checkMemberN($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.
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
For the following php program with a switch statement, why '' give me $vSS=2 instead of =1?
Quite strange to me. I am using PHP 5.5.9.
I can add case '': to resolve the problem, but I am curious why PHP give $vSS=2 instead of
$vSS=1. Is it normal or a bug?
<?php
R(15); // 1 ok
R(''); // why give me 2
R(40); // 2 ok
R(70); // 3 ok
#
function R($SS){
switch($SS){
case $SS<=20: $vSS=1;break;
case ($SS>20 and $SS<=49.9): $vSS=2; // why here?
if($SS == '') echo "DEBUG: SS is a null string.<br>\n";
break;
case ($SS<=100 and $SS>49.9): $vSS=3; break;
default:$vSS=0 ;
}
echo "DEBUG:(SS/vSS) $SS:$vSS\n";
}
?>
------ RESULT
DEBUG:(SS/vSS) 15:1
DEBUG: SS is a null string.<br>
DEBUG:(SS/vSS) :2
DEBUG:(SS/vSS) 40:2
DEBUG:(SS/vSS) 70:3
You don't understand how switch works. It compares the value in switch($SS) with each of the case values, it doesn't just test each case. So
switch ($SS) {
case $SS<=20:
is similar to:
if ($SS == ($SS<=20))
The reason the second case is being executed is because ($SS > 20 && $SS <= 49.9) is false, and false is considered equal to zero or an empty string.
You shouldn't use switch for what you're doing, you should use if/then/elseif/else:
if ($SS <= 20) {
$vSS = 1;
} elseif ($SS <= 49.9) {
$vSS = 2;
} else {
$vSS = 0;
}
#Barmar is right, expression in case() is compared to switch(something_here) but you don't have to cahnge your all your code to if/elsif/elsif/.../... logic. Just change switch() statement to true
switch(true) { // <-- this part only
case $SS<=20:
$vSS=1;
break;
case ($SS>20 and $SS<=49.9):
$vSS=2; // why here?
// must not be here
// if($SS == '') echo "DEBUG: SS is a null string.<br>\n";
break;
case ($SS<=100 and $SS>49.9):
$vSS=3;
break;
case $SS=='': // you can check it here
echo "DEBUG: SS is a null string.<br>\n";
break;
default:
$vSS=0 ;
}
I was wondering what the quickest way would be to do something like the following:
if ($var == 1) {
// 1
}
if ($var == 2) {
// 2
}
if ($var == 3) {
// 3
}
etc, but then at the end having something like:
if ($var != 1 or 2 or 3) {
//Not a number
}
I was thinking about having an if(in_array(...)) statement at the end, but wanted to know your thoughts.
I would do this with a switch
switch ($var) {
case 0:
echo "var equals 0";
break;
case 1:
echo "var equals 1";
break;
case 2:
echo "var equals 2";
break;
default:
echo "var is not 0 1 or 2"
}
Also if you miss out a break statement then you can easily do a case when $var == 1 || $var == 2, read more
If all you want to know is whether "$var" is in your set {1, 2, 3}, then in_array is fine.
Otherwise, if you want to know which (if any) value you've got, then I'd do this:
if ($var == 1) {
// 1
}
else if ($var == 2) {
// 2
}
else if ($var == 3) {
// 3
}
else {
}
Note the "else if" to save you from re-checking what you already know.
Note, too, that PHP 4 and 5 also have a "switch" case/block:
switch ($i) {
case 1:
// 1
break;
case 2:
// 2
break;
case 3:
// 3
break;
default:
...
}
Or use a switch case, this better to read for much cases:
switch($var) {
case 1: /*1*/ break;
case 2: /*2*/ break;
case 3: /*3*/ break;
default: /*not 1 not 2 not 3*/
}
Use if/else if/else, with which you can decide whether strict or loose comparisons are appropriate.
With switch, it's always loose comparisons, which is why I prefer the if statement, since it makes it explicit what mode has been chosen.
if ($var === 1) {
// 1
}
else if ($var === 2) {
// 2
}
else if ($var === 3) {
// 3
}
else {
//neither 1, 2 nor 3
}
I have an array of conditions :
$arrConditions = array ('>=2', '==1', '<=10');
...which I want to be able to use in an if...statement.
IE.
if (5 $arrConditions[0])
{
...do something
}
...which would be the same as :
if (5 >= 2)
{
...do something
}
Any help?
Thanks
Such a requirement is a sure sign of a bad design.
Most likely you can do that another, more usual way.
Nevertheless, never use eval for such things.
At least store each operator in pairs - an operator and operand.
$arrConditions = array (
array('>=',2),
array('==',1),
array('<=',10),
);
and then use switch:
list ($operator,$operand) = $arrConditions[0];
switch($operator) {
case '==':
$result = ($input == $operand);
break;
case '>=':
$result = ($input >= $operand);
break;
// and so on
}
But again - most likely you can solve it another, much easier way.
What about this ?
<?php
$arrConditions = array('==2', '==9', '==5', '==1', '==10', '==6', '==7');
$count = 0;
$myval = 0;
foreach ($arrConditions as $cond) {
$str = "if(5 $cond) { return $count;}";
$evalval = eval($str);
if (!empty($evalval)) {
$myval = $count;
}
$count++;
}
switch ($myval) {
case 0: echo '==2 satisfied';
break;
case 1: echo '==9 satisfied';
break;
case 2: echo '==5 satisfied';
break;
case 3: echo '==1 satisfied';
break;
case 4: echo '==10 satisfied';
break;
default : echo 'No condition satisfied';
}
?>