easy way to execute conditional html / javascript / css / other language code with php if else:
<?php if (condition): ?>
html code to run if condition is true
<?php else: ?>
html code to run if condition is false
<?php endif ?>
(PHP 4, PHP 5, PHP 7)
The if construct is one of the most important features of many languages, PHP included. It allows for conditional execution of code fragments. PHP features an if structure that is similar to that of C:
if (expr) statement
As described in the section about
expressions, expression is evaluated to its
Boolean value. If expression evaluates to TRUE,
PHP will execute statement, and if it evaluates
to FALSE - it'll ignore it. More information about what values evaluate
to FALSE can be found in the 'Converting to boolean'
section.
The following example would display a is bigger than b if $a is bigger than $b:
<?php
if ($a > $b)
echo "a is bigger than b";
?>
Often you'd want to have more than one statement to be executed conditionally. Of course, there's no need to wrap each statement with an if clause. Instead, you can group several statements into a statement group. For example, this code would display a is bigger than b if $a is bigger than $b, and would then assign the value of $a into $b:
<?php
if ($a > $b) {
echo "a is bigger than b";
$b = $a;
}
?>
If statements can be nested infinitely within other if statements, which provides you with complete flexibility for conditional execution of the various parts of your program.
easy way to execute conditional html / javascript / css / other language code with php if else:
<?php if (condition): ?>
html code to run if condition is true
<?php else: ?>
html code to run if condition is false
<?php endif ?>
An other way for controls is the ternary operator (see Comparison Operators) that can be used as follows:
<?php
$v = 1;
$r = (1 == $v) ? 'Yes' : 'No'; // $r is set to 'Yes'
$r = (3 == $v) ? 'Yes' : 'No'; // $r is set to 'No'
echo (1 == $v) ? 'Yes' : 'No'; // 'Yes' will be printed
// and since PHP 5.3
$v = 'My Value';
$r = ($v) ?: 'No Value'; // $r is set to 'My Value' because $v is evaluated to TRUE
$v = '';
echo ($v) ?: 'No Value'; // 'No Value' will be printed because $v is evaluated to FALSE
?>
Parentheses can be left out in all examples above.
You can also check alphabet characters like this
<?php
// Alphabetical Comparison
$a="brian";
$b="zebra";
if ($a < $b){
echo $a." is before ".$b." in the alphabet";
}
else{
echo $a." is after ".$b." in the alphabet";
}
// Result : brian is before zebra in the alphabet
?>
you can use 'true/false/null' if you don't have an 'else' condition. it fit with 'for' statement.
eg.
for ($x=0; $x<10; $x++,($x==3) ? die("it's 3!") : false);
In addition to the traditional syntax for if (condition) action;
I am fond of the ternary operator that does the same thing, but with fewer words and code to type:
(condition ? action_if_true: action_if_false;)
example
(x > y? 'Passed the test' : 'Failed the test')
You can do IF with this pattern :
<?php
$var = TRUE;
echo $var==TRUE ? 'TRUE' : 'FALSE'; // get TRUE
echo $var==FALSE ? 'TRUE' : 'FALSE'; // get FALSE
?>
@henryk (and everybody):
You should put your arguments in order by *least* likely to be true. That way if php is going to be able to quit checking, it will happen sooner rather than later, and your script will run (what amounts to unnoticeably) faster.
At least, that makes the most sense to me, but I don't claim omniscience.
As an added note to the guy below, in such a case, use the !== operator like this.
$nkey = array_search($needle, $haystack);
if ($nkey !== false) { ...
The !== and the === compare the "types". So, with this type of comparision, 0 is not the same as the FALSE returned by the array_search array when it can not find a match. :)
Quoted Text:
===================================
Be careful with stuff like
if ($nkey = array_search($needle, $haystack)) { ...
if the returned key is actually the key 0, then the if won't be executed
===================================
re: #80305
Again useful for newbies:
if you need to compare a variable with a value, instead of doing
<?php
if ($foo == 3) bar();
?>
do
<?php
if (3 == $foo) bar();
?>
this way, if you forget a =, it will become
<?php
if (3 = $foo) bar();
?>
and PHP will report an error.
you want créate IF in for with multi var :
(#) ? A : B; or ((#) ? A : B);
but is possibli this
((#) ? A.B.C.D : E.F.G.H);
exemple
(( $A>=$B ) ? ($A++) . ($B--) : ($A--) . ($B++) );
echo $A, PHP_EOL;
echo $B, PHP_EOL;
exemple :
<?php
For( $A=0 , $B=10 , $C=50 ; $A<=$C ; $A++, (( $A>=$B ) ? ($A++) . ($B--) : ($A--) . ($B++) ) ) {
echo $A, PHP_EOL;
echo $B, PHP_EOL;
echo $C, PHP_EOL;
}
?>
You can have 'nested' if statements withing a single if statement, using additional parenthesis.
For example, instead of having:
<?php
if( $a == 1 || $a == 2 ) {
if( $b == 3 || $b == 4 ) {
if( $c == 5 || $ d == 6 ) {
//Do something here.
}
}
}
?>
You could just simply do this:
<?php
if( ($a==1 || $a==2) && ($b==3 || $b==4) && ($c==5 || $c==6) ) {
//do that something here.
}
?>
Hope this helps!
If you need to do something when a function return FALSE and nothing when it return TRUE you can do it like that :
<?php
function call()
{
return FALSE;
}
if(call()==TRUE) // or if(call())
{
// nothing to do
}
else
{
// do something here
}
?>
You can also write it like this :
<?php
if(!call()==TRUE) // or if(!call())
{
// do something here
}
// here '!' will invert 'FALSE' (from call()) into 'TRUE'
?>
/!\ WARNING /!\
The '!' only work with booleans !
Check http://fr.php.net/manual/en/language.types.boolean.php to know if you can use '!'
If you want to compare two strings and use '!' be careful how you use it !!!!
<?php
$string1 = "cake";
$string2 = "foo";
if(!$string1==$string2)
{
echo "cake is a lie";
}
//this will ALWAYS fail without exception because '!' is applied to $string1 and not to '$string1==$string2'
//to work, you have to do like this
if(!($string1==$string2))
{
echo "cake is a lie";
}
//it will display 'cake is a lie' because ($string1==$string2) return FALSE and '!' will invert it into TRUE
?>
For array/float, it's the same !
You can use a simple if and echo structure :
$i==1 and print "i is 1"
is identical with
if ($i ==1)
echo "i is 1";
$det = $b*$b-4*$a*$c;
if ($det <0)
{
echo "bubb $a⋅x² + $b⋅x + $c = 0 does not have an answer.";
}
elseif ($det ==0)
{
$loesung = round(-$b/(2*$a),2);
echo "blubb $a⋅x² + $b⋅x + $c = 0 does not have an answer.";
}
elseif ($det > 0)
{
$loesung1 = round((-$b+sqrt($det))/(2*$a),2);
$loesung2 = round((-$b-sqrt($det))/(2*$a),2);
echo "blubb $a⋅x² + $b⋅x + $c = 0 does have an answer $loesung1 and $loesung2.";
}
It seems that only numbers can be compared between them but actually an alphabet can be compare too. For example :
<?php
// Number comparison
$a="C";
$b="X";
if ($a<$b)
{
echo $a."is smaller than".$b;
}
// Result : C is smaller than X
?>
Although most programmers are aware of this already, if for whatever reason you need to 'break' out of an if() block (which, unlike switch() is not considered a looping structure) just wrap it in an appropriate looping structure, such as a do-while(false):
<?php
do if ($foo)
{
// Do something first...
// Shall we continue with this block, or exit now?
if ($abort_if_block) break;
// Continue doing something...
} while (false);
?>
When using if statements without the curly braces, remember than only one statement will be executed as part of that condition. If you want to place multiple statements you must use curly braces, and not just put them on the same line.
<?php
if (1==0) echo "Test 1."; echo "Test 2";
?>
Whereas some people would expect nothing to be displayed, this piece of code will show: "Test 2".
This has got the better part of my last 2 hours, so I'm putting it here, maybe it will save someone some time.
I had a
if (function1() && function2())
statement. Before returning true or false, function1() and function2() had to output some text. The trick is that, if function1() returns false, function2() is not called at all. It seems I should have known that, but it slipped my mind.
Re : henryk dot kwak at gmail dot com
<?php function message($m)
{
echo "$m <br />\r";
return true;
}
$k=false;
if (message("first")&& $k && message("second")){;}
// will show
//first
class
$k=true;
if (message("first")&& $k && message("second")){;}
// will show
//first
//second
?>
This is aimed at PHP beginners but many of us do this Ocasionally...
When writing an if statement that compares two values, remember not to use a single = statement.
eg:
<?php
if ($a = $b)
{
print("something");
}
?>
This will assign $a the value $b and output the statement.
To see if $a is exactly equal to $b (value not type) It should be:
<?php
if ($a == $b)
{
print("something");
}
?>
Simple stuff but it can cause havok deep in classes/functions etc...
Why can't we quit an if block?
What's funny is that PHP has "goto", allows to include() stuff (from which you can "return"), etc.etc., but you can't just quit an if-block but must resort to hacks like
<?php
if($bla) { do{
$bla = get_bla();
if(empty($bla)) break;
...
} while(false); }
?>
<div id="carousel-example-generic" class="carousel slide" data-ride="carousel">
<div class="carousel-inner" role="listbox">
<?php
$i = 0;
while(($row = mysql_fetch_array($query2))) {
if ( $i == 0 ) { ?>
<div class="item active">
<img src="images/<?php echo $row['image'] ?>" alt="<?php echo $row['title'] ?>">
</div>
<?php
$i++ ;
}
else { ?>
<div class="item">
<img src="images/<?php echo $row['image'] ?>" alt="<?php echo $row['title'] ?>">
</div>
<?php } ?>
<?php } ?>
</div>
</div>
If you intend only a single line (one-way) conditional script, you can do the following:
empty($user) || $user->save();
if $user variable is empty, it will not execute $user->save(). Otherwise it will perform saving operation. In other words/form of expression, it can be expressed like this:
if(!empty($user))
$user->save();
Note that safe type checking (using === and !== instead of == and !=) is in general somewhat faster. When you're using non-safe type checking and a conversion is really needed for checking, safe type checking is considerably faster.
===================================
Test (100,000,000 runs):
<?php
$start = microtime(true);
for($i = 0; $i < 100000000; $i++)
if(5 == 10) {}
$end = microtime(true);
echo "1: ".($end - $start)."<br />\n";
unset($start, $end);
$start = microtime(true);
for($i = 0; $i < 100000000; $i++)
if('foobar' == 10) {}
$end = microtime(true);
echo "2: ".($end - $start)."<br />\n";
unset($start, $end);
$start = microtime(true);
for($i = 0; $i < 100000000; $i++)
if(5 === 10) {}
$end = microtime(true);
echo "3: ".($end - $start)."<br />\n";
unset($start, $end);
$start = microtime(true);
for($i = 0; $i < 100000000; $i++)
if('foobar' === 10) {}
$end = microtime(true);
echo "4: ".($end - $start)."<br />\n";
unset($start, $end);
?>
===================================
Result (depending on hardware configuration):
1: 16.779544115067
2: 21.305675029755
3: 16.345532178879
4: 15.991420030594
$det = $b*$b-4*$a*$c;
if ($det <0)
{
echo "Die Gleichung $a⋅x² + $b⋅x + $c = 0 hat keine Lösung.";
}
elseif ($det ==0)
{
$loesung = round(-$b/(2*$a),2);
echo "Die Gleichung $a⋅x² + $b⋅x + $c = 0 hat die Lösung $loesung.";
}
elseif ($det > 0)
{
$loesung1 = round((-$b+sqrt($det))/(2*$a),2);
$loesung2 = round((-$b-sqrt($det))/(2*$a),2);
echo "Die Gleichung $a⋅x² + $b⋅x + $c = 0 hat die Lösungen $loesung1 und $loesung2.";
}