Introducción
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 ?>
if
(PHP 4, PHP 5)
El constructor if es una de las características más importantes de muchos lenguajes, incluido PHP. Permite la ejecución condicional de fragmentos de código. PHP dispone de una estructura if que es similar a la de C:
if (expr) sentencia
Como se describe en la sección sobre
expresiones , la expresión es evaluada a su
valor booleano. Si la expresión se evalúa como TRUE,
PHP ejecutará la sentencia y si se evalúa
como FALSE la ignorará. Más información sobre qué valores evalúan
como FALSE se puede encontrar en la sección 'Convirtiendo a booleano'.
El siguiente ejemplo mostraría a es mayor que b si $a es mayor que $b:
<?php
if ($a > $b) {
echo "a es mayor que b";
}
?>
A menudo se desea tener más de una sentencia para ser ejecutada condicionalmente. Por supuesto, no hay necesidad de envolver cada sentencia con una cláusula if. En cambio, se pueden agrupar varias sentencias en un grupo de sentencias. Por ejemplo, este código mostraría a es mayor que b si $a es mayor que $b y entonces asignaría el valor de $a a $b:
<?php
if ($a > $b) {
echo "a es mayor que b";
$b = $a;
}
?>
Las sentencias if pueden anidarse dentro de otra sentencias if infinitamente, lo cual provee completa flexibilidad para la ejecución condicional de diferentes partes del programa.
add a note
User Contributed Notes
if - [19 notes]
robk ¶
2 days ago
sofwan at sofwan dot net ¶
1 year ago
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
?>
chrislabricole at yahoo dot fr ¶
4 years ago
You can do IF with this pattern :
<?php
$var = TRUE;
echo $var==TRUE ? 'TRUE' : 'FALSE'; // get TRUE
echo $var==FALSE ? 'TRUE' : 'FALSE'; // get FALSE
?>
Anonymous ¶
4 years ago
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==$string2) return FALSE and '!' will invert it into TRUE
?>
For array/float, it's the same !
grawity at gmail dot com ¶
5 years ago
re: #80305
Again useful for newbies:
if you need to compare a variable with a value, instead of doing
<?php
if ($foo == 3) bar();
?>
do
<?php
if (3 == $foo) bar();
?>
this way, if you forget a =, it will become
<?php
if (3 = $foo) bar();
?>
and PHP will report an error.
admin at leonard !spam challis dot com ¶
2 years ago
When using if statements without the curly braces, remember than only one statement will be executed as part of that condition. If you want to place multiple statements you must use curly braces, and not just put them on the same line.
<?php
if (1==0) echo "Test 1."; echo "Test 2";
?>
Whereas some people would expect nothing to be displayed, this piece of code will show: "Test 2".
john ¶
4 years ago
@henryk (and everybody):
You should put your arguments in order by *least* likely to be true. That way if php is going to be able to quit checking, it will happen sooner rather than later, and your script will run (what amounts to unnoticeably) faster.
At least, that makes the most sense to me, but I don't claim omniscience.
redrobinuk at aol dot com ¶
5 years ago
This is aimed at PHP beginners but many of us do this Ocasionally...
When writing an if statement that compares two values, remember not to use a single = statement.
eg:
<?php
if ($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...
austinderrick2 at gmail dot com ¶
3 years ago
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, $haystack)) { ...
if the returned key is actually the key 0, then the if won't be executed
===================================
contact at bsorin dot romania ¶
4 years ago
This has got the better part of my last 2 hours, so I'm putting it here, maybe it will save someone some time.
I had a
if (function1() && function2())
statement. Before returning true or false, function1() and function2() had to output some text. The trick is that, if function1() returns false, function2() is not called at all. It seems I should have known that, but it slipped my mind.
Anonymous ¶
4 years ago
Re : henryk dot kwak at gmail dot com
<?php function message($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
?>
Rudi ¶
2 years ago
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
Christian L. ¶
2 years ago
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.
techguy14 at gmail dot com ¶
2 years ago
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 || $c==6) ) {
//do that something here.
}
?>
Hope this helps!
strata_ranger at hotmail dot com ¶
4 years ago
Although most programmers are aware of this already, if for whatever reason you need to 'break' out of an if() block (which, unlike switch() is not considered a looping structure) just wrap it in an appropriate looping structure, such as a do-while(false):
<?php
do if ($foo)
{
// Do something first...
// Shall we continue with this block, or exit now?
if ($abort_if_block) break;
// Continue doing something...
} while (false);
?>
ehsan at chavoshi dot com ¶
1 year ago
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";
Donny Nyamweya ¶
2 years ago
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')
Wiseguy ¶
4 years ago
RE: chrislabricole at yahoo dot fr on 09-Aug-2008 05:53
You're referring to the ternary operator.
http://php.net/manual/en/language.operators.comparison.php
jm+phpweb at roth dot lu ¶
3 years ago
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