<?php
$var = null ?? true;
var_dump($var); //bool(true)
$var = 0 ?? true;
var_dump($var); //int(0)
$var = false ?? true;
var_dump($var); //bool(false)
$var = 'PHP' ?? true;
var_dump($var); //string(3) "PHP"
?>
(PHP 4, PHP 5, PHP 7, PHP 8)
if 结构是很多语言包括 PHP
在内最重要的特性之一，它允许按照条件执行代码片段。PHP 的
if 结构和 C 语言相似：
<?php if (expr) statement ?>
如同在表达式一章中定义的，expr
按照布尔求值。如果 expr
的值为 true，PHP 将执行 statement，如果值为
false ——将忽略 statement。有关哪些值被视为
false 的更多信息参见转换为布尔值一节。
如果 $a 大于 $b，则以下例子将显示 a is bigger than b：
<?php
if ($a > $b)
echo "a is bigger than b";
?>
经常需要按照条件执行不止一条语句，当然并不需要给每条语句都加上一个
if 子句。可以将这些语句放入语句组中。例如，如果
$a 大于 $b，以下代码将显示
a is bigger than b 并且将
$a 的值赋给 $b：
<?php
if ($a > $b) {
echo "a is bigger than b";
$b = $a;
}
?>
if 语句可以无限层地嵌套在其它
if 语句中，这给程序的不同部分的条件执行提供了充分的弹性。
<?php
$var = null ?? true;
var_dump($var); //bool(true)
$var = 0 ?? true;
var_dump($var); //int(0)
$var = false ?? true;
var_dump($var); //bool(false)
$var = 'PHP' ?? true;
var_dump($var); //string(3) "PHP"
?>
<?php
//Print the day or night message by if command
$t = date("H");
if ($t < "20") {
echo "Have a good day !";
if ($t > "20") {
echo "Have a good Night!";
}
}
?>
Normal if example;
if($value["cargostatus"]==0):
echo 'In the Procurement Process';
elseif ($value["cargostatus"]==1):
echo 'In packaging';
elseif ($value["cargostatus"]==2):
echo 'In cargo';
else:
echo 'not specified';
endif;
Multiple comparison operator example in a single line;
($value["cargostatus"] == "0") ? 'In the Procurement Process' : (($value["cargostatus"] == "1") ? 'In packaging
' : (($value["cargostatus"] == "2") ? 'In cargo' : 'not specified'))
What should not be forgotten;
After the first query, a parenthesis will be added to the end of each comparison.
//to use if condition and html together
<?php if(condition) : ?>
// just html code
<?php elseif( condition ): ?>
// just html code
<?php else: ?>
// just html code
<?php endif?>
You can use this syntax :
if (condition):
// your code
else if:
// your code
else:
// Your code
endif ;
Any variables defined inside the if block will be available outside the block. Remember that the if doesn't have its own scope.
<?php
$bool = true;
if ($bool) {
$hi = 'Hello to all people!';
}
echo $hi;
?>
It will print 'Hello to all people!'
On the other hand, this will have no output:
<?php
if (false) {
$hi = 'Hello to all people!';
}
echo $hi;
?>
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 ?>
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')
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 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 || $c==6) ) {
//do that something here.
}
?>
Hope this helps!
re: #80305
Again useful for newbies:
if you need to compare a variable with a value, instead of doing
<?php
if ($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.