php break and continue statements as well as goto statements and php constants

1. Loop control break statement:

break ends the execution of the current for, while, do-while or switch structure.

Break can accept an optional numeric parameter to determine how many loops to jump out of.

<?php	

$i = 0;
while(++$i){
	switch($i){
		case 5:
		echo "quit at 5 <br>";
		break;
		case 10:
		echo "quit at 10<br>";
		break 2;  //跳出switch结构和while循环
		default:
		break;	//只跳出switch结构
	}
}
echo "$i=".$i;
<span style="font-size:18px;">?>	</span>

The execution results are as follows:

quit at 5 
quit at 10
10=10

2. Loop control continue statement:

Continue is used in the loop structure to skip the remaining code in this loop and start executing the next loop when the condition evaluates to true. continue can accept an optional The numeric parameter determines how many loops to skip to the end of the loop.

<?php 

for($i=0;$i<2;$i++)
{
	for($j=1;$j<4;$j++)
	{
		if($j==2)
		{
			continue 2;   //跳出最近的一个for循环的2次循环（j=2和j=3）
		}
	echo &#39;$i=&#39;.$i.&#39;$j=&#39;.$j."<br>";
	}
}
 ?>

Output result:

$i=0$j=1
$i=1$j=1

3. goto statement:

## PHP5.3 The above versions have increased the GOTO statement;

qi's GOTO statement has certain limitations, and can only jump in the same file and scope. Jump, that is to say, you cannot jump out of a function or class method, nor can you jump into another function. Common usage is to break out of a loop or switch, which can replace multiple levels of break.

 <?php 	
for($i=0,$j=50;$i<100;$i++)
{
	while($j--)
	{
		if($j==7) goto a;//a可任意起名
		Echo "i=$i<br>";
	}
}
a://跳转到次
echo &#39;j=17&#39;;	
 ?>	

Output result:

i=0
i=0
i=0
i=0
i=0
i=0
i=0
i=0
i=0
i=0
i=0
i=0
j=37

4, Php constant：

Constant is similar to a variable, but once a constant is defined, it cannot be changed or undefined.

PHP Constants and variables are different as follows:

## There is no dollar sign ($) in front of the constant

Constant is defined with the define() function or const, but not through an assignment statement

Constants can be defined and accessed anywhere regardless of the scope of variables(Unlike variables, constants are automatically global throughout the entire script. )

When a constant is defined, it must be assigned an initial value and once defined it cannot be redefined or undefined

The value of a constant is a scalar, which can be (string, integer, float, boolean), etc.

is valid The constant name starts with a character or an underscore, and is expressed in uppercase letters by default, separated by underscores.

Set PHP constants:

such as To set a constant, please use the define() function - it uses three parameters:

1. The first parameter defines the name of the constant

2. The second parameter defines the value of the constant

3. The optional third parameter specifies Whether constant names are case-sensitive. The default is false.

If we don’t want a certain value to change in the program, we can consider using constants, such as pi and tax rates.

<?php  

//第一种定义常量方法：

define("TAX_RATE",0.08);
echo TAX_RATE."<br>";

//第二种定义常量方法：

const TAX_RATE2 = 0.07;
echo TAX_RATE2;

?>

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