Notes on the basic syntax structure of PHP loop statements

There are many loop statements in PHP, such as: for, foreach, while, do while, goto statements. Let me briefly introduce the usage of these loop statement structures.

for loop control

for(initial value of loop; condition of loop; step size){

//Execute statement;

}

Example

The code is as follows

Copy code

代码如下	复制代码
FOR ($i = 0; $i <= 2; $i++) { print "value is now " . $i . " "; }

FOR ($i = 0; $i <= 2; $i++)

{

print "value is now " . $i . "
";

}

Output value

value is now 0

value is now 1

value is now 2

In the first loop, $i=0, which means that the expression, ($i<= 2), is true. Therefore, when the print statement is executed, $i is incremented by 1 and becomes 1.

In the second loop, $ = 1, which means that the expression, ($i<= 2), is true. Therefore, when the print statement is executed, $i is incremented by 1 and becomes 2.

In the third iteration, $i= 2, which means that the expression, ($i<= 2), is true. Therefore, when the print statement is executed, $i is incremented and becomes 1 3. In the fourth iteration, $i= 3, which means the expression, ($i<= 2), is false. Therefore, PHP does not execute the loop and does not execute the print statement.

while loop

The basic grammatical structure is

while(loop condition){

//Execute statement;

//The loop condition value changes. If it is not added, it will become an infinite loop

代码如下

复制代码

"; $a++; }?>

}

Example

The code is as follows	Copy code
"; $a++; }?>

Let’s take a simple example and you’ll understand it at a glance. The following example uses a while loop statement. It means that when the variable $a is less than or equal to 5, a loop is executed. The loop executes two statements. One is to output the value of $a, and the other is to give $a Add 1 to the value, and stop looping until $a is less than or equal to 5 and is FALSE, that is, $a > 5.

do..while loop control

Basic grammatical structure

do{

//Execute statement;

//The loop condition value changes. If it is not added, it will become an infinite loop

代码如下	复制代码
"; }while ($i<5);?>

}while(loop condition); Example The example is as follows. In this example, a loop is first executed, that is, $i is increased by 1, and then the value of $i is output. After executing the first loop, the condition $i < 5 is checked. If the condition is met, then Execute a loop until $i < 5 is FALSE.

The code is as follows	Copy code
"; }while ($i<5);?>

Loop related statements-break

Basic concept: Indicates the end of the current for, while, do..while, switch, process. You can give a number to indicate which layer to exit to.

1. The break statement will jump out to level 1 by default

2. The number after the break statement cannot exceed the actual number of loop levels that can be jumped out, otherwise, a fatal error will be reported

Loop-related statements-continue

Basic concept: continue is used to end the remaining code of this loop and start a new loop from scratch (if the condition is true, continue execution), continue can also be followed by a number to indicate the number of loops to restart from

goto statement

Basic concept: Through the goto statement, we can jump the program to a specified place for execution.

goto tag;

Tag:

Statement;

Quick Start Case:

3. When a constant is defined, it needs to be assigned an initial value.

The code is as follows

代码如下

复制代码

goto a;

echo 'aa';

echo 'bb';

Copy code

goto a;

echo 'aa';

echo 'bb';

Constant in php

Description:

The so-called constants, we can understand that achievements are special variables: reflected in

1. You don’t need $ before defining a constant

2. Once a constant is defined, its value cannot be modified

代码如下

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//第一种方法

define("TAX_RATE",0.08);
echo TAX_RATE;

//第二种方法(php5.3)

const TAX_RATE2=0.1;
echo '-'.TAX_RATE2;

4. Constants can be defined or const

5. The name of the constant, we generally say it is all capital letters, and then separated by underscores

Related labels：

for foreach php exist Basic cycle notes statement Grammatical structures

source：php.cn

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