Notes on the basic syntax structure of PHP loop statements

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Notes on the basic syntax structure of PHP loop statements_PHP tutorial

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Jul 13, 2016 am 10:50 AM

for foreach php exist Basic cycle notes statement Grammatical structures

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

复制代码

//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

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