How to loop through the first few elements of a php array

Implementation steps: 1. Define a variable and assign it to 0, which is used to control the number of loop elements. The syntax is "$con=0;"; 2. Use the foreach statement to loop through the array, the syntax is "foreach($ arr as $k=>$v){//loop body;}"; 3. In the loop body, each loop traverses an element, and sets the variable "$con" to increase by 1. When the value of the variable "$con" When it is N, just use the break statement to jump out of the loop, the syntax is "$con ;if($con==N){break;}".

The operating environment of this tutorial: windows7 system, PHP version 8.1, DELL G3 computer

In the php array, you can use the foreach statement and break statement to loop through the first N elements.

Implementation steps:

Step 1: Define a variable and assign it a value of 0, which is used to control the number of loop traversals (number of elements) number).

$con=0;

Step 2: Use the foreach statement to loop through the array

foreach is a statement specially designed for traversing arrays, and is a commonly used method when traversing arrays. It provides great convenience in traversing arrays

The foreach statement traverses arrays regardless of array subscripts, and can be used for discontinuous index arrays and associative arrays with strings as subscripts.

This statement has two syntax formats:

• Syntax format 1:

##

foreach ($array as $value){
    //循环体语句块;
}

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• Syntax format 2:

foreach ($array as $key => $value){
    //循环体语句块;
}

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Step 3: In the loop body, set the variable $con to increment by 1. When the value of the variable $con is N, use the break statementJump out of the loop

• Each time the loop traverses an element, add 1 to the value of variable $con

• Then determine whether the value of variable $con is N, if so Then use the break statement to jump out of the loop

• If not, continue to traverse the elements

$con++;
if($con==N){ //循环遍历前N个元素
	break;
}

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Complete sample code: Loop through the first 5 elements

<?php
header("Content-type:text/html;charset=utf-8"); 
$arr=[1,2,3,4,5,6,7,8,9];
var_dump($arr);
$con=0;
foreach($arr as $k=>$v){
	$res[$k]=$v;
$con++;
if($con==5){ //循环遍历前5个元素
	break;
}
}
echo "循环遍历前5个元素:";
var_dump($res);
?>

Expand knowledge: Break out of the loop statement break and continue

1. Use the continue statement

Example 1: Output all even numbers between 1 and 10 (even numbers can be divisible by 2)

<?php
    for ($i = 1; $i <= 10; $i++) {
        if($i % 2 != 0) {
            continue;
        }
        echo $i.&#39; <br>&#39;;
    }
?>

• for ($i = 1; $i <= 10; $i ){}The statement can loop to get all numbers between 1~10

• if($i % 2 != 0) statement is used to judge whether the value of $i can be divided evenly by 2. If it cannot be divided evenly, the value in () is true, the continue; statement will be executed.

• In the loop body, use the

  if($i % 2 != 0) statement to make a judgment. If the value of $i can be divided by 2, use "echo $i" output; if the value of $i cannot be divided evenly by 2, the continue; statement will be triggered, jump out of this loop (without output), and execute the next loop.
  

2. Use break statement

Use the code in Example 1 above and replace continue; with break;. What will be output?

<?php
    for ($i = 1; $i <= 10; $i++) {
        if($i % 2 != 0) {
            break;
        }
        echo $i.&#39; <br>&#39;;
    }
?>

Nothing is output. Why is this happening? Let’s analyze it:

$i=1, is 1 less than 10? Of course, then start executing the if($i % 2 != 0) statement in the loop body;

() is true, then the "break;" statement in the if is executed, jumping out of the entire loop directly, and there is no chance to execute "echo $i.' '" statement.

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