How to traverse an array in php and only take the first three elements

php method to traverse an array and only take the first three elements: 1. Use the for statement to loop through the array, the syntax is "for($i=0; $i2 ){break;}else{echo $array[$i]."
";}". ($array);>

The operating environment of this tutorial: windows7 system, PHP8 version, DELL G3 computer

In php , you can use the for statement and if statement to traverse the array and only take the first three elements.

• The for statement is used to traverse the array

• The if statement is used to limit the number of traversals and obtain the first three elements

Detailed steps:

Step 1. Use the for statement to loop through the array

For syntax for looping through the array The format is as follows:

for ($i=0; $i< 数组长度; $i++) {
    //循环体语句块;  
}

Let’s take a look at the code example below:

<?php
header("Content-type:text/html;charset=utf-8");
$array= array(2,"数学","梨子",3.14,"榴莲",12);
for ($i=0; $i < count($array); $i++) { 
    echo $array[$i] . "<br/>";
} 
?>

At this time, all elements will be obtained, and restrictions need to be added to the loop body. .

Step 2: In the loop body, use the if statement to determine whether the variable $i is greater than 2. If it is greater than 2, use the break statement to jump out of the loop. If it is not greater, continue to output elements

• If it is greater, it means that the array has been traversed 3 times and the first three elements have been obtained. At this time, you need to use the break statement to jump out of the loop

• If it is not greater, the first three elements have not been obtained and the output continues.

<?php
header("Content-type:text/html;charset=utf-8");
$array= array(2,"数学","梨子",3.14,"榴莲",12);
for ($i=0; $i < count($array); $i++) {
	if($i>2){
		break;
	}else{
		echo $array[$i] . "<br/>";
	}
} 
?>

ok, you can see that the first three elements are output.

Extended knowledge: for loop statement

The for loop will pre-define the variable that controls the number of loops in the for statement, so the for loop statement Able to perform loop operations according to a known number of loops, suitable for situations where the number of times the script needs to be run is clearly known.

The syntax format of the for loop is as follows:

for (初始化语句; 循环条件; 变量更新--自增或自减) {
    语句块;   
}

The for loop statement can be disassembled into 4 parts: three of the () Expressions and "statement blocks" in {}, let's analyze them below.

Statement analysis:

• #Initialization statement (expression 1): mainly initializes a variable value, used to set a counter , which is the value at the beginning of the loop; this statement is only executed during the first loop and will not be executed again in the future.

• Loop condition (expression 2): Restriction condition for loop execution, used to control whether to execute the code in the loop body; if the condition is TRUE, the loop continues, if the condition is FALSE , the loop ends and exits the loop immediately.
  

• Variable update (expression 3): an expression with an increment or decrement operation. Every time the loop is executed, the value of the counter is immediately modified so that the loop The conditions gradually become "untenable".
  

• Statement block: Several codes that need to be executed when the condition is judged to be true.
  

Is the above description a bit convoluted? Let’s take a look at the execution flow chart of the for loop statement to understand the execution of the for loop more intuitively. Process:

# Now that we understand the execution process of the for loop, let’s do the actual operation and do a small question to see if we have mastered it!

Training question:

Calculate the sum of adding from 1 to 100

<?php
$sum=0;
for($i=1; $i<=100; $i++){
    $sum+=$i;
}
echo &#39;1 + 2 + 3 +...+ 99 + 100 = &#39;. $sum;
?>

Output:

1 + 2 + 3 +...+ 99 + 100 = 5050

Let’s change it, since You can find the sum of 1 added to 100, or you can find the product of 1 multiplied by 100 (the factorial of 100)

<?php
$sum=1;
for($i=1; $i<=100; $i++){
    $sum*=$i;
}
echo &#39;1 * 2 * 3 *...* 99 * 100 = &#39;. $sum;
?>

Output:

1 * 2 * 3 *...* 99 * 100 = 9.3326215443944E+157

Note: Because nothing is multiplied by 0 It is 0, so the initial value of the $sum variable here cannot be 0, but 1.

Recommended learning: "PHP Video Tutorial"

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