What is a for loop? What is the difference between it and while loop?

The previous article introduced you to "What is a do...while loop?" And the difference with while loop? (Attached with code) 》, this article continues to introduce you to the for loop (and the difference between while loops). Don’t hesitate to come in and learn! You will definitely gain something! ! !

for loop:

The only counting type loop (higher efficiency), for for loop , it knows how many times it will loop from the beginning;

Format:

for (expression 1; expression 2; expression 3) {

Loop body (PHP statement)

}

• ##Expression 1: Represents initialization variables

• Expression 2: Indicates the condition for loop exit (conditional expression)

• Expression 3: Auto-increment and self-decrement conditions

We will explain the specific structure by code operation. The code is as follows:

<?php
     /******for 循环 唯一一个计数循环******/
     for($i = 0;$i < 10; $i++){
         echo $i;
     }
?>

The code execution result is as follows:

Code analysis: According to the format written at the beginning, first define an initial variable ($i=0), then write the condition of the loop ($i<10), and finally write the condition of self-increment and self-decrement ($i or $i--); Output the value of $i, (if $i) we can get a result of 0-9;

For the for loop, it is evolved from the while loop:

<?php
     /******for 循环 唯一一个计数循环******/
     $i = 0;
     for(;$i < 10; ){
         echo $i;
         $i++;
     }
?>

The code execution result is as follows:

About the execution format of the for loop:

Execute expression 1 and initialize the variables;

Execute expression 2 to determine whether the loop conditions are met;

If expression 2 meets the conditions for executing the loop, then execute {} The code inside (loop body)

Execute expression 3, auto-increment or decrement condition

Execute expression 2, determine whether the loop condition is met

The difference between for loop and while loop:

1: Type issue

• Counting loops only have for loops

• Boolean loops: while loop, do...while loop and foreach loop

2: Efficiency issue

The for loop is higher than the while loop, The for loop is a counting loop, while the while loop bool type loop

We know almost everything about the for loop, let’s take a few codes as examples:

<?php
     /******for 循环 唯一一个计数循环******/
     $i = 0;
     for(;$i < 10; ){
         echo $i;
         $i++;
     }
     echo &#39;<hr>&#39;;
     echo &#39;<table border="1" align="center" width="800">&#39;;
           for($tr = 0;$tr<10;$tr++){
               echo &#39;<tr>&#39;;
               for($td = 0;$td<10;$td++){
                   echo &#39;<td>&#39;.$tr.$td.&#39;</td>&#39;;
               }
               echo &#39;</tr>&#39;;
           }
           echo &#39;</table>&#39;;
?>

Code running The results are as follows:

Recommended learning: "

PHP Video Tutorial"

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