How to nest for loops in PHP

This article mainly introduces how to nest the for loop in PHP. Interested friends can refer to it. I hope it will be helpful to everyone.

The execution principle of the for loop:

The parameters of the for loop are (initial value; judgment condition; update loop variable expression). None of the three are necessary. If the three are not If it is complete, you must manually call the break command at the appropriate time to terminate the loop, otherwise the loop will continue and become an infinite loop.

The execution process is:

First determine whether the initial value meets the judgment conditions. If it meets Then start the loop. If it is not satisfied, the loop will be skipped directly. Therefore, the following loop will not be executed:

for($i=0; $i<0; $i++)

Then execute the loop body (the code wrapped in curly brackets after for)

Use the update loop variable expression to update the variable

Use the judgment condition to judge. If it is not satisfied, the loop will be terminated. If it is satisfied, the loop body will be executed again.

So the following loop will be executed 5 times.

for($i=0; $i<5; $i++)

For loop nesting:

If the for loop is nested, the inner loop will be executed first, and then the outer loop will be executed, as follows:

//外循环开始
for($i=0; $i<10; $i++）
{
    //这里是外循环的循环体
    for($j=0; $j<20; $j++)//内循环开始
    {
        //这里是内循环的循环体
     }//内循环结束
 }//外循环结束

When starting to execute the loop, first execute the loop body of the outer loop (including the inner loop), at this time $i=0; in this process, when the inner loop is executed, the inner loop starts to be executed, and $j is changed from 0 Increase to 19; after executing the inner loop 20 times, the outer loop ends, $i; at this time, $i=1, and the outer loop starts executing again.

To sum up, the outer loop body is executed 10 times in total, and the inner loop body is executed 20 times (the number of repetitions of the inner loop itself) * 10 (each outer loop executes the inner loop 20 times) = 200 times

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