How to reverse array using PHP without resorting to functions

PHP is a scripting language widely used in Web programming. Its powerful array function can help us process data quickly. Among them, array reversal is a basic operation. This article will introduce how to use PHP array reversal without the help of functions.

1. Understanding array reversal

In PHP, array reversal refers to reversing the order of the original array, that is, changing the last element in the array to the first elements, the second element becomes the penultimate element, and so on. For example, after inverting the array $myArray = array(1,2,3,4,5);, the result is $myArray = array(5,4,3,2,1);

2. Use a for loop to reverse an array

The for loop structure in PHP is a very basic statement that is suitable for looping through an array and operating on it in each loop. Below shows how to reverse an array using a for loop.

$myArray = array(1,2,3,4,5);
$arraySize = count($myArray);
for($i = 0; $i < $arraySize / 2; $i++){
    $temp = $myArray[$i];
    $myArray[$i] = $myArray[$arraySize - $i - 1];
    $myArray[$arraySize - $i - 1] = $temp;
}
print_r($myArray);

The above code reverses the array $myArray and uses the print_r function to output the reversed array.

Code analysis:

• We first create an array named $myArray and use the count function to get its size.
• Next, we use a for loop to traverse the array. Note that since we want to exchange the corresponding elements in the array, we only need to traverse the first half of the array and use the temporary variable $temp to store the intermediate results.
• In each iteration of the for loop, we need to swap the elements in the first half of the original array with the elements in the second half. For the i-th element, it corresponds to the ($arraySize - $i - 1)-th element.
• Finally, we use the print_r function to output the reversed array.

3. Use a while loop to reverse an array

In addition to the for loop, you can also use a while loop to reverse an array. Below shows how to reverse an array using a while loop.

$myArray = array(1,2,3,4,5);
$arraySize = count($myArray);
$i = 0;
while ($i < $arraySize / 2) {
    $temp = $myArray[$i];
    $myArray[$i] = $myArray[$arraySize - $i - 1];
    $myArray[$arraySize - $i - 1] = $temp;
    $i++;
}
print_r($myArray);

The above code is basically the same as the previous example, except that a while loop is used instead of a for loop.

Code analysis:

• We first declare a counter named $i and set it to 0. Next, use a while loop to iterate through the array. On each iteration, increment the counter by 1.
• The code in the loop body is almost the same as the code in the for loop. The only difference is that in the while loop you need to manually increment the value of $i in order to process the next element in the next loop iteration.

4. Summary

This article introduces how to use PHP array reversal without the help of functions. By using for loops and while loops, we can do this quickly and concisely. It should be noted that no matter which loop structure is used, reversing the array requires element exchange, so temporary variables need to be used to temporarily store the intermediate results during the implementation process. Finally, the reversed array is output through the print_r function so that we can verify it.

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