PHP function Exercises: Reverse a string

Last update on December 20 2024 10:25:10 (UTC/GMT +8 hours)

Write a PHP function to reverse a string.

Visual Presentation:

Sample Salution:

PHP Code:

<?php
// Function to reverse a string recursively
function reverse_string($str1)
{
    // Get the length of the string
    $n = strlen($str1);
    
    // Base case: if the string has only one character, return the string itself
    if ($n == 1)
    {
        return $str1;
    }
    else
    {
        // Decrement the length of the string
        $n--;
        
        // Recursively reverse the substring starting from the second character
        // and concatenate the first character to it
        return reverse_string(substr($str1, 1, $n)) . substr($str1, 0, 1);
    }
}

// Call the reverse_string function with the argument '1234' and print the result
print_r(reverse_string('1234') . "\n");
?>

Output:

4321

Explanation:

In the exercise above,

• The function "reverse_string()" takes a single parameter '$str1', representing the input string to be reversed.
• It calculates the length of the input string using 'strlen($str1)' and stores it in the variable '$n'.
• If the length of the string is 1, it means the string is already reversed, so it returns the string itself.
• Otherwise, it decrements the length of the string by 1 ($n--), and then recursively reverses the substring starting from the second character using 'substr($str1, 1, $n)', and concatenates the first character using 'substr($str1, 0, 1)'.
• This recursive process continues until the base case (string length equals 1) is reached, and the reversed string is gradually built up.
• Finally, the function is called with the argument '1234', and the reversed string is printed using "print_r()" function.

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