PHP Exercises: Create a new string of the characters at indexes 0,1,4,5,8,9 ... from a given string

Last update on May 28 2025 13:05:18 (UTC/GMT +8 hours)

36. New String from Specific Indexes

Write a PHP program to create a new string of the characters at indexes 0,1,4,5,8,9 ... from a given string.

Sample Solution:

PHP Code :

<?php
// Define a function that extracts substrings from a given string
function test($s)
{
    // Initialize an empty string to store the result
    $result = "";

    // Iterate through the characters of the input string with a step size of 4
    for ($i = 0; $i < strlen($s); $i = $i + 4)
    {
        // Calculate the end index of the substring
        $c = $i + 2;

        // Initialize a variable to store the substring length
        $n = 0;

        // Determine if the calculated end index is beyond the length of the string
        $z = $c > strlen($s) ? 1 : 2;

        // Update the substring length based on the condition
        $n = $n + $z;

        // Append the extracted substring to the result
        $result = $result . substr($s, $i, $n);
    }

    // Return the final result
    return $result;
}

// Test the function with different input strings
echo (test("Python"))."\n";
echo (test("JavaScript"))."\n";
echo (test("HTML"))."\n";
?>

Explanation:

Function Definition:

The test function takes a single string $s as input and extracts specific substrings based on certain conditions.

Initialize Result String:

An empty string $result is initialized to store the final result.

Iterate with Step Size of 4:

A for loop iterates through $s with a step size of 4, so i increments by 4 in each loop, meaning it processes every fourth character in the string.

Calculate Substring End Index:

For each iteration, c is set to i + 2, marking the end of a two-character substring starting at index i.

Determine Substring Length:

A variable $z determines the substring length:

If c is beyond the end of the string, $z is set to 1.
Otherwise, $z is set to 2, allowing the substring to be two characters long.

$n is updated with this value of $z, making $n the actual length of the substring to extract.

Extract and Append Substring:

The substr($s, $i, $n) function extracts a substring starting at index i with length $n, and appends it to $result.

Return the Result:

After the loop completes, $result contains the concatenated substrings extracted from $s, which the function returns.

Output:

Pyon
JaScpt
HT

Visual Presentation:

PHP Basic Algorithm Exercises: Create a new string of the characters at indexes 0,1,4,5,8,9 ... from a given string.

Flowchart:

For more Practice: Solve these Related Problems:

Write a PHP script to construct a new string using characters from specific indexes (0,1,4,5,8,9, etc.) of the input string.
Write a PHP function to extract characters from an array of specified positions and concatenate them into a result.
Write a PHP program to use a mapping of indexes to rebuild a string containing only selected characters.
Write a PHP script to check the length and then assemble a new string based on fixed index positions from the original.

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