PHP Exercises: Create a new string where 'if' is added to the front of a given string

Last update on May 28 2025 09:28:53 (UTC/GMT +8 hours)

5. Prepend 'if' to String if Missing

Write a PHP program to create a new string where 'if' is added to the front of a given string. If the string already begins with 'if', return the string unchanged.

Sample Solution:

PHP Code :

<?php
// Define a function named "test" that takes a parameter $s
function test($s)
{
    // Check if the length of $s is greater than or equal to 2 AND if the substring of $s from index 0 to 1 is equal to "if"
    if (strlen($s) >= 2 && substr($s, 0, 2) == "if")
    {
        // If true, return $s as it is
        return $s;
    }

    // If false, prepend "if " to $s and return the result
    return "if " . $s;
}

// Call the test function with argument "if else" and echo the result
echo test("if else") . "\n";

// Call the test function with argument "else" and echo the result
echo test("else") . "\n";

// Call the test function with argument "if" and echo the result
echo test("if") . "\n";
?>

Explanation:

Function Definition:

The function test is defined with a single parameter $s.

Condition Check:

The function checks two conditions:

The length of $s is at least 2 characters (strlen($s) >= 2).
The first two characters of $s are "if" (substr($s, 0, 2) == "if").

If both conditions are true, it returns $s unchanged.

Return Value:

If either condition is false, the function prepends "if " to $s and returns the modified string.

Function Calls and Output:

First Call: echo test("if else")

The string starts with "if", so it returns "if else" unchanged.

Second Call: echo test("else")

The string does not start with "if", so it returns "if else".

Third Call: echo test("if")

The string starts with "if", so it returns "if" unchanged.

Output:

if else
if else
if

Flowchart:

For more Practice: Solve these Related Problems:

Write a PHP function to add "if" to the beginning of a string only if it does not already start with "if", using string comparison functions.
Write a PHP script to conditionally concatenate "if" to an input string and handle cases with different letter cases.
Write a PHP program to detect the presence of the substring "if" at the start of a string and prepend it only if absent, using regular expressions.
Write a PHP script to insert "if" at the beginning of a string by checking its first two characters without using strpos().

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