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PHP Exercises: Exchange the first and last characters in a given string and return the new string

PHP Basic Algorithm: Exercise-7 with Solution

Write a PHP program to exchange the first and last characters in a given string and return the new string.

Sample Solution:

PHP Code :

<?php
function test($str) 
{
   return strlen($str) > 1 ? substr($str, strlen($str) - 1).substr($str, 1, strlen($str) - 2). substr($str, 0, 1) : $str;
   
}

echo test("abcd")."\n";
echo test("a")."\n";
echo test("xy")."\n";

Sample Output:

dbca
a
yx

Pictorial Presentation:

PHP Basic Algorithm Exercises: Remove the character in a given position of a given string.

Flowchart:

Flowchart: Remove the character in a given position of a given string.

PHP Code Editor:

Contribute your code and comments through Disqus.

Previous: Write a PHP program to remove the character in a given position of a given string. The given position will be in the range 0..string length -1 inclusive.
Next: Write a PHP program to create a new string which is 4 copies of the 2 front characters of a given string. If the given string length is less than 2 return the original string.

What is the difficulty level of this exercise?



PHP: Tips of the Day

$GLOBALS: An associative array containing references to all variables which are currently defined in the global scope of the script. The variable names are the keys of the array

Example:

<?php
$myGlobal = "global"; // declare variable outside of scope
function test()
{
$myLocal = "local"; // declare variable inside of scope
 // both variables are printed
 var_dump($myLocal);
 var_dump($GLOBALS["myGlobal"]);
}
test(); // run function
// only $myGlobal is printed since $myLocal is not globally scoped
 
var_dump($myLocal);
var_dump($myGlobal); 
?>

Output:

string(5) "local"
string(6) "global"
NULL
string(6) "global"

In the above example $myLocal is not displayed the second time because it is declared inside the test() function and then destroyed after the function is closed.

Becoming global

To remedy this there are two options.

Option one: global keyword

function test()
{
 global $myLocal;
 $myLocal = "local";
 var_dump($myLocal);
 var_dump($GLOBALS["myGlobal"]);
}

The global keyword is a prefix on a variable that forces it to be part of the global scope.

Note that you cannot assign a value to a variable in the same statement as the global keyword. Hence, why I had to assign a value underneath. (It is possible if you remove new lines and spaces but I don't think it is neat. global $myLocal; $myLocal = "local").

Option two: $GLOBALS array

function test()
{
 $GLOBALS["myLocal"] = "local";
 $myLocal = $GLOBALS["myLocal"];
 var_dump($myLocal);
 var_dump($GLOBALS["myGlobal"]);
}

In this example I reassigned $myLocal the value of $GLOBAL["myLocal"] since I find it easier writing a variable name rather than the associative array.