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PHP Exercises: Create a string like "aababcabcd" from a given string "abcd"

PHP Basic Algorithm: Exercise-30 with Solution

Write a PHP program to create a string like "aababcabcd" from a given string "abcd".

Sample Solution:

PHP Code :

<?php
function test($s)
{
  $result = "";
            for ($i = 0; $i < strlen($s); $i++)
            {
                $result = $result.substr($s, 0, $i + 1);
            }
            return $result;
 }

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

Sample Output:

aababcabcd
aababc
a

Flowchart:

Flowchart: Create a string like 'aababcabcd' from a given string 'abcd'.

PHP Code Editor:

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Previous: Write a PHP program to create a new string made of every other character starting with the first from a given string.
Next: Write a PHP program to count a substring of length 2 appears in a given string and also as the last 2 characters of the string. Do not count the end substring.

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.