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PHP Exercises: Count the string "aa" in a given string and assume "aaa" contains two "aa"

PHP Basic Algorithm: Exercise-27 with Solution

Write a PHP program to count the string "aa" in a given string and assume "aaa" contains two "aa".

Sample Solution:

PHP Code :

<?php
function test($s)
{
   $ctr_aa = 0;
   for ($i = 0; $i < (strlen($s) - 1); $i++)
            {
                if (substr($s, $i, 2) == "aa")
                {
                    $ctr_aa++;
                }
            }
            return $ctr_aa;
 }


echo test("bbaaccaag")."\n";
echo test("jjkiaaasew")."\n";
echo test("JSaaakoiaa")."\n";

Sample Output:

2
2
3

Pictorial Presentation:

PHP Basic Algorithm Exercises: Count the string 'aa' in a given string and assume 'aaa' contains two 'aa'.

Flowchart:

Flowchart: Count the string 'aa' in a given string and assume 'aaa' contains two 'aa'.

PHP Code Editor:

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Previous: Write a PHP program to create a new string which is n (non-negative integer) copies of the the first 3 characters of a given string. If the length of the given string is less than 3 then return n copies of the string.
Next: Write a PHP program to check if the first appearance of "a" in a given string is immediately followed by another "a".

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.