1. PHP Function

2. String Function Function strcmp()
Compare two strings (case-sensitive):
strcasecmp()
Compare two strings (case-insensitive):
strlen()
returns the length of a string
substr()
function returns a part of a string
 substr_count()
counts the number of times a substring occurs in a string
strtok()
splits a string into smaller strings (tokens).
str_split()
The str_split() function splits a string into an array.

3. Function
example
output
strcmp()
echo strcmp("Hello world!","Hello world!");
strcasecmp()
echo strcasecmp("Hello world!","HELLO WORLD!");
strlen()
echo strlen("Hello"); 5
substr()
echo substr("Hello world",6);
echo substr("Hello world",10)."<br>"; echo substr("Hello world",1)."<br>"
World
d ello world
 substr_count()
echo substr_count("Hello world. The world is nice","world"); 2

4. Function
Example
Output
strtok()
$string = "Hello world. Beautiful day today."; $token = strtok($string, " "); while ($token !== false) { echo "$token<br>"; $token = strtok(" "); } 
Hello world. Beautiful day today.
str_split()
print_r(str_split("Hello"));
Array ( [0] => H [1] => e [2] => l [3] => l [4] => o )

5. Array Function Function sort() sort arrays in ascending order rsort()
- sort arrays in descending order
count()
returns the number of elements in an array.
array_key_exists()
function checks an array for a specified key, and returns true if the key exists and false if the
key does not exist.
 array_keys()
function returns an array containing the keys

6. Function
example
Output
sort()
$cars = array("Volvo", "BMW", "Toyota"); sort($cars); $clength = count($cars); for($x = 0; $x <  $clength; $x++) {      echo $cars[$x];      echo "<br>";}
BMW Toyota Volvo
rsort()
$cars = array("Volvo", "BMW", "Toyota"); rsort($cars); $clength = count($cars); for($x = 0; $x <  $clength; $x++) {      echo $cars[$x];      echo "<br>";}
Volvo Toyota BMW
count()
$cars=array("Volvo","BMW","Toyota"); echo count($cars); 3

7. Function
example
Output
array_key_exists()
$a=array("Volvo"=>"XC90","BMW"=>"X5"); if (array_key_exists("Volvo",$a))    {    echo "Key exists!";    } else    {    echo "Key does not exist!";    }
Key exists
 array_keys()
$a=array("Volvo"=>"XC90","BMW"=>"X5","Toyota"=>"Highlander"); print_r(array_keys($a));
Array ( [0] => Volvo [1] => BMW [2] => Toyota )