1:

 $string  = 'Encoding and Decoding Encrypted PHP Code';
$encoded = base64_encode($string);
$decoded = base64_decode($encoded);
echo $encoded ."\n";
echo $decoded;

2:
if (function_exists('imap_open')) {
    echo "IMAP functions are available.<br />\n";
} else {
    echo "IMAP functions are not available.<br />\n";
}

3:

similar_text("Hello World","Hello World",$percent);
echo $percent;
 4:

 $str="shyam karan sahani";
 echo str_ireplace('sahani','Yadav',$str);
echo str_ireplace("WORLD","Peter","Hello good world!");
   
5: This function use for repeat text enter no. time

echo str_repeat("Love You",10); 

6: 
<?php
echo strcasecmp("Hello world!","HELLO shyam!");
?>

<p>If this function returns 0, the two strings are equal. other this is return cmp value</p>
it's not cse senstive
7:
   echo strcmp("Hello world!","Hello world!");

<p>If this function returns 0, the two strings are equal.Case senstive campare. this function you can use in password compaire </p>
8:

$str = "An example of a long word is: Supercalifragulistic";
echo wordwrap($str,15,"<br>\n");

Definition and Usage :

The wordwrap() function wraps a string into new lines when it reaches a specific length.

this function you can use for show excerpt;

Note: This function may leave white spaces at the beginning of a line.