Hi Guys,
Sometimes we need to replace some occurrences of string like, replace 2,3 occurrences of given string, then it creates a problem for us to manage that and to replace that particular occurrences.
To solve this problem I have made a function named "str_rep", which replaces the string occurrences at our given position. Here is that function
str_rep($search,$replace,$occurance,$string)

1.	$search-> The string which will going to replace
2.	$replace-> new string which will replace the search string. This parameter takes two types of values
a.	Array, for example $rep=array("ravi","sunil");
b.	String: this can be written in two manners
i.	Comma Separated: $rep="ravi,sunil";
ii.	Simple Value: $rep="ravi";
3.	$occurance-> at what occurance we want to replace that certain string. This parameter takes three types of values
a.	Array, for example $occ=array("1","2");
b.	Integer, for example $occ1=2;
c.	String: this can be written in two manners
i.	Comma Separated: $occ2="1,2";
ii.	Simple Value: $occ3="1";
4.	$string-> The string that is going to manipulate.

NOTE: if length of replace array and occurrence array wont be same then it will replace the last found string with that occurrences. Means length(occurance)>length($replace).

The Code for this function is as follows:

//Author Ravi Kumar (+91-9351264743)
class str_rep
{
	function str_rep($search,$replace,$occurance,$string)
	{			
		$finalstr="";
		$list=explode($search,$string);
		if(is_string($replace))
			$replace=explode(",",$replace);	
		if(is_string($occurance))
			$occurance=explode(",",$occurance);
		if(is_array($occurance)||is_string($occurance))
		{
			$i=0;	
			$replace_new="";		
			while($i<count($occurance))
			{
				if(isset($replace[$i]))
					$replace_new=$replace[$i];
				$list[$occurance[$i]-1].=$replace_new;
				$i++;
			}
			$i=0;
			while($i<count($list))
			{
				if($i==$occurance[$i]-1)
					$finalstr.=$list[$i];
				else
					$finalstr.=$list[$i].$search;
				$i++;
			}
		}
		else
		{
			$list[$occurance-1].=$replace;
			$i=0;
			while($i<count($list))
			{
				if($i==$occurance-1)
					$finalstr.=$list[$i];
				else
					$finalstr.=$list[$i].$search;
				$i++;
			}
		}			
		return $finalstr;
	}
}

example
$strrep=new str_rep;
$occ=array("1","2");
$occ1=array("ravi","sunil123");
echo $strrep->str_rep("<br />",$occ1,$occ,$desc);