strtr() function replaces specified character of a string to another character.

<?PHP
	$str="The best time is no time at that time";
	$str2=strtr($str,'t','d');
	echo $str2; //The besd dime is no dime ad dhad dime
	$str3=strtr($str,'ta','di');
	echo $str3; //The besd dime is no dime id dhid dime
?>

The function can also only have 2 parameters, the 1st is the target string, the 2nd is an associated array, and the key or the associated array will be replaced with its relative value.

<?PHP
	$str="The best time is no time at that time";
	$arr=array("is"=>"was", "no"=>"the first");
	$str2=strtr($str,$arr);
	echo $str2; //The best time was the first time at that time
?>