Convert number to word in php

 <?php  
           function convert_number_to_words($number) {  
           $hyphen   = '-';  
           $conjunction = ' and ';  
           $separator  = ', ';  
           $negative  = 'negative ';  
           $decimal   = ' point ';  
           $dictionary = array(  
           0          => 'zero',  
           1          => 'one',  
           2          => 'two',  
           3          => 'three',  
           4          => 'four',  
           5          => 'five',  
           6          => 'six',  
           7          => 'seven',  
           8          => 'eight',  
           9          => 'nine',  
           10         => 'ten',  
           11         => 'eleven',  
           12         => 'twelve',  
           13         => 'thirteen',  
           14         => 'fourteen',  
           15         => 'fifteen',  
           16         => 'sixteen',  
           17         => 'seventeen',  
           18         => 'eighteen',  
           19         => 'nineteen',  
           20         => 'twenty',  
           30         => 'thirty',  
           40         => 'fourty',  
           50         => 'fifty',  
           60         => 'sixty',  
           70         => 'seventy',  
           80         => 'eighty',  
           90         => 'ninety',  
           100         => 'hundred',  
           1000        => 'thousand',  
           1000000       => 'million',  
           1000000000     => 'billion',  
           1000000000000    => 'trillion',  
           1000000000000000  => 'quadrillion',  
           1000000000000000000 => 'quintillion'  
           );  
           if (!is_numeric($number)) {  
           return false;  
           }  
           if (($number >= 0 && (int) $number < 0) || (int) $number < 0 - PHP_INT_MAX) {  
           // overflow  
           trigger_error(  
           'convert_number_to_words only accepts numbers between -' . PHP_INT_MAX . ' and ' . PHP_INT_MAX,  
           E_USER_WARNING  
           );  
           return false;  
           }  
           if ($number < 0) {  
           return $negative . convert_number_to_words(abs($number));  
           }  
           $string = $fraction = null;  
           if (strpos($number, '.') !== false) {  
           list($number, $fraction) = explode('.', $number);  
           }  
           switch (true) {  
           case $number < 21:  
           $string = $dictionary[$number];  
           break;  
           case $number < 100:  
           $tens  = ((int) ($number / 10)) * 10;  
           $units = $number % 10;  
           $string = $dictionary[$tens];  
           if ($units) {  
           $string .= $hyphen . $dictionary[$units];  
           }  
           break;  
           case $number < 1000:  
           $hundreds = $number / 100;  
           $remainder = $number % 100;  
           $string = $dictionary[$hundreds] . ' ' . $dictionary[100];  
           if ($remainder) {  
           $string .= $conjunction . convert_number_to_words($remainder);  
           }  
           break;  
           default:  
           $baseUnit = pow(1000, floor(log($number, 1000)));  
           $numBaseUnits = (int) ($number / $baseUnit);  
           $remainder = $number % $baseUnit;  
           $string = convert_number_to_words($numBaseUnits) . ' ' . $dictionary[$baseUnit];  
           if ($remainder) {  
           $string .= $remainder < 100 ? $conjunction : $separator;  
           $string .= convert_number_to_words($remainder);  
           }  
           break;  
           }  
           if (null !== $fraction && is_numeric($fraction)) {  
           $string .= $decimal;  
           $words = array();  
           foreach (str_split((string) $fraction) as $number) {  
           $words[] = $dictionary[$number];  
           }  
           $string .= implode(' ', $words);  
           }  
           return $string;  
           }  
           ?>  

 Input :   
 echo convert_number_to_words(2500);  
 Output:  
 TWO THOUSAND, FIVE HUNDRED