将罗马数字转换为1到3999之间十进制数的PHP程序

<?php
function romanValue($ch){
   // intializing the value to store decimal value of roman symbol
   $val = -1;
   if ($ch == 'I')
      $val = 1;
   else if ($ch == 'V')
      $val = 5;
   else if ($ch == 'X')
      $val = 10;
   else if ($ch == 'L')
      $val = 50;
   else if ($ch == 'C')
     $val = 100;
   else if ($ch == 'D')
     $val = 500;
   else if ($ch == 'M')
     $val = 1000; 
   return $val;
} 
// created a function to return decimal value of given roman value
function convertRomanToDecimal(&$str){
   // create variable decValue that we have to return and assign 0 to it 
   $decValue = 0;
   $n = strlen($str); // Getting the size of the given string 
   // calculate decValue while traversing the given string using for loop
   for ($i = 0; $i < $n; $i++) {
      // Store decimal value of romanValue str[i]
      $current = romanValue($str[$i]); 
      // check i+1 char exist
      if ($i+1 < $n) {
         // Store the decimal value of romanValue str[i+1]
         $next = romanValue($str[$i + 1]); 
         // check which value is greater current or next
         if ($current >= $next) {
            // if current value >= next value add value to the decValue
            $decValue = $decValue + $current;
         } else {
            // if current value < next value then add difference of value of next to current to the decValue
            $decValue = $decValue + $next - $current; 
            // Increment the index of the string to point to the next char
            $i++; 
         }
      }
      // If i+1 char not exist
      else {
         // Add current value to the decValue variable
         $decValue = $decValue + $current; 
         // Increment the index of the string to point to the next char
         $i++; 
      }
   }
   // Return decimal value
   return $decValue;
} 
$str ="DCCCLXXIV"; // Given Roman numeral string
// Print the decimal form and call the function of conversion
echo "The decimal Numeral form of the Roman Numeral is " . convertRomanToDecimal($str) . "";
?>