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You will create a program that converts an integer to a Roman Numeral.

• Roman Numerals
• Array.splice()
• Array.indexOf()
• Array.join()

Creating two arrays, one with the Roman Numerals and one with the decimal equivalent for the new forms will be very helpful.

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If you add the numbers to the arrays that go before the new letter is introduced, like values for 4, 9, and 40, it will save you plenty of code.

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You can't have more than three consecutive Roman numerals together.

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Solution ahead!

var convertToRoman = function(num) {

  var decimalValue = [ 1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1 ];
  var romanNumeral = [ 'M', 'CM', 'D', 'CD', 'C', 'XC', 'L', 'XL', 'X', 'IX', 'V', 'IV', 'I' ];

  var romanized = '';

  for (var index = 0; index < decimalValue.length; index++) {
    while (decimalValue[index] <= num) {
      romanized += romanNumeral[index];
      num -= decimalValue[index];
    }
  }

  return romanized;
}

// test here
convertToRoman(36);

🚀 Run Code

• We start off by creating two arrays with default conversion with matching indices. These are called decimalValue and romanNumeral. We also create an empty string variable, romanized, which will house the final roman number.
• Using a for loop, we loop through the indicies of the decimalValue array. We continue to loop until while the value at the current index will fit into num.
• Next, we add the roman numeral and decrease num by the decimal equivalent.
• Finally, we return the value of romanized.

• For Loops
• While Loops

function convertToRoman(num) {
 var romans = ["I", "V", "X", "L", "C", "D", "M"],
     ints = [],
     romanNumber = [],
     numeral = "";
  while (num) {
    ints.push(num % 10);
    num = Math.floor(num/10);
  }
  for (i=0; i<ints.length; i++){
      units(ints[i]);
  }
  function units(){
    numeral = romans[i*2];
    switch(ints[i]) {
      case 1:
        romanNumber.push(numeral);
        break;
      case 2:
        romanNumber.push(numeral.concat(numeral));
        break;
      case 3:
        romanNumber.push(numeral.concat(numeral).concat(numeral));
        break;
      case 4:
        romanNumber.push(numeral.concat(romans[(i*2)+1]));
        break;
      case 5:
        romanNumber.push(romans[(i*2)+1]);
        break;
      case 6:
        romanNumber.push(romans[(i*2)+1].concat(numeral));
        break;
      case 7:
        romanNumber.push(romans[(i*2)+1].concat(numeral).concat(numeral));
        break;
      case 8:
        romanNumber.push(romans[(i*2)+1].concat(numeral).concat(numeral).concat(numeral));
        break;
      case 9:
        romanNumber.push(romans[i*2].concat(romans[(i*2)+2]));
      }
    }
  return romanNumber.reverse().join("").toString();
}

// test here
convertToRoman(97);

🚀 Run Code

• Create an array of Roman Numerals (romans).
• Use a for loop to create an array of the digits (ints) in the number.
• Loop through the array of digits (base 10) and as you do, increment the Roman Numeral (base 5) index by 2 (numeral = romans[i*2]).
• Within the loop, use Switch Case to push the proper Roman Numerals (backwards) onto that array.
• Reverse the Roman Numerals array and turn it into a string.

• For Loops
• While Loops
• Math

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Thanks @Rafase282 @SaintPeter @benschac @mrthnmn for your help with Algorithm: Roman Numeral Converter

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