Javascript implementation of the Luhn algorithm to verify credit card numbers

verifyCreditCardNumber.js

        /**
         * [verifyCardNumber implements the Luhn algorithm (http://en.wikipedia.org/wiki/Luhn_algorithm), which is a checksum algorithm to determine card validity. This implementation was developed by BrainJar (http://www.brainjar.com/js/validation/default2.asp)]
         * @param  {[string]} _num [the credit card number in string format]
         * @return {Boolean}      [true if valid, else false]
         */
        function verifyCardNumber (_num) {
          var i, sum, digit, reverse, modified;
          // First, reverse the string and remove any non-numeric characters.
          reverse = '';

          for (i = 0; i < _num.length; i++) {
            digit = parseInt(_num.charAt(i), 10);
            if (digit >= 0 && digit <= 9) {
              reverse = digit + reverse;
            }
          }

          // Check for a bad string.
          if (reverse.length <= 1) {
            return false;
          }

          // Now run through each single digit to create a new string. Even digits are multiplied by two, odd digits are left alone.
          modified = '';

          for (i = 0; i < reverse.length; i++) {
            digit = parseInt(reverse.charAt(i), 10);

            if (i % 2 !== 0) {
              digit *= 2;
            }

            modified = modified + digit;
          }

          // Finally, add up all the single digits in this string.
          sum = 0;

          for (i = 0; i < modified.length; i++) {
            digit = parseInt(modified.charAt(i), 10);
            sum = sum + digit;
          }

          // If the resulting sum is an even multiple of ten (but not zero), the card number is good.
          if (sum !== 0 && sum % 10 === 0) {
            return true;
          } else {
            return false;
          }
        }

Hello am trying to create a c++ programme that allows you to enter the meter number and generates for you the token number 19 digits please help am stuck.Thanks